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[[Image:Cyclone Catarina from the ISS on March 26 2004.JPG|thumb|250px|[[Cyclone Catarina]], a rare [[South Atlantic tropical cyclone]] viewed from the [[International Space Station]] on [[March 26]] [[2004]]]]
{{tropical cyclone}}{{Redirect|Hurricane}}

A '''tropical cyclone''' is a [[storm|storm system]] characterized by a [[low pressure system|low pressure]] center and numerous [[thunderstorms]] that produce strong winds and [[flood]]ing [[rain]]. Tropical cyclones feed on heat released when moist [[air]] rises, resulting in [[condensation]] of [[water vapour]] contained in the moist air. They are fueled by a different heat mechanism than other cyclonic windstorms such as [[nor'easter]]s, [[European windstorm]]s, and [[polar low]]s, leading to their classification as "warm core" storm systems.

The term "tropical" refers to both the geographic origin of these systems, which form almost exclusively in [[tropics|tropical]] regions of the globe, and their formation in [[Air mass#Classification|Maritime Tropical air masses]]. The term "cyclone" refers to such storms' [[cyclone|cyclonic]] nature, with [[Clockwise and counterclockwise|counterclockwise]] rotation in the [[Northern Hemisphere]] and clockwise rotation in the [[Southern Hemisphere]]. Depending on their location and strength, tropical cyclones are referred to by other names, such as '''hurricane''', '''typhoon''', '''tropical storm''', '''cyclonic storm''', '''tropical depression''' and simply '''cyclone'''.

While tropical cyclones can produce extremely powerful winds and torrential [[rain]], they are also able to produce high waves and damaging [[storm surge]]. They develop over large bodies of warm water, and lose their strength if they move over land. This is the reason coastal regions can receive significant damage from a tropical cyclone, while inland regions are relatively safe from receiving strong winds. Heavy rains, however, can produce significant flooding inland, and storm surges can produce extensive coastal [[flood]]ing up to {{convert|40|km|mi}} from the coastline. Although their effects on human populations can be devastating, tropical cyclones can also relieve [[drought]] conditions. They also carry heat and energy away from the tropics and transport it toward [[temperate]] [[latitudes]], which makes them an important part of the global [[atmospheric circulation]] mechanism. As a result, tropical cyclones help to maintain equilibrium in the Earth's [[troposphere]], and to maintain a relatively stable and warm temperature worldwide.

Many tropical cyclones [[tropical cyclogenesis|develop]] when the atmospheric conditions around a weak disturbance in the atmosphere are favorable. Others form when [[#Related cyclone types|other types of cyclones]] acquire tropical characteristics. Tropical systems are then moved by [[#Steering winds|steering winds]] in the [[troposphere]]; if the conditions remain favorable, the tropical disturbance intensifies, and can even develop an [[eye (cyclone)|eye]]. On the other end of the spectrum, if the conditions around the system deteriorate or the tropical cyclone makes landfall, the system weakens and eventually dissipates. In spite of this, it is not possible to artificially induce the dissipation of these systems with current technology.

==Physical structure==
{{Seealso|Eye (cyclone)}}
[[Image:Hurricane structure graphic.jpg|thumb|250px|right|Structure of a tropical cyclone]]
All tropical cyclones are areas of [[low pressure area|low]] [[atmospheric pressure]] near the Earth's surface. The pressures recorded at the centers of tropical cyclones are among the lowest that occur on Earth's surface at [[sea level]].<ref name="ABC pressures">{{cite news | author = Symonds, Steve |title = Highs and Lows | work = Wild Weather | publisher = [[Australian Broadcasting Corporation]] | date = [[November 17]], [[2003]] | accessdate = 2007-03-23 | url = http://www.abc.net.au/northcoast/stories/s989385.htm}}</ref> Tropical cyclones are characterized and driven by the release of large amounts of latent [[heat of condensation]], which occurs when moist air is carried upwards and its water vapor condenses. This heat is distributed vertically around the center of the storm. Thus, at any given altitude (except close to the surface, where water temperature dictates air temperature) the environment inside the cyclone is warmer than its outer surroundings.<ref name = "AOML FAQ A7">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: What is an extra-tropical cyclone? | publisher = [[NOAA]] | accessdate = 2007-03-23 | url = http://www.aoml.noaa.gov/hrd/tcfaq/A7.html}}</ref>



===Eye and inner core===
A strong tropical cyclone will harbor an area of sinking air at the center of circulation. If this area is strong enough, it can develop into an [[eye (cyclone)|eye]]. Weather in the eye is normally calm and free of clouds, although the sea may be extremely violent.<ref name="JetStream structure">{{cite web | url = http://www.srh.noaa.gov/jetstream/tropics/tc_structure.htm | author = [[National Weather Service]] | publisher = [[National Oceanic & Atmospheric Administration]] | title = Tropical Cyclone Structure | accessdate = 2006-12-14 | work = JetStream - An Online School for Weather | date = [[October 19]], [[2005]]}}</ref> The eye is normally circular in shape, and may range in size from {{convert|3|km|mi}} to {{convert|370|km|mi}} in diameter.<ref name="WilmaTCR">{{cite web|last=Pasch|first=Richard J.|coauthors=Eric S. Blake, Hugh D. Cobb III, and David P. Roberts | url=http://www.nhc.noaa.gov/pdf/TCR-AL252005_Wilma.pdf | format=PDF | title= Tropical Cyclone Report: Hurricane Wilma: 15-25 October 2005 | publisher=[[National Hurricane Center]] | date=[[September 28]], [[2006]]|accessdate=2006-12-14}}</ref><ref name="MWR Lander 1999">{{cite journal | author = Lander, Mark A. | title = A Tropical Cyclone with a Very Large Eye | url = http://ams.allenpress.com/archive/1520-0493/127/1/pdf/i1520-0493-127-1-137.pdf | format =PDF | journal = [[Monthly Weather Review]] | date = January 1999 | volume = 127 | issue = 1 | accessdate=2006-12-14}}</ref> Intense, mature tropical cyclones can sometimes exhibit an inward curving of the eyewall's top, making it resemble a football stadium; this phenomenon is thus sometimes referred to as the ''[[Eye (cyclone)#Stadium effect|stadium effect]]''.<ref name="MWR 1996 AHS summary">{{cite journal | author = Pasch, Richard J. and [[Lixion Avila|Lixion A. Avila]] | title = Atlantic Hurricane Season of 1996 | journal = [[Monthly Weather Review]] | pages = 581–610 | url = http://ams.allenpress.com/archive/1520-0493/127/5/pdf/i1520-0493-127-5-581.pdf | format = PDF | date = May 1999 | volume = 127 | issue = 5 | accessdate = 2006-12-14 | doi = 10.1175/1520-0493(1999)127<0581:AHSO>2.0.CO;2 | doilabel = 10.1175/1520-0493(1999)127&#60;0581:AHSO&#62;2.0.CO;2}}</ref>

There are other features that either surround the eye, or cover it. The [[central dense overcast]] is the concentrated area of strong thunderstorm activity near the center of a tropical cyclone;<ref name="CDO AMS">{{cite web|author = [[American Meteorological Society]] | url = http://amsglossary.allenpress.com/glossary/browse?s=c&p=19 | title = AMS Glossary: C | work = Glossary of Meteorology | accessdate=2006-12-14 | publisher = [[Allen Press]]}}</ref> in weaker tropical cyclones, the CDO may cover the center completely.<ref name = "AOML FAQ A9">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: What is a "CDO"? | publisher = [[NOAA]] | accessdate = 2007-03-23 | url = http://www.aoml.noaa.gov/hrd/tcfaq/A9.html}}</ref> The [[eyewall]] is a circle of strong thunderstorms that surrounds the eye; here is where the greatest wind speeds are found, where clouds reach the highest, and precipitation is the heaviest. The heaviest wind damage occurs where a tropical cyclone's eyewall passes over land.<ref name="JetStream structure"/> [[Eye (cyclone)#Eyewall replacement cycles|Eyewall replacement cycles]] occur naturally in intense tropical cyclones. When cyclones reach peak intensity they usually have an eyewall and [[radius of maximum wind]]s that contract to a very small size, around {{convert|10|km|mi}} to {{convert|25|km|mi}}. Outer rainbands can organize into an outer ring of thunderstorms that slowly moves inward and robs the inner eyewall of its needed moisture and [[angular momentum]]. When the inner eyewall weakens, the tropical cyclone weakens (in other words, the maximum sustained winds weaken and the central pressure rises.) The outer eyewall replaces the inner one completely at the end of the cycle. The storm can be of the same intensity as it was previously or even stronger after the eyewall replacement cycle finishes. The storm may strengthen again as it builds a new outer ring for the next eyewall replacement.<ref name = "AOML FAQ D8">{{cite web | author = Atlantic Oceanographic and Hurricane Research Division | title = Frequently Asked Questions: What are "concentric eyewall cycles" (or "eyewall replacement cycles") and why do they cause a hurricane's maximum winds to weaken? | publisher = [[NOAA]] | accessdate = 2006-12-14 | url = http://www.aoml.noaa.gov/hrd/tcfaq/D8.html}}</ref>

{|class="wikitable" style="float: right; font-size: 92%; margin-right: 0px;"
! colspan=2 style="background: #ccf;" | Size descriptions of tropical cyclones
|-
! ROCI || Type
|-
| Less than 2&nbsp;degrees latitude || Very small/midget
|-
| 2 to 3&nbsp;degrees of latitude || Small
|-
| 3 to 6&nbsp;degrees of latitude || Medium/Average
|-
| 6 to 8&nbsp;degrees of latitude || Large
|-
| Over 8&nbsp;degrees of latitude || Very large<ref name="JTWCsize">Joint Typhoon Warning Center. [https://metocph.nmci.navy.mil/jtwc/menu/JTFAQ.html#tcsize Q: What is the average size of a tropical cyclone?] Retrieved on [[2007-07-04]].</ref>
|-
|}

===Size===
One measure of the size of a tropical cyclone is determined by measuring the distance from its center of circulation to its outermost closed [[Contour line|isobar]], also known as its [[Radius of outermost closed isobar|ROCI]]. If the radius is less than two [[latitude|degrees of latitude]] or {{convert|222|km|mi}}, then the cyclone is "very small" or a "midget".A Radius between 3 and 6&nbsp;latitude degrees or {{convert|333|km|mi}} to {{convert|666|km|mi}} are considered "average sized". "Very large" tropical cyclones have a radius of greater than 8&nbsp;degrees or {{convert|888|km|mi}}.<ref name="JTWCsize">Joint Typhoon Warning Center. [https://metocph.nmci.navy.mil/jtwc/menu/JTFAQ.html#tcsize Q: What is the average size of a tropical cyclone?] Retrieved on [[2007-07-04]].</ref> Use of this measure has objectively determined that tropical cyclones in the northwest Pacific ocean are the largest on earth on average, with [[Atlantic tropical cyclone]]s roughly half their size.<ref name="Merrill">Robert T. Merrill. [http://ams.allenpress.com/archive/1520-0493/112/7/pdf/i1520-0493-112-7-1408.pdf A Comparison of Large and Small Tropical Cyclones.] Retrieved on [[2008-07-14]].</ref> Other methods of determining a tropical cyclone's size include measuring the radius of gale force winds and measuring the radius at which its relative [[vorticity]] field decreases to 1×10<sup>-5</sup> s<sup>-1</sup> from its center.<ref>[[Bureau of Meteorology]]. [http://www.bom.gov.au/bmrc/pubs/tcguide/ch2/ch2_4.htm Australian Government Bureau of Meteorology] Retrieved on [[2008-02-24]].</ref><ref name="Liu / Chan AMS">{{cite journal|author=K. S. Liu and Johnny C. L. Chan | url =http://ams.allenpress.com/perlserv/?SESSID=28a79df53585df59461ab347756adff8&request=get-document&doi=10.1175%2F1520-0493(1999)127%3C2992%3ASOTCAI%3E2.0.CO%3B2 | title = Size of Tropical Cyclones as Inferred from ''ERS-1'' and ''ERS-2'' Data | accessdate = 2008-02-24 | month = December | year = 1999 | issue = 12 | volume = 127 | journal = [[Monthly Weather Review]] | pages = 2992 | doi = 10.1175/1520-0493(1999)127<2992:SOTCAI>2.0.CO;2 | doilabel = 10.1175/1520-0493(1999)127&#60;2992:SOTCAI&#62;2.0.CO;2}}</ref>

==Mechanics==
[[Image:Hurricane profile.svg|thumb|250px|right|Tropical cyclones form when the energy released by the condensation of moisture in rising air causes a [[positive feedback loop]] over warm ocean waters.<ref>[[Kerry Emanuel]]. [http://wind.mit.edu/~emanuel/anthro2.htm Anthropogenic Effects on Tropical Cyclone Activity.] Retrieved on [[2008-02-25]].</ref>]]

A tropical cyclone's primary energy source is the release of the [[heat of condensation]] from water vapor [[condensation|condensing]] at high altitudes, with [[solar heating]] being the initial source for evaporation. Therefore, a tropical cyclone can be visualized as a giant vertical [[heat engine]] supported by mechanics driven by physical forces such as the [[rotation]] and [[gravity]] of the Earth.<ref name = "NOAA preparedness">{{cite web | author = [[National Weather Service]] | date = September 2006 | title = Hurricanes... Unleashing Nature's Fury: A Preparedness Guide | publisher = [[NOAA]] | accessdate = 2006-12-02 | format = PDF | url = http://www.srh.noaa.gov/fwd/wcm/hurric.pdf}}</ref> In another way, tropical cyclones could be viewed as a special type of [[Mesoscale Convective Complex|mesoscale convective complex]], which continues to develop over a vast source of relative warmth and moisture. Condensation leads to higher wind speeds, as a tiny fraction of the released energy is converted into mechanical energy;<ref name = "AOML FAQ C5c">{{ cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: Why don't we try to destroy tropical cyclones by nuking them? | publisher = [[NOAA]] | accessdate = 2006-07-25|url = http://www.aoml.noaa.gov/hrd/tcfaq/C5c.html}}</ref> the faster winds and lower pressure associated with them in turn cause increased surface evaporation and thus even more condensation. Much of the released energy drives [[vertical draft|updrafts]] that increase the height of the storm clouds, speeding up condensation.<ref name="NOAA Question of the Month">{{cite web | author = [[National Oceanic & Atmospheric Administration]] | url = http://www.noaa.gov/questions/question_082900.html | title = NOAA Question of the Month: How much energy does a hurricane release? | date = August 2001 | accessdate=2006-03-31 | publisher = [[NOAA]]}}</ref> This [[positive feedback loop]] continues for as long as conditions are favorable for [[tropical cyclogenesis|tropical cyclone development]]. Factors such as a continued lack of equilibrium in air mass distribution would also give supporting energy to the cyclone. The rotation of the Earth causes the system to spin, an effect known as the [[Coriolis effect]],<ref>[[Encyclopædia Britannica]]. [http://www.britannica.com/eb/topic-137646/article-9026305 Coriolis force (physics).] Retrieved on [[2008-02-25]].</ref> giving it a cyclonic characteristic and affecting the trajectory of the storm.<ref name="BritTCtrackcoriolis">[[Encyclopædia Britannica]]. [http://www.britannica.com/eb/article-247936/tropical-cyclone#849004.hook Tropical cyclone: Tropical cyclone tracks.] Retrieved on [[2008-02-25]].</ref>

What primarily distinguishes tropical cyclones from other meteorological phenomena is deep [[convection#Atmospheric heat-driven convection|convection]] as a driving force.<ref name="BOM Question 6">{{cite web | author = [[Bureau of Meteorology]] | work = Frequently Asked Questions | title = How are tropical cyclones different to mid-latitude cyclones? | url = http://www.bom.gov.au/weather/wa/cyclone/about/faq/faq_def_6.shtml | accessdate = 2006-03-31}}</ref> Because convection is strongest in a [[tropical climate]], it defines the initial domain of the tropical cyclone. By contrast, [[mid-latitude cyclone]]s draw their energy mostly from pre-existing horizontal temperature [[gradient]]s in the atmosphere.<ref name="BOM Question 6"/> To continue to drive its heat engine, a tropical cyclone must remain over warm water, which provides the needed atmospheric moisture to maintain the positive feedback loop running. When a tropical cyclone passes over land, it is cut off from its heat source and its strength diminishes rapidly.<ref name = "AOML FAQ C2">{{ cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: Doesn't the friction over land kill tropical cyclones?|publisher = [[NOAA]] | accessdate = 2006-07-25 | url = http://www.aoml.noaa.gov/hrd/tcfaq/C2.html}}</ref>

[[Image:GulfMexTemps 2005Hurricanes.gif|thumb|250px|Chart displaying the drop in surface temperature in the [[Gulf of Mexico]] as Hurricanes [[Hurricane Katrina|Katrina]] and [[Hurricane Rita|Rita]] passed over]]
The passage of a tropical cyclone over the ocean can cause the upper layers of the ocean to cool substantially, which can influence subsequent cyclone development. Cooling is primarily caused by upwelling of cold water from deeper in the ocean due to the wind. The cooler water causes the storm to weaken. This is a negative feedback process that causes the storms to weaken over sea because of their own effects. Additional cooling may come in the form of cold water from falling raindrops. Cloud cover may also play a role in cooling the ocean, by shielding the ocean surface from direct sunlight before and slightly after the storm passage. All these effects can combine to produce a dramatic drop in sea surface temperature over a large area in just a few days.<ref name="NASA Cooling">{{cite web | author = Eric A. D'Asaro and Peter G. Black. | url = http://opd.apl.washington.edu/~dasaro/DENNIS/HurrConf.pdf | title = J8.4 Turbulence in the Ocean Boundary Layer Below Hurricane Dennis | year = 2006 | accessdate = 2008-02-22 | publisher = [[University of Washington]]}}</ref>

Scientists at the US [[National Center for Atmospheric Research]] estimate that a tropical cyclone releases heat energy at the rate of 50 to 200&nbsp;[[exajoule]]s (10<sup>18</sup>&nbsp;J) per day,<ref name="NOAA Question of the Month"/> equivalent to about 1&nbsp;PW (10<sup>15</sup>&nbsp;watt). This rate of energy release is equivalent to 70 times the [[World energy resources and consumption|world energy consumption]] of humans and 200 times the world-wide electrical generating capacity,<ref name="NOAA Question of the Month"/> or to exploding a 10-[[megaton]] [[nuclear bomb]] every 20&nbsp;minutes.<ref name="UCAR">[[University Corporation for Atmospheric Research]]. [http://www.ucar.edu/news/features/hurricanes/index.jsp Hurricanes: Keeping an eye on weather's biggest bullies.] Retrieved on [[2006-03-31]].</ref>

While the most obvious motion of clouds is toward the center, tropical cyclones also develop an upper-level (high-altitude) outward flow of clouds. These originate from air that has released its moisture and is expelled at high altitude through the "chimney" of the storm engine.<ref name = "NOAA preparedness"/> This outflow produces high, thin [[cirrus cloud]]s that spiral away from the center. The clouds are thin enough for the sun to be visible through them. These high cirrus clouds may be the first signs of an approaching tropical cyclone.<ref name = "AOML FAQ H5">{{ cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: What's it like to go through a hurricane on the ground? What are the early warning signs of an approaching tropical cyclone?|publisher = [[NOAA]] | accessdate = 2006-07-26 | url = http://www.aoml.noaa.gov/hrd/tcfaq/H5.html}}</ref>

==Major basins and related warning centers==
{{main|Tropical cyclone basins|Regional Specialized Meteorological Centre|Tropical Cyclone Warning Centre}}
{| style="float: right; clear: right; background-color: transparent; margin-left: 0em"
|
{|class="wikitable" style="float: right; font-size: 92%; margin-right: 0px;"
! colspan=2 style="background: #ccf;" | Basins and [[World Meteorological Organization|WMO]] Monitoring Institutions<ref name = "AOML FAQ F1">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: What regions around the globe have tropical cyclones and who is responsible for forecasting there?|publisher = [[NOAA]] | accessdate = 2006-07-25 | url = http://www.aoml.noaa.gov/hrd/tcfaq/F1.html}}</ref>
|-
! Basin !! Responsible RSMCs and TCWCs
|-
| Northern Atlantic || [[National Hurricane Center]]
|-
| Northeastern Pacific || [[National Hurricane Center]]
|-
| North Central Pacific || [[Central Pacific Hurricane Center]]
|-
| Northwestern Pacific || [[Japan Meteorological Agency]]
|-
| Northern Indian Ocean || [[Indian Meteorological Department]]
|-
| Southwestern Indian Ocean || [[Météo-France]]
|-
| South and<br />Southwestern Pacific || [[Fiji Meteorological Service]]<br />[[Meteorological Service of New Zealand]]<sup>†</sup><br />Papua New Guinea National Weather Service<sup>†</sup><br />[[Bureau of Meteorology]]<sup>†</sup> (Australia)
|-
| Southeastern Indian Ocean|| [[Bureau of Meteorology]]<sup>†</sup> (Australia)<br />[[Badan Meteorologi dan Geofisika|Meteorological and Geophysical Agency]]<sup>†</sup> (Indonesia)
|-
! colspan=2 style="font-size: 92%; text-align: right;" | <sup>†</sup>: '''''Indicates a Tropical Cyclone Warning Centre'''''
|}
|-
|
[[Image:Global tropical cyclone tracks-edit2.jpg|thumb|right|250px|Map of the cumulative tracks of all tropical cyclones during the 1985–2005 time period. The [[Pacific Ocean]] west of the [[International Date Line]] sees more tropical cyclones than any other basin, while there is almost no activity in the [[Atlantic Ocean]] south of the [[Equator]].]]
|-
|}
[[Image:Tropical cyclones 1945 2006.png|thumb|right|250px|Map of all tropical cyclone tracks from 1945 to 2006. Equal-area projection.]]

There are six [[Regional Specialized Meteorological Centre]]s (RSMCs) worldwide. These organizations are designated by the [[World Meteorological Organization]] and are responsible for tracking and issuing bulletins, warnings, and advisories about tropical cyclones in their designated areas of responsibility. Additionally, there are six [[Tropical Cyclone Warning Centre]]s (TCWCs) that provide information to smaller regions.<ref name="WMO RSMC list">{{cite web | author = [[World Meteorological Organization]] | title = RSMCs | date = [[April 25]], [[2006]] | accessdate = 2006-11-05 | work = Tropical Cyclone Programme (TCP) | url = http://severe.worldweather.wmo.int/rsmcs.html}}</ref> The RSMCs and TCWCs are not the only organizations that provide information about tropical cyclones to the public. The [[Joint Typhoon Warning Center]] (JTWC) issues advisories in all basins except the Northern Atlantic for the purposes of the [[United States Government]].<ref>[[Joint Typhoon Warning Center]]. [https://metocph.nmci.navy.mil/jtwc/menu/JTWC_mission.html Joint Typhoon Warning Center Mission Statement.] Retrieved on [[2008-02-24]].</ref> The [[Philippine Atmospheric, Geophysical and Astronomical Services Administration]] (PAGASA) issues advisories and names for tropical cyclones that approach the [[Philippines]] in the Northwestern Pacific to protect the life and property of its citizens.<ref>[[Philippine Atmospheric, Geophysical and Astronomical Services Administration]]. [http://www.pagasa.dost.gov.ph/mission.shtml MISSION / VISION.] Retrieved on [[2008-02-24]].</ref> The [[Canadian Hurricane Centre]] (CHC) issues advisories on hurricanes and their remnants for Canadian citizens when they affect Canada.<ref>Canadian Hurricane Centre. [http://www.atl.ec.gc.ca/weather/hurricane/index_e.html Canadian Hurricane Centre.] Retrieved on [[2008-02-24]].</ref>

On [[March 26]], [[2004]], [[Cyclone Catarina]] became the first recorded [[South Atlantic tropical cyclone|South Atlantic cyclone]] and subsequently struck southern [[Brazil]] with winds equivalent to Category&nbsp;2 on the [[Saffir-Simpson Hurricane Scale]]. As the cyclone formed outside the authority of another warning center, Brazilian meteorologists initially treated the system as an [[extratropical cyclone]], although subsequently classified it as tropical.<ref name="Emerson Marcelino">{{cite web | author = Marcelino, Emerson Vieira; Isabela Pena Viana de Oliveira Marcelino; Frederico de Moraes Rudorff | title = Cyclone Catarina: Damage and Vulnerability Assessment | url = http://www.dsr.inpe.br/geu/Rel_projetos/Relatorio_IAI_Emerson_Marcelino.pdf | format = PDF | date = 2004 | accessdate = 2006-12-24 | publisher = Santa Catarina Federal University}}</ref>

==Formation==
{{main|Tropical cyclogenesis}}
===Times===
Worldwide, tropical cyclone activity peaks in late summer, when the difference between temperatures aloft and sea surface temperatures is the greatest. However, each particular basin has its own seasonal patterns. On a worldwide scale, May is the least active month, while September is the most active.<ref name = "AOML FAQ G1">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: When is hurricane season?|publisher = [[NOAA]] | accessdate = 2006-07-25 | url = http://www.aoml.noaa.gov/hrd/tcfaq/G1.html}}</ref>

In the Northern [[Atlantic Ocean]], a distinct hurricane season occurs from [[June 1]] to [[November 30]], sharply peaking from late August through September.<ref name = "AOML FAQ G1"/> The statistical peak of the [[Atlantic hurricane season]] is [[September 10]]. The Northeast [[Pacific Ocean]] has a broader period of activity, but in a similar time frame to the Atlantic.<ref name="NHC Atl climatology">{{cite web | author = McAdie, Colin | publisher = [[National Hurricane Center]] | title = Tropical Cyclone Climatology | url = http://www.nhc.noaa.gov/pastprofile.shtml | date = [[May 10]], [[2007]] | accessdate = 2007-06-09}}</ref> The Northwest Pacific sees tropical cyclones year-round, with a minimum in February and March and a peak in early September. In the North Indian basin, storms are most common from April to December, with peaks in May and November.<ref name = "AOML FAQ G1"/>

In the [[Southern Hemisphere]], tropical cyclone activity begins in late October and ends in May. Southern Hemisphere activity peaks in mid-February to early March.<ref name = "AOML FAQ G1"/>

<center>
{|class="wikitable" style="font-size: 92%;"
! colspan=6 style="background: #ccf;" | Season lengths and seasonal averages<ref name = "AOML FAQ G1"/><ref name = "AOML FAQ E10">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: What are the average, most, and least tropical cyclones occurring in each basin? | publisher = [[NOAA]] | accessdate = 2006-11-30 | url = http://www.aoml.noaa.gov/hrd/tcfaq/E10.html}}</ref>
|-
! Basin !! Season start !! Season end !! Tropical Storms<br />(>34&nbsp;[[knot (speed)|knot]]s) !! Tropical Cyclones<br />(>63&nbsp;knots)!! Category&nbsp;3+ [[Tropical cyclone|TC]]s<br />(>95&nbsp;knots)
|-
| Northwest Pacific || April || January || 26.7 || 16.9 || 8.5
|-
| South Indian || October || May || 20.6 || 10.3 || 4.3
|-
| Northeast Pacific || May || November || 16.3 || 9.0 || 4.1
|-
| North Atlantic || June || November || 10.6 || 5.9 || 2.0
|-
| Australia Southwest Pacific || October || May || 10.6 || 4.8 || 1.9
|-
| North Indian || April || December || 5.4 || 2.2 || 0.4
|}
</center>

===Factors===
[[Image:Atlantic hurricane graphic.gif|thumb|250px|right|Waves in the trade winds in the Atlantic Ocean—areas of converging winds that move along the same track as the prevailing wind—create instabilities in the atmosphere that may lead to the formation of hurricanes.]]

The formation of tropical cyclones is the topic of extensive ongoing research and is still not fully understood.<ref>Simon Ross. [http://books.google.com/books?id=JKTDenQB5nAC&pg=PT60&lpg=PT60&dq=formation+of+tropical+cyclones+not+fully+understood&source=web&ots=uEMxAWXIRj&sig=boncW6asDHVkKaT1I3i_df9bQ1Y Natural Hazards.] Retrieved on [[2008-02-24]].</ref> While six factors appear to be generally necessary, tropical cyclones may occasionally form without meeting all of the following conditions. In most situations, [[Sea surface temperature|water temperatures]] of at least {{convert|26.5|C|F}} are needed down to a depth of at least {{convert|50|m|ft}};<ref name = "AOML FAQ A15">{{ cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: How do tropical cyclones form? | publisher = [[NOAA]] | accessdate = 2006-07-26 | url = http://www.aoml.noaa.gov/hrd/tcfaq/A15.html}}</ref> waters of this temperature cause the overlying atmosphere to be unstable enough to sustain convection and thunderstorms.<ref name = "AOML FAQ A16">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: Why do tropical cyclones require {{convert|80|F|C}} ocean temperatures to form?|publisher = [[NOAA]] | accessdate = 2006-07-25 | url = http://www.aoml.noaa.gov/hrd/tcfaq/A16.html}}</ref> Another factor is rapid cooling with height, which allows the release of the [[heat of condensation]] that powers a tropical cyclone.<ref name = "AOML FAQ A15"/> High humidity is needed, especially in the lower-to-mid [[troposphere]]; when there is a great deal of moisture in the atmosphere, conditions are more favorable for disturbances to develop.<ref name = "AOML FAQ A15"/> Low amounts of [[wind shear]] are needed, as high shear is disruptive to the storm's circulation.<ref name = "AOML FAQ A15"/> Tropical cyclones generally need to form more than {{convert|555|km|mi}} or 5&nbsp;degrees of [[latitude]] away from the [[equator]], allowing the [[Coriolis effect]] to deflect winds blowing towards the low pressure center and creating a circulation.<ref name = "AOML FAQ A15"/> Lastly, a formative tropical cyclone needs a pre-existing system of disturbed weather, although without a circulation no cyclonic development will take place.<ref name = "AOML FAQ A15"/>

===Locations===
Most tropical cyclones form in a worldwide band of thunderstorm activity called by several names: the Intertropical Front (ITF),<ref>Marine Knowledge Centre. [http://www.knmi.nl/~koek/glossary.html#I Marine Meteorological Glossary: I.] Retrieved on [[2008-02-24]].</ref> the [[Intertropical Convergence Zone]] (ITCZ),<ref>[[Philippine Atmospheric, Geophysical and Astronomical Services Administration]]. [http://www.pagasa.dost.gov.ph/genmet/tropicalcyclone/formation_of_cyclone.html Formation of Tropical Cyclones.] Retrieved on [[2008-02-24]].</ref> or the [[monsoon trough]].<ref name="MILLER7">{{cite web | author = DeCaria, Alex | publisher = [[Millersville University of Pennsylvania|Millersville University]] | url = http://snowball.millersville.edu/~adecaria/ESCI344/esci344_lesson05_TC_climatology.html | title = Lesson 5 – Tropical Cyclones: Climatology. | work = ESCI 344 – Tropical Meteorology | year = 2005 | accessdate = 2008-02-22}}</ref> Another important source of atmospheric instability is found in [[tropical wave]]s, which cause about 85% of intense tropical cyclones in the Atlantic ocean,<ref name="MWR Avila 1995">{{cite journal | last = [[Lixion Avila|Avila, Lixion]] | coauthors = Richard Pasch | year = 1995 | month = March | title = Atlantic tropical systems of 1993 | journal = [[Monthly Weather Review]] | volume = 123 | issue = 3 | pages = 887&ndash;896 | url = http://ams.allenpress.com/perlserv/?request=res-loc&uri=urn%3Aap%3Apdf%3Adoi%3A10.1175%2F1520-0493%281995%29123%3C0887%3AATSO%3E2.0.CO%3B2 | format = PDF | accessdate = 2006-07-25 | doi = 10.1175/1520-0493(1995)123<0887:ATSO>2.0.CO;2 | doilabel = 10.1175/1520-0493(1995)123&#60;0887:ATSO&#62;2.0.CO;2 }}</ref> and become most of the tropical cyclones in the Eastern Pacific basin.<ref name = "AOML FAQ A4">{{ cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: What is an easterly wave? | publisher = [[NOAA]] | accessdate = 2006-07-25 | url = http://www.aoml.noaa.gov/hrd/tcfaq/A4.html}}</ref><ref name="Landsea 1993">{{cite journal | author = [[Chris Landsea|Landsea, Chris]] | url = http://ams.allenpress.com/perlserv/?request=res-loc&uri=urn%3Aap%3Apdf%3Adoi%3A10.1175%2F1520-0493%281993%29121%3C1703%3AACOIMA%3E2.0.CO%3B2 | format = PDF | title = A Climatology of Intense (or Major) Atlantic Hurricanes | journal = [[Monthly Weather Review]] | volume = 121 | issue = 6 | year = 1993 | month = June | accessdate = 2006-03-25 | pages = 1703&ndash;1713 | doi = 10.1175/1520-0493(1993)121<1703:ACOIMA>2.0.CO;2 | doilabel = 10.1175/1520-0493(1993)121&#60;1703:ACOIMA&#62;2.0.CO;2}}</ref>

Tropical cyclones move westward when equatorward of the [[subtropical ridge]], intensifying as they move. Most of these systems form between 10 and 30&nbsp;degrees away of the [[equator]],<ref name=BOMmap>{{cite web | publisher = [[Bureau of Meteorology]] | url = http://www.bom.gov.au/bmrc/pubs/tcguide/ch1/figures_ch1/figure1.9.htm | title = Worldwide Tropical Cyclone Tracks 1979-88 | author = Neumann, Charles J. | work = Global Guide to Tropical Cyclone Forecasting | accessdate = 2006-12-12}}</ref> and 87% form no farther away than 20&nbsp;degrees of latitude, north or south.<ref>Henderson-Sellers, H. Zhang, G. Berz, K. Emanuel, [[William M. Gray|William Gray]], [[Christopher Landsea]], Greg Holland, J. Lighthill, S-L. Shieh, P. Webster, and K. McGuffie. [http://www.aoml.noaa.gov/hrd/Landsea/IPCC/index.html Tropical Cyclones and Global Climate Change: A Post-IPCC Assessment.] Retrieved on [[2008-02-25]].</ref> Because the [[Coriolis effect]] initiates and maintains tropical cyclone rotation, tropical cyclones rarely form or move within about 5&nbsp;degrees of the equator, where the Coriolis effect is weakest.<ref name=BOMmap>{{cite web | publisher = [[Bureau of Meteorology]] | url = http://www.bom.gov.au/bmrc/pubs/tcguide/ch1/figures_ch1/figure1.9.htm | title = Worldwide Tropical Cyclone Tracks 1979-88 | author = Neumann, Charles J. | work = Global Guide to Tropical Cyclone Forecasting | accessdate = 2006-12-12}}</ref> However, it is possible for tropical cyclones to form within this boundary as [[Tropical Storm Vamei]] did in 2001 and [[Cyclone Agni]] in 2004.<ref>{{cite web | publisher = Australian Severe Weather Index | author = Gary Padgett | title = Monthly Global Tropical Cyclone Summary, December 2001 | url = http://australiasevereweather.com/cyclones/2002/summ0112.htm}}</ref><ref>[[Joint Typhoon Warning Center]]. [https://metocph.nmci.navy.mil/jtwc/atcr/2004atcr/chapter1/chapter1_2.html 1.2 2004 North Indian Ocean Tropical Cyclones.] Retrieved on [[2008-02-24]].</ref>

==Movement and track==
===Steering winds===
Although tropical cyclones are large systems generating enormous energy, their movements over the Earth's surface are controlled by large-scale winds&mdash;the streams in the Earth's atmosphere. The path of motion is referred to as a tropical cyclone's ''track'' and has been analogized by Dr. Neil Frank, former director of the [[National Hurricane Center]], to "leaves carried along by a stream".<ref name = "AOML FAQ G6">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: What determines the movement of tropical cyclones?|publisher = [[NOAA]] | accessdate = 2006-07-25 | url = http://www.aoml.noaa.gov/hrd/tcfaq/G6.html}}</ref>

Tropical systems, while generally located [[equator]]ward of the 20th parallel, are steered primarily westward by the east-to-west winds on the equatorward side of the [[subtropical ridge]]—a persistent high pressure area over the world's oceans.<ref name = "AOML FAQ G6"/> In the tropical North Atlantic and Northeast Pacific oceans, [[trade winds]]—another name for the westward-moving wind currents—steer [[tropical waves]] westward from the [[Africa]]n coast and towards the Caribbean Sea, North America, and ultimately into the central Pacific ocean before the waves dampen out.<ref name = "AOML FAQ A4">{{ cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: What is an easterly wave? | publisher = [[NOAA]] | accessdate = 2006-07-25 | url = http://www.aoml.noaa.gov/hrd/tcfaq/A4.html}}</ref> These waves are the precursors to many tropical cyclones within this region.<ref name="MWR Avila 1995"/> In the Indian Ocean and Western Pacific (both north and south of the equator), tropical cyclogenesis is strongly influenced by the seasonal movement of the [[Intertropical Convergence Zone]] and the [[monsoon trough]], rather than by easterly waves.<ref name="MILLER7">{{cite web | author = DeCaria, Alex | publisher = [[Millersville University of Pennsylvania|Millersville University]] | url = http://snowball.millersville.edu/~adecaria/ESCI344/esci344_lesson05_TC_climatology.html | title = Lesson 5 – Tropical Cyclones: Climatology. | work = ESCI 344 – Tropical Meteorology | year = 2005 | accessdate = 2008-02-22}}</ref> Tropical cyclones can also be steered by other systems, such as other [[low pressure systems]], [[high pressure systems]], [[warm front|warm fronts]], and [[cold front|cold fronts]].

===Coriolis effect===
[[Image:Cyclone Monica.gif|thumb|250px|right|Infrared image of [[Cyclone Monica]] near peak intensity, showing [[clockwise]] rotation due to the [[Coriolis effect]]]]
The Earth's rotation imparts an acceleration known as the ''[[Coriolis effect]]'', ''Coriolis acceleration'', or colloquially, ''Coriolis force''. This acceleration causes cyclonic systems to turn towards the poles in the absence of strong steering currents.<ref name="Paleoglossary Cn-Cz">{{cite web | author = Baum, Steven K. | url = http://stommel.tamu.edu/~baum/paleo/paleogloss/node10.html | title = The Glossary: Cn-Cz. | work = Glossary of Oceanography and the Related Geosciences with References | publisher = [[Texas A&M University]] | date = [[January 20]], [[1997]] | accessdate = 2006-11-29}}</ref> The poleward portion of a tropical cyclone contains easterly winds, and the Coriolis effect pulls them slightly more poleward. The westerly winds on the equatorward portion of the cyclone pull slightly towards the equator, but, because the Coriolis effect weakens toward the equator, the net drag on the cyclone is poleward. Thus, tropical cyclones in the [[Northern Hemisphere]] usually turn north (before being blown east), and tropical cyclones in the [[Southern Hemisphere]] usually turn south (before being blown east) when no other effects counteract the Coriolis effect.<ref name="BritTCtrackcoriolis">[[Encyclopædia Britannica]]. [http://www.britannica.com/eb/article-247936/tropical-cyclone#849004.hook Tropical cyclone: Tropical cyclone tracks.] Retrieved on [[2008-02-25]].</ref>

The Coriolis effect also initiates cyclonic rotation, but it is not the driving force that brings this rotation to high speeds – that force is the [[heat of condensation]].<ref name="NOAA Question of the Month"/>

===Interaction with the mid-latitude westerlies===
[[Image:Ioke 2006 track.png|thumb|right|250 px|Storm track of [[Hurricane Ioke|Typhoon Ioke]], showing recurvature off the [[Japan]]ese coast in [[2006 Pacific hurricane season|2006]]]]
When a tropical cyclone crosses the [[subtropical ridge]] axis, its general track around the high-pressure area is deflected significantly by winds moving towards the general low-pressure area to its north. When the cyclone track becomes strongly poleward with an easterly component, the cyclone has begun ''recurvature.''<ref>U. S. Navy. [http://www.nrlmry.navy.mil/~chu/chap4/se200.htm Section 2: Tropical Cyclone Motion Terminology.] Retrieved on [[2007-04-10]].</ref> A typhoon moving through the Pacific Ocean towards Asia, for example, will recurve offshore of [[Japan]] to the north, and then to the northeast, if the typhoon encounters southwesterly winds (blowing northeastward) around a low-pressure system passing over [[China]] or [[Siberia]]. Many tropical cyclones are eventually forced toward the northeast by [[extratropical cyclone]]s in this manner, which move from west to east to the north of the subtropical ridge. An example of a tropical cyclone in recurvature was [[Hurricane Ioke|Typhoon Ioke]] in 2006, which took a similar trajectory.<ref name="CPHC Ioke">{{cite web | url = http://www.prh.noaa.gov/cphc/summaries/2006.php#ioke | title = Hurricane Ioke: 20-27 August 2006 | date = May 2007 | accessdate = 2007-06-09 | author = Powell, Jeff, et al. | work = 2006 Tropical Cyclones Central North Pacific | publisher = [[Central Pacific Hurricane Center]]}}</ref>

===Landfall===
{{see also|List of notable tropical cyclones|Tropical cyclogenesis#Unusual areas of formation|l2=Unusual areas of tropical cyclone formation}}
Officially, ''[[landfall (meteorology)|landfall]]'' is when a storm's center (the center of its circulation, not its edge) crosses the coastline.<ref name="NHC glossary"/> Storm conditions may be experienced on the coast and inland hours before landfall; in fact, a tropical cyclone can launch its strongest winds over land, yet not make landfall; if this occurs, then it is said that the storm made a ''direct hit'' on the coast.<ref name="NHC glossary"/> Due to this definition, the landfall area experiences half of a land-bound storm by the time the actual landfall occurs. For emergency preparedness, actions should be timed from when a certain wind speed or intensity of rainfall will reach land, not from when landfall will occur.<ref name="NHC glossary">{{cite web | author = [[National Hurricane Center]] | url = http://www.nhc.noaa.gov/aboutgloss.shtml | year = 2005 | title = Glossary of NHC/TPC Terms | accessdate= 2006-11-29 | publisher = [[National Oceanic and Atmospheric Administration]]}}</ref>

===Multiple storm interaction===
{{Main article|Fujiwhara effect}}
When two cyclones approach one another, their centers will begin orbiting cyclonically about a point between the two systems. The two vortices will be attracted to each other, and eventually spiral into the center point and merge. When the two vortices are of unequal size, the larger vortex will tend to dominate the interaction, and the smaller vortex will orbit around it. This phenomenon is called the Fujiwhara effect, after [[Sakuhei Fujiwhara]].<ref>{{cite web |url=http://www.usatoday.com/weather/wfujiwha.htm |title=Fujiwhara effect describes a stormy waltz |accessdate=2008-02-21 |work=[[USA Today]] |publisher= |date= }}</ref>

==Dissipation==
===Factors===
[[Image:TropicalStormFranklin05.jpg|thumb|right|250px|[[Tropical Storm Franklin (2005)|Tropical Storm Franklin]], an example of a strongly [[windshear|sheared]] tropical cyclone in the [[Atlantic hurricane|Atlantic Basin]] during [[2005 Atlantic hurricane season|2005]]]]
A tropical cyclone can cease to have tropical characteristics through several different ways. One such way is if it moves over land, thus depriving it of the warm water it needs to power itself, quickly losing strength.<ref>[[National Hurricane Center]]. [http://www.aoml.noaa.gov/hrd/tcfaq/C2.html Subject : C2) Doesn't the friction over land kill tropical cyclones?] Retrieved on [[2008-02-25]].</ref> Most strong storms lose their strength very rapidly after landfall and become disorganized areas of low pressure within a day or two, or evolve into [[extratropical cyclone]]s. While there is a chance a tropical cyclone could regenerate if it managed to get back over open warm water, if it remains over mountains for even a short time, weakening will accelerate.<ref>[[Bureau of Meteorology]]. [http://www.bom.gov.au/weather/wa/cyclone/about/inland_pilbara/index.shtml Tropical Cyclones Affecting Inland Pilbara towns.] Retrieved on [[2008-02-25]].</ref> Many storm fatalities occur in mountainous terrain, as the dying storm unleashes torrential rainfall,<ref>Yuh-Lang Lin, S. Chiao, J. A. Thurman, D. B. Ensley, and J. J. Charney. [http://ams.confex.com/ams/10Mountain/techprogram/paper_40695.htm Some Common Ingredients for heavy Orographic Rainfall and their Potential Application for Prediction.] Retrieved on [[2007-04-26]].</ref> leading to deadly [[flood]]s and [[mudslide]]s, similar to those that happened with [[Hurricane Mitch]] in 1998.<ref name="nhc">{{cite web|author=National Hurricane Center|year=1998|title=Hurricane Mitch Tropical Cyclone Report|accessdate=2006-04-20|url=http://www.nhc.noaa.gov/1998mitch.html NHC Mitch Report}}</ref> Additionally, dissipation can occur if a storm remains in the same area of ocean for too long, mixing the upper {{convert|60|m|ft}} of water, dropping sea surface temperatures more than 5&nbsp;°C (9&nbsp;°F).<ref>[[Joint Typhoon Warning Center]]. [http://www.nrlmry.navy.mil/~chu/chap2/se113.htm 1.13 Local Effects on the Observed Large-scale Circulations.] Retrieved on [[2008-02-25]].</ref> Without warm surface water, the storm cannot survive.<ref name="Shays et al 1989">{{cite journal | url = http://ams.allenpress.com/archive/1520-0485/19/5/pdf/i1520-0485-19-5-649.pdf | author = Shay, Lynn K., Russell L. Elsberry and Peter G. Black | title = Vertical Structure of the Ocean Current Response to a Hurricane | month = May | year = 1989 | accessdate = 2006-12-12 | format = PDF | journal = Journal of Physical Oceanography | volume = 19 | issue = 5 | doi = 10.1175/1520-0485(1989)019<0649:VSOTOC>2.0.CO;2 | pages = 649 | doilabel = 10.1175/1520-0485(1989)019&#60;0649:VSOTOC&#62;2.0.CO;2}}</ref>

A tropical cyclone can dissipate when it moves over waters significantly below {{convert|26.5|C|F}}. This will cause the storm to lose its tropical characteristics (i.e. thunderstorms near the center and warm core) and become a remnant low pressure area, which can persist for several days. This is the main dissipation mechanism in the Northeast Pacific ocean.<ref name="Edwards genesis">{{cite web | author = Edwards, Jonathan | url = http://www.hurricanezone.net/articles/tropical-cyclone-formation.html | title = Tropical Cyclone Formation | accessdate = 2006-11-30 | publisher = HurricaneZone.net}}</ref> Weakening or dissipation can occur if it experiences vertical [[wind shear]], causing the convection and heat engine to move away from the center; this normally ceases development of a tropical cyclone.<ref name="EAM">{{citebook|title=East Asian Monsoon |author= Chih-Pei Chang|year= 2004|publisher=World Scientific|id=ISBN 9812387692 |url=http://books.google.com/books?vid=ISBN9812387692&id=N8QYOdqGdgkC&pg=PA484&lpg=PA484&ots=jH3lLnS6LHie=ISO-8859-1&output=html&sig=Dxv5vz1f9RSR-VHJPygruiitADo}}</ref> Additionally, its interaction with the main belt of the Westerlies, by means of merging with a nearby frontal zone, can cause tropical cyclones to evolve into [[extratropical cyclones]]. This transition can take 1–3&nbsp;days.<ref name = "JWTC intensity">{{cite web | url = http://www.nrlmry.navy.mil/~chu/chap6/se300.htm | author = [[United States Naval Research Laboratory]] | work = Tropical Cyclone Forecasters' Reference Guide| title = Tropical Cyclone Intensity Terminology | accessdate = 2006-11-30 | date = [[September 23]], [[1999]]}}</ref> Even after a tropical cyclone is said to be extratropical or dissipated, it can still have tropical storm force (or occasionally hurricane/typhoon force) winds and drop several inches of rainfall. In the [[Pacific ocean]] and [[Atlantic ocean]], such tropical-derived cyclones of higher latitudes can be violent and may occasionally remain at hurricane or typhoon-force wind speeds when they reach the west coast of [[North America]]. These phenomena can also affect Europe, where they are known as ''[[European windstorm]]s''; [[Hurricane Iris (1995)|Hurricane Iris's]] extratropical remnants are an example of such a windstorm from 1995.<ref name="IrisTCR">{{cite web| author = Rappaport, Edward N. | url= http://www.nhc.noaa.gov/1995iris.html | title=Preliminary Report: Hurricane Iris: 22 August-4 September 1995 | publisher=[[National Hurricane Center]] | date=[[November 2]], [[2000]]|accessdate=2006-11-29}}</ref> Additionally, a cyclone can merge with another area of low pressure, becoming a larger area of low pressure. This can strengthen the resultant system, although it may no longer be a tropical cyclone.<ref name="EAM"/>

===Artificial dissipation===
In the 1960s and 1970s, the [[United States government]] attempted to weaken hurricanes through [[Project Stormfury]] by [[cloud seeding|seeding]] selected storms with [[silver iodide]]. It was thought that the seeding would cause [[supercooled water]] in the outer rainbands to freeze, causing the inner eyewall to collapse and thus reducing the winds.<ref>Hurricane Research Division. [http://www.aoml.noaa.gov/hrd/hrd_sub/sfury.html Project STORMFURY.] Retrieved on [[2008-02-25]].</ref> The winds of [[1969 Atlantic hurricane season#Hurricane Debbie|Hurricane Debbie]]—a hurricane seeded in Project Stormfury—dropped as much as 31%, but Debbie regained its strength after each of two seeding forays.<ref>H. E. Willoughby, D. P. Jorgensen, R. A. Black, and S. L. Rosenthal. [http://ams.allenpress.com/archive/1520-0477/66/5/pdf/i1520-0477-66-5-505.pdf Project Stormfury: A Scientific Chronicle 1962-1983.] Retrieved on [[2008-02-25]].</ref> In an earlier episode in 1947, disaster struck when a hurricane east of [[Jacksonville, Florida]] promptly changed its course after being seeded, and smashed into [[Savannah, Georgia]].<ref name="Whipple 151">{{cite book | author = Whipple, Addison | year = 1982 | title = Storm | pages = 151 | location = [[Alexandria, Virginia|Alexandria, VA]] | publisher = [[Time Life|Time Life Books]] | id = ISBN 0-8094-4312-0}}</ref> Because there was so much uncertainty about the behavior of these storms, the federal government would not approve seeding operations unless the hurricane had a less than 10% chance of making landfall within 48&nbsp;hours, greatly reducing the number of possible test storms. The project was dropped after it was discovered that [[eye (cyclone)#eyewall replacement cycles|eyewall replacement cycles]] occur naturally in strong hurricanes, casting doubt on the result of the earlier attempts. Today, it is known that silver iodide seeding is not likely to have an effect because the amount of supercooled water in the rainbands of a tropical cyclone is too low.<ref name = "AOML FAQ C5a">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: Why don't we try to destroy tropical cyclones by seeding them with silver iodide?|publisher = [[NOAA]] | accessdate = 2006-07-25 | url = http://www.aoml.noaa.gov/hrd/tcfaq/C5a.html}}</ref>

Other approaches have been suggested over time, including cooling the water under a tropical cyclone by towing [[iceberg]]s into the tropical oceans.<ref name = "AOML FAQ C5e"/> Other ideas range from covering the ocean in a substance that inhibits evaporation,<ref name = "AOML FAQ C5b">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: Why don't we try to destroy tropical cyclones by placing a substance on the ocean surface? |publisher = [[NOAA]] | accessdate = 2006-07-25 | url = http://www.aoml.noaa.gov/hrd/tcfaq/C5b.html}}</ref> dropping large quantities of ice into the eye at very early stages of development (so that the [[heat of condensation|latent heat]] is absorbed by the ice, instead of being converted to kinetic energy that would feed the positive feedback loop),<ref name = "AOML FAQ C5e">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: Why don't we try to destroy tropical cyclones by cooling the surface waters with icebergs or deep ocean water? |publisher = [[NOAA]] | accessdate = 2006-07-25 | url = http://www.aoml.noaa.gov/hrd/tcfaq/C5e.html}}</ref> or blasting the cyclone apart with nuclear weapons.<ref name = "AOML FAQ C5c">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: Why don't we try to destroy tropical cyclones by nuking them? |publisher = [[NOAA]] | accessdate = 2006-07-25 | url = http://www.aoml.noaa.gov/hrd/tcfaq/C5c.html}}</ref> Project Cirrus even involved throwing dry ice on a cyclone.<ref name="Sudden Sea">{{cite book | author = Scotti, R. A. | title = Sudden Sea: the Great Hurricane of 1938 | year = 2003 | pages=47 | edition = 1st ed. | publisher = Little, Brown, and Company | id = ISBN 0-316-73911-1}}</ref> These approaches all suffer from one flaw above many others: tropical cyclones are simply too large for any of the weakening techniques to be practical.<ref name = "AOML FAQ C5f">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: Why do not we try to destroy tropical cyclones by (fill in the blank)?|publisher = [[NOAA]] | accessdate = 2006-07-25 | url = http://www.aoml.noaa.gov/hrd/tcfaq/C5i.html}}</ref>

==Effects==
[[Image:Hurricane katrina damage gulfport mississippi.jpg|thumb|250px|right|The aftermath of [[Hurricane Katrina]] in [[Gulfport, Mississippi]]. Katrina was the costliest tropical cyclone in United States history.]]
{{main|Effects of tropical cyclones}}
Tropical cyclones out at sea cause large waves, heavy rain, and high winds, disrupting international shipping and, at times, causing shipwrecks.<ref name="18cva">{{cite web|author=David Roth and Hugh Cobb|year=2001|title=Eighteenth Century Virginia Hurricanes|publisher=NOAA|accessdate=2007-02-24|url=http://www.hpc.ncep.noaa.gov/research/roth/va18hur.htm}}</ref> Tropical cyclones stir up water, leaving a cool wake behind them,<ref name="NASA Cooling"/> which causes the region to be less favourable for subsequent tropical cyclones. On land, strong [[wind]]s can damage or destroy vehicles, buildings, bridges, and other outside objects, turning loose debris into deadly flying projectiles. The [[storm surge]], or the increase in sea level due to the cyclone, is typically the worst effect from landfalling tropical cyclones, historically resulting in 90% of tropical cyclone deaths.<ref name="oxfo">{{cite web|author=James M. Shultz, Jill Russell and Zelde Espinel|year=2005|title=Epidemiology of Tropical Cyclones: The Dynamics of Disaster, Disease, and Development|publisher=Oxford Journal|accessdate=2007-02-24|url=http://epirev.oxfordjournals.org/cgi/content/full/27/1/21}}</ref>
The broad rotation of a landfalling tropical cyclone, and vertical wind shear at its periphery, spawns [[History of tropical cyclone-spawned tornadoes|tornadoes]]. Tornadoes can also be spawned
as a result of [[Eye (cyclone)#Eyewall mesovortices|eyewall mesovortices]], which persist until landfall.<ref name = "AOML FAQ L6">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: Are TC tornadoes weaker than midlatitude tornadoes?|publisher = [[NOAA]] | accessdate = 2006-07-25 | url = http://www.aoml.noaa.gov/hrd/tcfaq/L6.html}}</ref>

Over the past two centuries, tropical cyclones have been responsible for the deaths of about 1.9&nbsp;million persons worldwide. Large areas of standing water caused by flooding lead to infection, as well as contributing to mosquito-borne illnesses. Crowded evacuees in [[shelter]]s increase the risk of disease propagation.<ref name="Shultz Epid Reviews 2005"/> Tropical cyclones significantly interrupt infrastructure, leading to power outages, bridge destruction, and the hampering of reconstruction efforts.<ref name="Shultz Epid Reviews 2005"/><ref name="Power failures">{{cite news|author=Staff Writer|date=2005-08-30|title=Hurricane Katrina Situation Report #11|publisher=Office of Electricity Delivery and Energy Reliability (OE) [[United States Department of Energy]]| accessdate=2007-02-24 |url=http://www.oe.netl.doe.gov/docs/katrina/katrina_083005_1600.pdf | format = PDF}}</ref>

Although cyclones take an enormous toll in lives and personal property, they may be important factors in the [[precipitation (meteorology)|precipitation]] regimes of places they impact, as they may bring much-needed precipitation to otherwise dry regions.<ref name="2005 EPac outlook">[[National Oceanic and Atmospheric Administration]]. [http://www.cpc.ncep.noaa.gov/products/Epac_hurr/Epac_hurricane.html 2005 Tropical Eastern North Pacific Hurricane Outlook.] Retrieved on [[2006-05-02]].</ref> Tropical cyclones also help maintain the global heat balance by moving warm, moist tropical air to the [[middle latitudes]] and polar regions.<ref name="Zurich">{{cite web | publisher = Zurich Financial Services | url = http://www.zurich.com/main/productsandsolutions/industryinsight/2005/july2005/industryinsight20050711_004.htm | title = Living With an Annual Disaster | date = July/August 2005 | accessdate = 2006-11-29}}</ref> The storm surge and winds of hurricanes may be destructive to human-made structures, but they also stir up the waters of coastal [[estuary|estuaries]], which are typically important fish breeding locales. Tropical cyclone destruction spurs redevelopment, greatly increasing local property values.<ref name="Christopherson">{{cite book | author = Christopherson, Robert W. | date = 1992 | title = Geosystems: An Introduction to Physical Geography | pages = 222–224 | publisher = Macmillan Publishing Company | location = [[New York City|New York]] | id = ISBN 0-02-322443-6}}</ref>

==Observation and forecasting==
===Observation===
{{main|Tropical cyclone observation}}
[[Image:Isidore091902-p3sunset.jpg|right|thumb|250px|Sunset view of [[Hurricane Isidore]]'s rainbands photographed at {{convert|7000|ft|m}}]]
Intense tropical cyclones pose a particular observation challenge, as they are a dangerous oceanic phenomenon, and [[weather station]]s, being relatively sparse, are rarely available on the site of the storm itself. Surface observations are generally available only if the storm is passing over an island or a coastal area, or if there is a nearby ship. Usually, real-time measurements are taken in the periphery of the cyclone, where conditions are less catastrophic and its true strength cannot be evaluated. For this reason, there are teams of meteorologists that move into the path of tropical cyclones to help evaluate their strength at the point of landfall.<ref name="FCMP">{{cite web | url = http://users.ce.ufl.edu/~fcmp/overview/overview.htm | author = Florida Coastal Monitoring Program | title = Project Overview | accessdate = 2006-03-30 | publisher = [[University of Florida]]}}</ref>

Tropical cyclones far from land are tracked by [[weather satellite]]s capturing [[visible light|visible]] and [[infrared]] images from space, usually at half-hour to quarter-hour intervals. As a storm approaches land, it can be observed by land-based [[Pulse-Doppler radar|Doppler]] [[weather radar|radar]]. Radar plays a crucial role around landfall by showing a storm's location and intensity every several minutes.<ref name="CPHC">Central Pacific Hurricane Center. [http://www.prh.noaa.gov/cphc/HAW/observations.php Observations.] Retrieved on [[2006-12-09]].</ref>

[[In-situ]] measurements, in real-time, can be taken by sending specially equipped reconnaissance flights into the cyclone. In the Atlantic basin, these flights are regularly flown by United States government [[hurricane hunters]].<ref name="Hurricane Hunters">{{cite web | author = 403rd Wing | url = http://www.hurricanehunters.com | title = The Hurricane Hunters | publisher = [[Hurricane Hunters|53rd Weather Reconnaissance Squadron]] | accessdate = 2006-03-30}}</ref> The aircraft used are [[WC-130]] Hercules and [[WP-3D]] Orions, both four-engine [[turboprop]] cargo aircraft. These aircraft fly directly into the cyclone and take direct and remote-sensing measurements. The aircraft also launch [[GPS dropsonde]]s inside the cyclone. These sondes measure temperature, humidity, pressure, and especially winds between flight level and the ocean's surface. A new era in hurricane observation began when a remotely piloted [[Insitu Aerosonde|Aerosonde]], a small drone aircraft, was flown through Tropical Storm Ophelia as it passed Virginia's Eastern Shore during the 2005 hurricane season. A similar mission was also completed successfully in the western Pacific ocean. This demonstrated a new way to probe the storms at low altitudes that human pilots seldom dare.<ref name="SunHerald">{{cite news | author = Lee, Christopher | title = Drone, Sensors May Open Path Into Eye of Storm | url = http://www.washingtonpost.com/wp-dyn/content/article/2007/10/07/AR2007100700971_pf.html | publisher = [[The Washington Post]] | accessdate = 2008-02-22}}</ref>

[[Image:NHC Atlantic Forecast Error Trends.png|thumb|right|250px|A general decrease in error trends in tropical cyclone path prediction is evident since the 1970s]]

===Forecasting===
{{seealso|Tropical cyclone track forecasting|Tropical cyclone prediction model|Tropical cyclone rainfall forecasting}}
Because of the forces that affect tropical cyclone tracks, accurate track predictions depend on determining the position and strength of high- and low-pressure areas, and predicting how those areas will change during the life of a tropical system. The deep layer mean flow, or average wind through the depth of the [[troposphere]], is considered the best tool in determining track direction and speed. If storms are significantly sheared, use of wind speed measurements at a lower altitude, such as at the 700&nbsp;[[mbar|hPa]] pressure surface ({{convert|3000|m|ft|abbr=off|lk=off|disp=s}} above sea level) will produce better predictions. Tropical forecasters also consider smoothing out short-term wobbles of the storm as it allows them to determine a more accurate long-term trajectory.<ref>{{cite web | author = [[United States Navy]] | url = http://www.nrlmry.navy.mil/~chu/chap4/se100.htm | title = Influences on Tropical Cyclone Motion | accessdate = 2007-04-10}}</ref> High-speed computers and sophisticated simulation software allow forecasters to produce [[tropical cyclone prediction model|computer models]] that predict tropical cyclone tracks based on the future position and strength of high- and low-pressure systems. Combining forecast models with increased understanding of the forces that act on tropical cyclones, as well as with a wealth of data from Earth-orbiting satellites and other sensors, scientists have increased the accuracy of track forecasts over recent decades.<ref name="NHC forecast verifications models">{{cite web | author = [[National Hurricane Center]] | url = http://www.nhc.noaa.gov/verification/verify6.shtml?#FIG1 | work = National Hurricane Center Forecast Verification | title = Annual average model track errors for Atlantic basin tropical cyclones for the period 1994-2005, for a homogeneous selection of "early" models | accessdate = 2006-11-30 | publisher = [[National Oceanic and Atmospheric Administration]] | date = [[May 22]], [[2006]]}}</ref> However, scientists are less skillful at predicting the intensity of tropical cyclones.<ref name="NHC forecast verifications Atlantic">{{cite web | author = [[National Hurricane Center]] | work = National Hurricane Center Forecast Verification | url = http://www.nhc.noaa.gov/verification/verify5.shtml? | title = Annual average official track errors for Atlantic basin tropical cyclones for the period 1989-2005, with least-squares trend lines superimposed | accessdate = 2006-11-30 | publisher = [[National Oceanic and Atmospheric Administration]] | date = [[May 22]], [[2006]]}}</ref> The lack of improvement in intensity forecasting is attributed to the complexity of tropical systems and an incomplete understanding of factors that affect their development.

==Classifications, terminology, and naming==
===Intensity classifications===
{{main|Tropical cyclone scales}}
[[Image:Typhoon saomai 060807.jpg|thumb|right|250px|Three tropical cyclones at different stages of development. The weakest (left), demonstrates only the most basic circular shape. A stronger storm (top right) demonstrates [[rainbands|spiral banding]] and increased centralization, while the strongest (lower right) has developed an [[eye (cyclone)|eye]].]]
Tropical cyclones are classified into three main groups, based on intensity: tropical depressions, tropical storms, and a third group of more intense storms, whose name depends on the region. For example, if a [[#Tropical storm|tropical storm]] in the Northwestern Pacific reaches hurricane-strength winds on the [[Beaufort scale]], it is referred to as a ''typhoon''; if a tropical storm passes the same benchmark in the [[Pacific hurricane|Northeast Pacific Basin]], or in [[Atlantic hurricane|the Atlantic]], it is called a ''hurricane''.<ref name="NHC glossary"/> Neither "hurricane" nor "typhoon" are used in either the Southern Hemisphere or the Indian Ocean. In these [[Tropical cyclone basins|basins]], storms of tropical nature are referred as simply "cyclones".

Additionally, as indicated in the table below, each basin uses a separate [[Tropical cyclone scales|system of terminology]], making comparisons between different basins difficult. In the Pacific Ocean, hurricanes from the Central North Pacific sometimes cross the [[International Date Line]] into the Northwest Pacific, becoming typhoons (such as [[Hurricane Ioke|Hurricane/Typhoon Ioke]] in 2006); on rare occasions, the reverse will occur.<ref name="CPHC John TCR">{{cite web | author=[[Central Pacific Hurricane Center]] | title=Hurricane John Preliminary Report | publisher=[[National Oceanic and Atmospheric Administration]] | url=http://www.prh.noaa.gov/cphc/summaries/1994.php#John | year= 2004 | accessdate=2007-03-23}}</ref> It should also be noted that typhoons with sustained winds greater than {{convert|67|m/s|kn}} or {{convert|150|mph|km/h}} are called ''Super Typhoons'' by the Joint Typhoon Warning Center.<ref name="SUPERDUPER">{{cite web | author = Bouchard, R. H. | url = http://metocph.nmci.navy.mil/jtwc/pubref/References/where_have_all_the_super_typhoons_gone.ppt | title = A Climatology of Very Intense Typhoons: Or Where Have All the Super Typhoons Gone? | format = [[Microsoft PowerPoint|PPT]] | accessdate = 2006-12-05 | date = April 1990}}</ref>

==== Tropical depression ====
A '''tropical depression''' is an organized system of clouds and thunderstorms with a defined, closed surface circulation and [[maximum sustained wind]]s of less than {{convert|17|m/s|kn}} or {{convert|39|mph|km/h}}. It has no [[eye (cyclone)|eye]] and does not typically have the organization or the spiral shape of more powerful storms. However, it is already a low-pressure system, hence the name "depression".<ref name = "NOAA preparedness"/> The practice of the [[Philippines]] is to name tropical depressions from their own naming convention when the depressions are within the Philippines' area of responsibility.<ref name="AOML FAQ B2">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: What are the upcoming tropical cyclone names? | publisher = [[NOAA]] | accessdate = 2006-12-11 | url = http://www.aoml.noaa.gov/hrd/tcfaq/B2.html}}</ref>

==== Tropical storm ====
A '''tropical storm''' is an organized system of strong thunderstorms with a defined surface circulation and maximum sustained winds between {{convert|17|m/s|kn}} ({{convert|39|mph|km/h}}) and {{convert|32|m/s|kn}} ({{convert|73|mph|km/h}}). At this point, the distinctive cyclonic shape starts to develop, although an eye is not usually present. Government weather services, other than the Philippines, first assign names to systems that reach this intensity (thus the term ''named storm'').<ref name = "NOAA preparedness"/>

==== Hurricane or typhoon ====
A '''hurricane''' or '''typhoon''' (sometimes simply referred to as a tropical cyclone, as opposed to a depression or storm) is a system with sustained winds of at least {{convert|33|m/s|kn}} or {{convert|74|mph|km/h}}.<ref name = "NOAA preparedness"/> A cyclone of this intensity tends to develop an eye, an area of relative calm (and lowest atmospheric pressure) at the center of circulation. The eye is often visible in satellite images as a small, circular, cloud-free spot. Surrounding the eye is the [[eyewall]], an area about {{convert|16|km|mi}} to {{convert|80|km|mi}} wide in which the strongest [[thunderstorm]]s and winds circulate around the storm's center. Maximum sustained winds in the strongest tropical cyclones have been estimated at about {{convert|85|m/s|kn}} or {{convert|195|mph|km/h}}.<ref name = "AOML FAQ E1"/>
{| class=wikitable style="font-size:92%;"
! colspan=9 style="background: #ccf;" | '''Tropical Cyclone Classifications (all winds are 10-minute averages)'''<ref>[[National Hurricane Center]]. [http://www.aoml.noaa.gov/hrd/tcfaq/A1.html Subject: A1) What is a hurricane, typhoon, or tropical cyclone?] Retrieved on [[2008-02-25]].</ref><ref>[[Bureau of Meteorology]]. [http://www.bom.gov.au/bmrc/pubs/tcguide/ch1/ch1_3.htm Global Guide to Tropical Cyclone Forecasting] Retrieved on [[2008-02-25]].</ref>
|-
! [[Beaufort scale]]
! 10-minute sustained winds ([[Knot (speed)|knot]]s)
! N Indian Ocean<br />[[Indian Meteorological Department|IMD]]
! SW Indian Ocean<br />[[Météo-France|MF]]
! Australia<br />[[Bureau of Meteorology (Australia)|BOM]]
! SW Pacific<br />[[Fiji Meteorological Service|FMS]]
! NW Pacific<br />[[Japan Meteorological Agency|JMA]]
! NW Pacific<br />[[Joint Typhoon Warning Center|JTWC]]
! NE Pacific &<br />N Atlantic<br />[[National Hurricane Center|NHC]], [[Canadian Hurricane Centre|CHC]] & [[Central Pacific Hurricane Center|CPHC]]
|-
| 0–6
| <28
| Depression
| Trop. Disturbance
|rowspan="3" | Tropical Low
|rowspan="3" | Tropical Depression
|rowspan="3" | Tropical Depression
|rowspan="2" | Tropical Depression
|rowspan="2" | Tropical Depression
|-
|rowspan="2" | 7
| 28–29
|rowspan="2" | Deep Depression
|rowspan="2" | Depression
|-
| 30–33
|rowspan="3" | Tropical Storm
|rowspan="3" | Tropical Storm
|-
| 8–9
| 34–47
| Cyclonic Storm
| Moderate Tropical Storm
| Tropical Cyclone (1)
| Tropical Cyclone (1)
| Tropical Storm
|-
| 10
| 48–55
|rowspan="2" | Severe Cyclonic Storm
|rowspan="2" | Severe Tropical Storm
|rowspan="2" | Tropical Cyclone (2)
|rowspan="2" | Tropical Cyclone (2)
|rowspan="2" | Severe Tropical Storm
|-
| 11
| 56–63
|rowspan="7" | Typhoon
|rowspan="2" | Hurricane (1)
|-
|rowspan="8" | 12
| 64–72
|rowspan="7" | Very Severe Cyclonic Storm
|rowspan="3" | Tropical Cyclone
|rowspan="2" | Severe Tropical Cyclone (3)
|rowspan="2" | Severe Tropical Cyclone (3)
|rowspan="8" | Typhoon
|-
| 73–85
| Hurricane (2)
|-
| 86–89
|rowspan="3" | Severe Tropical Cyclone (4)
|rowspan="3" | Severe Tropical Cyclone (4)
|rowspan="2" | Major Hurricane (3)
|-
| 90–99
|rowspan="3" | Intense Tropical Cyclone
|-
| 100–106
|rowspan="3" | Major Hurricane (4)
|-
| 107–114
|rowspan="3" | Severe Tropical Cyclone (5)
|rowspan="3" | Severe Tropical Cyclone (5)
|-
| 115–119
|rowspan="2" | Very Intense Tropical Cyclone
|rowspan="2" | Super Typhoon
|-
| >120
| Super Cyclonic Storm
| Major Hurricane (5)
|}

===Origin of storm terms===
[[Image:101.typhoon.altonthompson.jpg|thumb|250px| [[Taipei 101]] endures a typhoon in 2005]]The word ''typhoon'', used today in the Northwest Pacific, may be derived from [[Urdu language|Urdu]], [[Persian language|Persian]] and [[Arabic language|Arabic]] ''ţūfān'' (طوفان), which in turn originates from [[Greek language|Greek]] ''[[Typhon|tuphōn]]'' (Τυφών), a monster in [[Greek mythology]] responsible for hot winds.<ref name="Greek typhoon">{{cite encyclopedia | encyclopedia = [[The American Heritage Dictionary of the English Language]] | year = 2004 | publisher = [[Dictionary.com]] | url = http://dictionary.reference.com/browse/typhoon | accessdate = 2006-12-14 | title = Typhoon | edition = 4th ed.}}</ref> The related [[Portuguese language|Portuguese]] word ''tufão'', used in Portuguese for typhoons, is also derived from Greek ''tuphōn''.<ref>{{cite web|url = http://www.crid.or.cr/crid/ESP/sistregio/vocabulario/Listado%20Alfab%E9tico%20de%20T%E9rminos%20Eng..pdf
| work = Centro Regional de Información sobre Desastres |language = English, Spanish, Portuguese and French | title = Disaster Controlled Vocabulary (VDC) | accessdate = 2008-01-24| format = PDF}}</ref>

The word ''hurricane'', used in the North Atlantic and Northeast Pacific, is derived from the name of a native [[Caribbean]] [[Amerindian]] storm [[god]], [[Huracan]], via [[Spanish language|Spanish]] ''huracán''.<ref name = "AOML FAQ B4">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: What is the origin of the word "hurricane"?|publisher = [[NOAA]] | accessdate = 2006-07-25 | url = http://www.aoml.noaa.gov/hrd/tcfaq/B4.html}}</ref> (Huracan is also the source of the word ''Orcan'', another word for the [[European windstorm]]. These events should not be confused.) Huracan became the Spanish term for hurricanes.

===Naming===
{{main|Tropical cyclone naming|Lists of tropical cyclone names}}
Storms reaching tropical storm strength were initially given names to eliminate confusion when there are multiple systems in any individual basin at the same time, which assists in warning people of the coming storm.<ref>National Hurricane Center. [http://www.nhc.noaa.gov/aboutnames.shtml Worldwide Tropical Cyclone Names.] Retrieved on [[2006-12-28]].</ref> In most cases, a tropical cyclone retains its name throughout its life; however, under [[Tropical cyclone naming#Renaming of tropical cyclones|special circumstances]], tropical cyclones may be renamed while active. These names are taken from lists that vary from region to region and are drafted a few years ahead of time. The lists are decided on, depending on the regions, either by committees of the [[World Meteorological Organization]] (called primarily to discuss many other issues), or by national weather offices involved in the forecasting of the storms. Each year, the names of particularly destructive storms (if there are any) are "retired" and new names are chosen to take their place.

==Notable tropical cyclones==
{{main|List of notable tropical cyclones|List of Atlantic hurricanes|List of Pacific hurricanes}}
Tropical cyclones that cause extreme destruction are rare, although when they occur, they can cause great amounts of damage or thousands of fatalities.

The [[1970 Bhola cyclone]] is the deadliest tropical cyclone on record, killing more than 300,000&nbsp;people<ref name="faqe9">{{cite web|author=Chris Landsea|year=1993|title=Which tropical cyclones have caused the most deaths and most damage?|publisher=Hurricane Research Division|accessdate=2007-02-23|url=http://www.aoml.noaa.gov/hrd/tcfaq/E9.html}}</ref> and potentially as many as 1&nbsp;million<ref name="1970death">{{cite news|author=Lawson|year=1999|title=South Asia: A history of destruction|publisher=[[BBC|British Broadcasting Corporation]]|accessdate=2007-02-23|url=http://news.bbc.co.uk/1/hi/world/south_asia/503139.stm}}</ref> after striking the densely populated [[Ganges Delta]] region of [[Bangladesh]] on [[November 13]], [[1970]]. Its powerful storm surge was responsible for the high death toll.<ref name="faqe9"/> The [[List of North Indian Ocean cyclone seasons|North Indian cyclone basin]] has historically been the deadliest basin, with several cyclones since 1900 killing more than 100,000&nbsp;people, all in Bangladesh.<ref name="Shultz Epid Reviews 2005">{{cite journal | author = Shultz, James M., Jill Russell and Zelde Espinel | title = Epidemiology of Tropical Cyclones: The Dynamics of Disaster, Disease, and Development | journal = Epidemiologic Reviews | volume = 27 | issue = 1 | pages = 21–25 | url = http://epirev.oxfordjournals.org/cgi/content/full/27/1/21 | date = July 2005 | accessdate=2006-12-14 | doi = 10.1093/epirev/mxi011 | pmid = 15958424}}</ref><ref name="Deadliest cyclone">{{cite journal | author = Frank, Neil L. and S. A. Husain | title = The Deadliest Tropical Cyclone in History | date = June 1971 | url = http://ams.allenpress.com/archive/1520-0477/52/6/pdf/i1520-0477-52-6-438.pdf | format = PDF | journal = Bulletin of the American Meteorological Society | volume = 52 | issue = 6 | pages = 438–445 | accessdate = 2006-12-14 | doi = 10.1175/1520-0477(1971)052<0438:TDTCIH>2.0.CO;2 | doilabel = 10.1175/1520-0477(1971)052&#60;0438:TDTCIH&#62;2.0.CO;2 | year = 1971}}</ref> Elsewhere, [[Typhoon Nina (1975)|Typhoon Nina]] killed nearly 100,000 in [[China]] due to a [[100-year flood|2000-year flood]] that caused 62&nbsp;dams including the [[Banqiao Dam]] to fail.<ref>Linda J. Anderson-Berry. [http://www.aoml.noaa.gov/hrd/iwtc/AndersonBerry5-1.html Fifth International Workshop on Tropycal Cyclones: Topic 5.1: Societal Impacts of Tropical Cyclones.] Retrieved on [[2008-02-26]].</ref> The [[Great Hurricane of 1780]] is the deadliest [[Atlantic hurricane]] on record, killing about 22,000&nbsp;people in the [[Lesser Antilles]].<ref name=NHCPastDeadly>{{cite web | author = [[National Hurricane Center]] | url = http://www.nhc.noaa.gov/pastdeadlyapp1.shtml? | title = The Deadliest Atlantic Tropical Cyclones, 1492-1996 | accessdate = 2006-03-31 | date = [[April 22]], [[1997]] | publisher = [[National Oceanic and Atmospheric Administration]]}}</ref> A tropical cyclone does need not be particularly strong to cause memorable damage, primarily if the deaths are from rainfall or mudslides. [[Tropical Storm Thelma]] in November 1991 killed thousands in the [[Philippines]],<ref name="JTWCThelma">{{cite web | url = https://metocph.nmci.navy.mil/jtwc/atcr/1991atcr/pdf/wnp/27w.pdf | title = Typhoon Thelma (27W) | accessdate = 2006-03-31 | author = [[Joint Typhoon Warning Center]] | work = 1991 Annual Tropical Cyclone Report | format = PDF}}</ref> while in 1982, the unnamed tropical depression that eventually became [[Hurricane Paul (1982)|Hurricane Paul]] killed around 1,000&nbsp;people in [[Central America]].<ref name="MWR Paul 1982">{{cite journal | author = Gunther, E. B., R.L. Cross, and R.A. Wagoner | title = Eastern North Pacific Tropical Cyclones of 1982 | url = http://ams.allenpress.com/archive/1520-0493/111/5/pdf/i1520-0493-111-5-1080.pdf | month = May | year = 1983 | journal = [[Monthly Weather Review]] | format = PDF | volume = 111 | issue = 5 | accessdate = 2006-03-31 | doi = 10.1175/1520-0493(1983)111<1080:ENPTCO>2.0.CO;2 | pages = 1080 | doilabel = 10.1175/1520-0493(1983)111&#60;1080:ENPTCO&#62;2.0.CO;2}}</ref>

[[Hurricane Katrina]] is estimated as the costliest tropical cyclone worldwide,<ref name="epi">{{cite web|author=Earth Policy Institute|year=2006|title=Hurricane Damages Sour to New Levels|publisher=United States Department of Commerce|accessdate=2007-02-23|url=http://www.earth-policy.org/Updates/2006/Update58_data.htm}}</ref> causing $81.2&nbsp;billion in property damage (2005&nbsp;USD)<ref name="KatrinaTCR">{{cite web|author = Knabb, Richard D., Jamie R. Rhome and Daniel P. Brown | url=http://www.nhc.noaa.gov/pdf/TCR-AL122005_Katrina.pdf | format=PDF | title=Tropical Cyclone Report: Hurricane Katrina: 23-30 August 2005 | publisher=[[National Hurricane Center]] | date=[[December 20]], [[2005]] | accessdate=2006-05-30}}</ref> with overall damage estimates exceeding $100&nbsp;billion (2005&nbsp;USD).<ref name="epi"/> Katrina killed at least 1,836&nbsp;people after striking [[Louisiana]] and [[Mississippi]] as a [[tropical cyclone scales|major hurricane]] in August 2005.<ref name="KatrinaTCR"/> The [[Galveston Hurricane of 1900]] is the deadliest natural disaster in the United States, killing an estimated 6,000 to 12,000&nbsp;people in [[Galveston, Texas]].<ref>[[National Hurricane Center]]. [http://www.nhc.noaa.gov/HAW2/english/history.shtml#galveston Galveston Hurricane 1900.] Retrieved on [[2008-02-24]].</ref> [[Hurricane Iniki]] in 1992 was the most powerful storm to strike [[Hawaii]] in recorded history, hitting [[Kauai]] as a Category&nbsp;4 hurricane, killing six people, and causing U.S. $3&nbsp;billion in damage.<ref name="InikiTCR">{{cite web|publisher = [[National Oceanic and Atmospheric Administration]] | url= http://www.prh.noaa.gov/cphc/summaries/1992.php#Iniki | title=Hurricane Iniki Natural Disaster Survey Report |author=[[Central Pacific Hurricane Center]]| accessdate=2006-03-31}}</ref> Other destructive Eastern [[Pacific hurricane]]s include [[Hurricane Pauline|Pauline]] and [[Hurricane Kenna|Kenna]], both causing severe damage after striking [[Mexico]] as major hurricanes.<ref name="PaulineTCR">{{cite web | last=Lawrence | first=Miles B. | url=http://www.nhc.noaa.gov/1997pauline.html | title=Preliminary Report: Hurricane Pauline: 5-10 October 1997 | publisher=[[National Hurricane Center]] | date=[[November 7]], [[1997]] | accessdate=2006-03-31}}</ref><ref name="KennaTCR">{{cite web | author = [[James Franklin (meteorologist)|Franklin, James L]]. | url=http://www.nhc.noaa.gov/2002kenna.shtml | title=Tropical Cyclone Report: Hurricane Kenna: 22-26 October 2002 | publisher=[[National Hurricane Center]] | date=[[December 26]], [[2002]] | accessdate=2006-03-31}}</ref> In March 2004, [[Cyclone Gafilo]] struck northeastern [[Madagascar]] as a powerful cyclone, killing 74, affecting more than 200,000, and becoming the worst cyclone to affect the nation for more than 20&nbsp;years.<ref name="gafilo">{{cite web|author=World Food Programme|year=2004|title=WFP Assists Cyclone And Flood Victims in Madagascar|accessdate=2007-02-24|url=http://www.sidsnet.org/archives/other-newswire/2004/msg00182.html}}</ref>

[[Image:Typhoonsizes.jpg|right|frame|The relative sizes of [[Typhoon Tip]], [[Cyclone Tracy]], and the United States]]
The most intense storm on record was [[Typhoon Tip]] in the northwestern Pacific Ocean in 1979, which reached a minimum pressure of 870&nbsp;[[millibar|mbar]] (25.69&nbsp;[[inHg]]) and maximum sustained wind speeds of {{convert|165|kn|m/s}} or {{convert|190|mph|km/h}}.<ref name="jtwc">{{cite web | author=George M. Dunnavan & John W. Dierks | year=1980 | title=An Analysis of Super Typhoon Tip (October 1979) | publisher=Joint Typhoon Warning Center | accessdate=2007-01-24| format = PDF | url=http://ams.allenpress.com/archive/1520-0493/108/11/pdf/i1520-0493-108-11-1915.pdf}}</ref> [[Tip]], however, does not solely hold the record for fastest sustained winds in a cyclone. [[1997 Pacific typhoon season#Super Typhoon Keith|Typhoon Keith]] in the Pacific and Hurricanes [[Hurricane Camille|Camille]] and [[Hurricane Allen|Allen]] in the North Atlantic currently share this record with Tip.<ref name="Weathermatrix Mitch">{{cite web | author = Ferrell, Jesse | publisher = Weathermatrix.net | url = http://www.weathermatrix.net/tropical/1998/13/mitch.html | title = Hurricane Mitch | accessdate = 2006-03-30 | date = [[October 26]], [[1998]]}}</ref> Camille was the only storm to actually strike land while at that intensity, making it, with {{convert|165|kn|m/s}} or {{convert|190|mph|km/h}} sustained winds and {{convert|183|kn|m/s}} or {{convert|210|mph|km/h}} gusts, the strongest tropical cyclone on record at landfall.<ref name="hurdat">{{cite web|author=NHC Hurricane Research Division|date=2006-02-17|title=Atlantic hurricane best track ("HURDAT")|publisher=NOAA|accessdate=2007-02-22|url=http://www.aoml.noaa.gov/hrd/hurdat/easyhurdat_5105.html#0_0}}</ref> [[Typhoon Nancy (1961)|Typhoon Nancy]] in 1961 had recorded wind speeds of {{convert|185|kn|m/s}} or {{convert|215|mph|km/h}}, but recent research indicates that wind speeds from the 1940s to the 1960s were gauged too high, and this is no longer considered the storm with the highest wind speeds on record.<ref name = "AOML FAQ E1">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: Which is the most intense tropical cyclone on record? | publisher = [[NOAA]] | accessdate = 2006-07-25|url = http://www.aoml.noaa.gov/hrd/tcfaq/E1.html}}</ref> Similarly, a surface-level gust caused by [[Typhoon Paka]] on [[Guam]] was recorded at {{convert|205|kn|m/s}} or {{convert|235|mph|km/h}}. Had it been confirmed, it would be the strongest non-[[tornado|tornadic]] wind ever recorded on the Earth's surface, but the reading had to be discarded since the [[anemometer]] was damaged by the storm.<ref name="NWSPaka">{{cite web | author = Houston, Sam, Greg Forbes and Arthur Chiu | publisher = [[National Weather Service]] | date = [[17 August]], [[1998]] | url = http://www.aoml.noaa.gov/hrd/project98/sh_proj1.html | title = Super Typhoon Paka's (1997) Surface Winds Over Guam | accessdate = 2006-03-30}}</ref>

In addition to being the most intense tropical cyclone on record, Tip was the largest cyclone on record, with tropical storm-force winds {{convert|2170|km|mi}} in diameter. The smallest storm on record, [[Cyclone Tracy]], was roughly {{convert|100|km|mi}} wide before striking [[Darwin, Northern Territory|Darwin]], [[Australia]] in 1974.<ref name = "AOML FAQ E5">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: Which are the largest and smallest tropical cyclones on record?|publisher = [[NOAA]] | accessdate= 2006-07-25 | url = http://www.aoml.noaa.gov/hrd/tcfaq/E5.html}}</ref>

[[Hurricane John (1994)|Hurricane John]] is the longest-lasting tropical cyclone on record, lasting 31&nbsp;days in [[1994 Pacific hurricane season|1994]]. Before the advent of satellite imagery in 1961, however, many tropical cyclones were underestimated in their durations.<ref name="john94">{{cite web|author=Neal Dorst|year=2006|title=Which tropical cyclone lasted the longest?|publisher=Hurricane Research Division|accessdate=2007-02-23|url=http://www.aoml.noaa.gov/hrd/tcfaq/E6.html}}</ref> John is the second longest-tracked tropical cyclone in the Northern Hemisphere on record, behind [[1960 Pacific typhoon season#Typhoon Ophelia|Typhoon Ophelia]] of 1960, which had a path of 8,500&nbsp;miles (12,500&nbsp;km). Reliable data for Southern Hemisphere cyclones is unavailable.<ref name="faqe7">{{cite web|author=Neal Dorst|year=2006|url=http://www.aoml.noaa.gov/hrd/tcfaq/E7.html|accessdate=2007-02-23|title=What is the farthest a tropical cyclone has traveled ?|publisher=Hurricane Research Division}}</ref>

==Long-term activity trends==
{{Double image stack|right|NOAA ACE index 1950-2004 RGB.svg|Amo timeseries 1856-present.svg|250|Atlantic Multidecadal Cycle since 1950, using accumulated cyclone energy (ACE)|Atlantic Multidecadal Oscillation Timeseries, 1856–2008}}
:{{seealso|Atlantic hurricane reanalysis}}
While the number of storms in the Atlantic has increased since 1995, there is no obvious global trend; the annual number of tropical cyclones worldwide remains about 87&nbsp;±&nbsp;10. However, the ability of climatologists to make long-term data analysis in certain basins is limited by the lack of reliable historical data in some basins, primarily in the Southern Hemisphere.<ref name="Landsea Trends">{{cite journal | author = [[Chris Landsea|Landsea, Chris]], et al. | title = Can We Detect Trends in Extreme Tropical Cyclones? | url = http://www.aoml.noaa.gov/hrd/Landsea/landseaetal-science06.pdf | journal = [[Science (journal)|Science]] | format = PDF| volume = 313 | pages = 452&ndash;454 | date = [[July 28]], [[2006]] | accessdate = 2007-06-09 | doi = 10.1126/science.1128448 | pmid = 16873634}}</ref> In spite of that, there is some evidence that the intensity of hurricanes is increasing. [[Kerry Emanuel]] stated, "Records of hurricane activity worldwide show an upswing of both the maximum wind speed in and the duration of hurricanes. The energy released by the average hurricane (again considering all hurricanes worldwide) seems to have increased by around 70% in the past 30&nbsp;years or so, corresponding to about a 15% increase in the maximum wind speed and a 60% increase in storm lifetime."<ref name="EmanuelHomepage">{{cite web | url = http://wind.mit.edu/~emanuel/anthro2.htm | author = [[Kerry Emanuel|Emanuel, Kerry]] | title = Anthropogenic Effects on Tropical Cyclone Activity | accessdate = 2006-03-30 | date = January 2006}}</ref>

Atlantic storms are becoming more destructive financially, since five of the ten [[List of Atlantic hurricanes#Listed by cost (United States only)|most expensive storms in United States history]] have occurred since 1990. According to the [[World Meteorological Organization]], “recent increase in societal impact from tropical cyclones has largely been caused by rising concentrations of population and infrastructure in coastal regions.”<ref name="WMO-IWTC">{{cite press release |title=Summary Statement on Tropical Cyclones and Climate Change |publisher=World Meteorological Organization |date=2006-12-04 |url=http://www.wmo.int/pages/prog/arep/press_releases/2006/pdf/iwtc_summary.pdf |format=PDF |language= |accessdate= |quote= }}</ref> Pielke ''et al.'' (2008) normalized mainland U.S. hurricane damage from 1900–2005 to 2005 values and found no remaining trend of increasing absolute damage. The 1970s and 1980s were notable because of the extremely low amounts of damage compared to other decades. The decade 1996–2005 was the second most damaging among the past 11 decades, with only the decade 1926–1935 surpassing its costs. The most damaging single storm is the [[1926 Miami hurricane]], with $157&nbsp;billion of normalized damage.<ref name="Pielke2008">{{ cite journal | last = Pielke | first = Roger A., Jr. | authorlink = | coauthors = ''et al.'' | year = 2008 | month = | title = Normalized Hurricane Damage in the United States: 1900–2005 | journal = Natural Hazards Review | volume = 9 | issue = 1 | pages = 29&ndash;42 | doi = 10.1061/(ASCE)1527-6988(2008)9:1(29) | url = http://forecast.mssl.ucl.ac.uk/shadow/docs/Pielkeetal2006a.pdf | accessdate = | quote = }}</ref>

Often in part because of the threat of hurricanes, many coastal regions had sparse population between major ports until the advent of automobile tourism; therefore, the most severe portions of hurricanes striking the coast may have gone unmeasured in some instances. The combined effects of ship destruction and remote landfall severely limit the number of intense hurricanes in the official record before the era of hurricane reconnaissance aircraft and satellite meteorology. Although the record shows a distinct increase in the number and strength of intense hurricanes, therefore, experts regard the early data as suspect.<ref name="BOM TC Guide 1.3">{{cite web | publisher = [[Bureau of Meteorology]] | url = http://www.bom.gov.au/bmrc/pubs/tcguide/ch1/ch1_3.htm | title = 1.3: A Global Climatology | author = Neumann, Charles J. | work = Global Guide to Tropical Cyclone Forecasting | accessdate = 2006-11-30}}</ref>

The number and strength of Atlantic hurricanes may undergo a 50&ndash;70 year cycle, also known as the [[Atlantic Multidecadal Oscillation]]. Nyberg ''et al.'' reconstructed Atlantic major hurricane activity back to the early 18th century and found five periods averaging 3&ndash;5 major hurricanes per year and lasting 40&ndash;60 years, and six other averaging 1.5&ndash;2.5 major hurricanes per year and lasting 10&ndash;20years. These periods are associated with the Atlantic multidecadal oscillation. Throughout, a decadal oscillation related to solar irradiance was responsible for enhancing/dampening the number of major hurricanes by 1&ndash;2 per year.<ref name="Nyberg2005">{{cite journal |last=Nyberg |first=J. |authorlink= |coauthors=Winter, A.; Malmgren, B. A. |year=2005 |month= |title=Reconstruction of Major Hurricane Activity |journal=Eos Trans. AGU |volume=86 |issue=52, Fall Meet. Suppl. |pages=Abstract PP21C-1597 |id= |url=http://www.agu.org/cgi-bin/wais?dd=PP21C-1597 |accessdate= |quote= }}</ref>

Although more common since 1995, few above-normal hurricane seasons occurred during 1970&ndash;94.<ref name="RMS activity">{{cite web | author = [[Risk Management Solutions]] | url = http://www.rms.com/Publications/60HUActivityRates_whitepaper.pdf | format = PDF | title = U.S. and Caribbean Hurricane Activity Rates. | date = March 2006 | accessdate = 2006-11-30}}</ref> Destructive hurricanes struck frequently from 1926&ndash;60, including many major New England hurricanes. Twenty-one Atlantic tropical storms formed in [[1933 Atlantic hurricane season|1933]], a record only recently exceeded in [[2005 Atlantic hurricane season|2005]], which saw 28 storms. Tropical hurricanes occurred infrequently during the seasons of 1900&ndash;25; however, many intense storms formed during 1870&ndash;99. During the [[1887 Atlantic hurricane season|1887 season]], 19 tropical storms formed, of which a record 4 occurred after [[November 1]] and 11 strengthened into hurricanes. Few hurricanes occurred in the 1840s to 1860s; however, many struck in the early 19th century, including an [[1821 Norfolk and Long Island hurricane|1821 storm]] that made a direct hit on [[New York City]]. Some historical weather experts say these storms may have been as high as [[Saffir-Simpson Hurricane Scale|Category 4]] in strength.<ref name="Columbia CCSR">{{cite web | author = Center for Climate Systems Research | title = Hurricanes, Sea Level Rise, and New York City | url = http://www.ccsr.columbia.edu/information/hurricanes/ | publisher = [[Columbia University]] | accessdate = 2006-11-29}}</ref>

These active hurricane seasons predated satellite coverage of the Atlantic basin. Before the satellite era began in 1960, tropical storms or hurricanes went undetected unless a reconnaissance aircraft encountered one, a ship reported a voyage through the storm, or a storm hit land in a populated area.<ref name="BOM TC Guide 1.3"/> The official record, therefore, could miss storms in which no ship experienced gale-force winds, recognized it as a tropical storm (as opposed to a high-latitude extra-tropical cyclone, a tropical wave, or a brief squall), returned to port, and reported the experience.

Proxy records based on [[Paleotempestology|paleotempestological]] research have revealed that major hurricane activity along the [[Gulf of Mexico]] coast varies on timescales of centuries to millennia.<ref name="Liu1999">{{cite conference |first=Kam-biu |last=Liu |authorlink= |coauthors= |title=Millennial-scale variability in catastrophic hurricane landfalls along the Gulf of Mexico coast |conference=23d Conf. on Hurricanes and Tropical Meteorology |pages= |publisher=Amer. Meteor. Soc. |date=1999 |location=Dallas, TX |url= |pages=374–377 |id= }}</ref><ref name="LiuFearn2000">{{cite journal |last=Liu |first=Kam-biu |authorlink= |coauthors=Fearn, Miriam L. |year=2000 |month= |title=Reconstruction of Prehistoric Landfall Frequencies of Catastrophic Hurricanes in Northwestern Florida from Lake Sediment Records |journal=Quaternary Research |volume=54 |issue=2 |pages=238–245 |doi=10.1006/qres.2000.2166 |url= |accessdate= |quote= }}</ref> Few major hurricanes struck the Gulf coast during 3000–1400 BC and again during the most recent millennium. These quiescent intervals were separated by a hyperactive period during 1400 BC and 1000 AD, when the Gulf coast was struck frequently by catastrophic hurricanes and their landfall probabilities increased by 3–5 times. This millennial-scale variability has been attributed to long-term shifts in the position of the [[Azores High]],<ref name="LiuFearn2000" /> which may also be linked to changes in the strength of the [[North Atlantic Oscillation]].<ref>{{cite journal |last=Elsner |first=James B. |authorlink= |coauthors=Liu, Kam-biu; Kocher, Bethany |year=2000 |month= |title=Spatial Variations in Major U.S. Hurricane Activity: Statistics and a Physical Mechanism |journal=Journal of Climate |volume=13 |issue=13 |pages=2293–2305 |doi=10.1175/1520-0442(2000)013<2293:SVIMUS>2.0.CO;2 |url= |accessdate= |quote= }}</ref>

According to the Azores High hypothesis, an anti-phase pattern is expected to exist between the Gulf of Mexico coast and the Atlantic coast. During the quiescent periods, a more northeasterly position of the Azores High would result in more hurricanes being steered towards the Atlantic coast. During the hyperactive period, more hurricanes were steered towards the Gulf coast as the Azores High was shifted to a more southwesterly position near the Caribbean. Such a displacement of the Azores High is consistent with paleoclimatic evidence that shows an abrupt onset of a drier climate in [[Haiti]] around 3200 [[Radiocarbon dating|<sup>14</sup>C]] years BP,<ref name="Higuera-Gundy1999">{{cite journal |last=Higuera-Gundy |first=Antonia |authorlink= |coauthors=''et al.'' |year=1999 |month= |title=A 10,300 <sup>14</sup>C yr Record of Climate and Vegetation Change from Haiti |journal=Quaternary Research |volume=52 |issue=2 |pages=159–170 |doi=10.1006/qres.1999.2062 |url= |accessdate= |quote= }}</ref> and a change towards more humid conditions in the [[Great Plains]] during the late-Holocene as more moisture was pumped up the [[Mississippi Valley]] through the Gulf coast. Preliminary data from the northern Atlantic coast seem to support the Azores High hypothesis. A 3000-year proxy record from a coastal lake in [[Cape Cod]] suggests that hurricane activity increased significantly during the past 500–1000 years, just as the Gulf coast was amid a quiescent period of the last millennium.

==Global warming==
:{{seealso|Effects of global warming}}
The U.S. [[National Oceanic and Atmospheric Administration]] [[Geophysical Fluid Dynamics Laboratory]] performed a simulation to determine if there is a [[statistics|statistical]] [[Periodic trends|trend]] in the frequency or strength of tropical cyclones over time. The simulation concluded "the strongest hurricanes in the present climate may be upstaged by even more intense hurricanes over the next century as the earth's climate is warmed by increasing levels of greenhouse gases in the atmosphere".<ref name="GFDL warming">{{cite web | author = [[Geophysical Fluid Dynamics Laboratory]] | url = http://www.oar.noaa.gov/spotlite/archive/spot_gfdl.html | title = Global Warming and Hurricanes | accessdate = 2006-11-29 | publisher = [[National Oceanic and Atmospheric Administration]]}}</ref>

In an article in ''[[Nature (journal)|Nature]]'', [[Kerry Emanuel]] stated that potential hurricane destructiveness, a measure combining hurricane strength, duration, and frequency, "is highly correlated with tropical sea surface temperature, reflecting well-documented climate signals, including multidecadal oscillations in the North Atlantic and North Pacific, and global warming". Emanuel predicted "a substantial increase in hurricane-related losses in the twenty-first century".<ref name="Nature Emanuel 2005">{{cite journal | url = ftp://texmex.mit.edu/pub/emanuel/PAPERS/NATURE03906.pdf | format = PDF | author = [[Kerry Emanuel|Emanuel, Kerry]] | journal =[[Nature (journal)|Nature]] | volume = 436 | issue = 7051 | pages = 686–688 | accessdate = 2006-03-20 | title = Increasing destructiveness of tropical cyclones over the past 30 years | doi = 10.1038/nature03906 | year = 2005}}</ref> Similarly, P.J. Webster and others published an article in ''[[Science (journal)|Science]]'' examining the "changes in tropical cyclone number, duration, and intensity" over the past 35&nbsp;years, the period when satellite data has been available. Their main finding was although the number of cyclones decreased throughout the planet excluding the north [[Atlantic Ocean]], there was a great increase in the number and proportion of very strong cyclones.<ref name="Webster et al. 2005">{{cite journal | author = Webster, P. J., G. J. Holland, J. A. Curry and H.-R. Chang | url = http://www.sciencemag.org/cgi/reprint/309/5742/1844.pdf | title = Changes in Tropical Cyclone Number, Duration, and Intensity in a Warming Environment | format = PDF | journal = [[Science (journal)|Science]] | date = [[September 16]], [[2005]] | volume = 309 | issue = 5742 | pages = 1844&ndash;1846 | accessdate = 2006-03-20 | doi = 10.1126/science.1116448 | pmid = 16166514}}</ref>

{{Costliest U.S. Atlantic hurricanes by wealth normalization}}
The strength of the reported effect is surprising in light of modeling studies<ref>{{cite journal|author = Knutson, Thomas R. and Robert E. Tuleya|title= Impact of CO2-Induced Warming on Simulated Hurricane Intensity and Precipitation:Sensitivity to the Choice of Climate Model and Convective Parameterization|journal=Journal of Climate|volume=17|issue=18|year=2004|pages=3477&ndash;3494|doi= 10.1175/1520-0442(2004)017<3477:IOCWOS>2.0.CO;2|doilabel= 10.1175/1520-0442(2004)017&#60;3477:IOCWOS&#62;2.0.CO;2}}</ref> that predict only a one half category increase in storm intensity as a result of a ~2&nbsp;°C (3.6&nbsp;°F) global warming. Such a response would have predicted only a ~10% increase in Emanuel's potential destructiveness index during the 20th century rather than the ~75&ndash;120% increase he reported.<ref name="Nature Emanuel 2005"/> Secondly, after adjusting for changes in population and inflation, and despite a more than 100% increase in Emanuel's potential destructiveness index, no statistically significant increase in the monetary damages resulting from Atlantic hurricanes has been found.<ref>{{cite journal|author=Pielke, R. A. Jr|journal=Nature|doi=10.1038/nature04426|year=2005|title=Meteorology: Are there trends in hurricane destruction?|pages=E11|volume=438}}</ref><ref name="Pielke2008" />

Sufficiently warm [[sea surface temperatures]] are considered vital to the development of tropical cyclones.<ref name = "AOML FAQ A15">{{ cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: How do tropical cyclones form? | publisher = [[NOAA]] | accessdate = 2006-07-26 | url = http://www.aoml.noaa.gov/hrd/tcfaq/A15.html}}</ref> Although neither study can directly link hurricanes with global warming, the increase in sea surface temperatures is believed to be due to both global warming and nature variability, e.g. the hypothesized [[Atlantic Multidecadal Oscillation]] (AMO), although an exact attribution has not been defined.<ref name=realclimate/> However, recent temperatures are the warmest ever observed for many ocean basins.<ref name="Nature Emanuel 2005"/>

In February 2007, the [[United Nations]] [[Intergovernmental Panel on Climate Change]] released its [[IPCC Fourth Assessment Report|fourth assessment report]] on [[climate change]]. The report noted many observed changes in the climate, including atmospheric composition, global average temperatures, ocean conditions, among others. The report concluded the observed increase in tropical cyclone intensity is larger than climate models predict. Additionally, the report considered that it is likely that storm intensity will continue to increase through the 21st century, and declared it more likely than not that there has been some human contribution to the increases in tropical cyclone intensity.<ref name="ipcc">{{cite web|author=Richard Alley, et. al|year=2007|title=Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change|publisher=United Nations|accessdate=2007-02-23|url=http://www.ipcc.ch/ipccreports/ar4-syr.htm|format=HTML}}</ref> However, there is no universal agreement about the magnitude of the effects anthropogenic global warming has on tropical cyclone formation, track, and intensity. For example, critics such as [[Chris Landsea]] assert that man-made effects would be "quite tiny compared to the observed large natural hurricane variability".<ref name = "AOML FAQ G3">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: What may happen with tropical cyclone activity due to global warming? | publisher = [[NOAA]] | accessdate = 2007-06-02 | url = http://www.aoml.noaa.gov/hrd/tcfaq/G3.html}}</ref> A statement by the [[American Meteorological Society]] on [[February 1]], [[2007]] stated that trends in tropical cyclone records offer "evidence both for and against the existence of a detectable anthropogenic signal" in [[tropical cyclogenesis]].<ref name="AMS climate change">{{cite journal | title= Climate Change: An Information Statement of the American Meteorological Society | author = [[American Meteorological Society]] | date = 2007-02-01 | journal = Bulletin of the American Meteorological Society | pages = 5 | url = http://www.ametsoc.org/POLICY/2007climatechange.pdf | format = PDF | volume = 88 | accessdate = 2007-06-03}}</ref> Although many aspects of a link between tropical cyclones and global warming are still being "hotly debated",<ref name="IWTC-VI"/> a point of agreement is that no individual tropical cyclone or season can be attributed to global warming.<ref name="IWTC-VI">{{cite web|author = [[World Meteorological Organization]] | title = Statement on Tropical Cyclones and Climate Change | pages = 6 | url = http://www.wmo.ch/pages/themes/wmoprod/documents/iwtc_statement.pdf | format = PDF | date = [[December 11]], [[2006]] | accessdate = 2007-06-02}}</ref><ref name="realclimate">{{cite web | author = [[Stefan Rahmstorf]], [[Michael E. Mann]], Rasmus Benestad, [[Gavin Schmidt]] and [[William Connolley]] | url = http://www.realclimate.org/index.php?p=181 | title = Hurricanes and Global Warming - Is There a Connection? | publisher = [[RealClimate]] | date = [[September 2]], [[2005]] | accessdate = 2006-03-20}}</ref> Research reported in the [[September 3]], [[2008]] issue of Nature found that the strongest tropical cyclones are getting stronger, particularly over the North Atlantic and Indian oceans. Wind speeds for the strongest tropical storms increased from an average of 140 mph in 1981 to 156 mph in 2006, while the ocean temperature, averaged globally over the all regions where tropical cyclones form, increased from 28.2 degrees Celsius to 28.5 degrees Celsius during this period.<ref>[http://www.nature.com/news/2008/080903/full/news.2008.1079.html Hurricanes are getting fiercer] Nature, Retrieved on [[September 4]], [[2008]].</ref><ref>[http://newswise.com/articles/view/543977/ Warmer Seas Linked to Strengthening Hurricanes: Study Fuels Global Warming Debate] Newswise, Retrieved on [[September 4]], [[2008]].</ref>

==Related cyclone types==
[[Image:Gustav 09 sep 2002 1805Z.jpg|thumb|250px|right|[[Hurricane Gustav (2002)|Subtropical Storm Gustav]] in [[2002 Atlantic hurricane season|2002]]]]
{{seealso|Cyclone|Extratropical cyclone|Subtropical cyclone}}
In addition to tropical cyclones, there are two other classes of cyclones within the spectrum of cyclone types. These kinds of cyclones, known as [[extratropical cyclone]]s and [[subtropical cyclone]]s, can be stages a tropical cyclone passes through during its [[tropical cyclogenesis|formation]] or dissipation.<ref>Mark A. Lander, N. Davidson, H. Rosendal, J. Knaff, and R. Edson, J. Evans, R. Hart. [http://www.aoml.noaa.gov/hrd/iwtc/Lander4-1.html Fifth International Workshop on Tropical Cyclones.] Retrieved on [[2006-12-14]].</ref>

An ''extratropical cyclone'' is a storm that derives energy from horizontal temperature differences, which are typical in higher latitudes. A tropical cyclone can become extratropical as it moves toward higher latitudes if its energy source changes from heat released by condensation to differences in temperature between air masses;<ref name = "AOML FAQ A7">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: What is an extra-tropical cyclone?|publisher = [[NOAA]] | accessdate = 2006-07-25 | url = http://www.aoml.noaa.gov/hrd/tcfaq/A7.html}}</ref> additionally, although not as frequently, an extratropical cyclone can transform into a subtropical storm, and from there into a tropical cyclone. From space, extratropical storms have a characteristic "[[comma (punctuation)|comma]]-shaped" cloud pattern.<ref>[[University of Wisconsin-Madison]]. [http://profhorn.meteor.wisc.edu/wxwise/satmet/lesson14/Satextracyclone.html Lesson 14: Background: Synoptic Scale.] Retrieved on [[2008-02-25]].</ref> Extratropical cyclones can also be dangerous when their low-pressure centers cause powerful winds and high seas.<ref>[[United States Geological Survey]]. [http://pubs.usgs.gov/of/2003/of03-337/winter.html An Overview of Coastal Land Loss: With Emphasis on the Southeastern United States.] Retrieved on [[2008-02-25]].</ref>

A ''subtropical cyclone'' is a [[weather]] system that has some characteristics of a tropical cyclone and some characteristics of an extratropical cyclone. They can form in a wide band of [[latitude]]s, from the [[equator]] to 50°. Although subtropical storms rarely have hurricane-force winds, they may become tropical in nature as their cores warm.<ref name = "AOML FAQ A6">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: What is a sub-tropical cyclone?|publisher = [[NOAA]] | accessdate = 2006-07-25 | url = http://www.aoml.noaa.gov/hrd/tcfaq/A6.html}}</ref> From an operational standpoint, a tropical cyclone is usually not considered to become subtropical during its extratropical transition.<ref name=PadgetDecember2000>{{cite web | author = Padgett, Gary | url = http://australiasevereweather.com/cyclones/2001/summ0012.htm | title = Monthly Global Tropical Cyclone Summary for December 2000 | year = 2001 | accessdate = 2006-03-31}}</ref>

==Tropical cyclones in popular culture==
{{main|Tropical cyclones in popular culture}}
In [[popular culture]], tropical cyclones have made appearances in different types of media, including [[film]]s, [[book]]s, [[television]], [[music]], and [[electronic game]]s. The media can have tropical cyclones that are entirely [[fiction]]al, or can be based on real events.<ref name = "AOML FAQ J4">{{cite web | author = [[Atlantic Oceanographic and Meteorological Laboratory]], Hurricane Research Division | title = Frequently Asked Questions: What fictional books, plays, and movies have been written involving tropical cyclones? | publisher = [[NOAA]] | accessdate = 2006-07-25 | url = http://www.aoml.noaa.gov/hrd/tcfaq/J4.html}}</ref> For example, [[George Rippey Stewart]]'s ''[[Storm (novel)|Storm]]'', a [[best-seller]] published in 1941, is thought to have influenced meteorologists into giving female names to Pacific tropical cyclones.<ref>{{cite web | author = Heidorn, Keith C. | url = http://www.islandnet.com/~see/weather/arts/storm.htm | title = George Stewart's Storm: Remembering A Classic. | accessdate = 2006-12-10 | publisher = The Weather Doctor}}</ref> Another example is the hurricane in ''[[The Perfect Storm (film)|The Perfect Storm]]'', which describes the sinking of the ''[[Andrea Gail]]'' by the [[1991 Halloween Nor'easter]].<ref name="1991 Perfect Storm">{{cite web | author = McCown, Sean | title = Unnamed Hurricane 1991 | work = Satellite Events Art Gallery: Hurricanes | url = http://www.ncdc.noaa.gov/oa/satellite/satelliteseye/hurricanes/unnamed91/unnamed91.html | publisher = [[National Climatic Data Center]] | date = [[December 13]], [[2004]] | accessdate = 2007-02-04}}</ref> Also, [[Tropical cyclones in popular culture|hypothetical hurricanes]] have been featured in parts of the plots of series such as ''[[The Simpsons]]'',<ref name="simpsons">{{cite web| url=http://tv.yahoo.com/the-simpsons/show/hurricane-neddy/episode/618;_ylt=AnBO0HmTjXrsNu0z_MuBbO2zo9EF| title=Hurricane Neddy - Episode Overview| publisher= Yahoo! TV| accessdate=2008-02-26}}</ref> ''[[Invasion (TV series)|Invasion]]'',<ref name="noaafaq">[http://www.aoml.noaa.gov/hrd/tcfaq/J4.html NOAA FAQ: What fictional books, plays, and movies have been written involving tropical cyclones?]</ref> ''[[Family Guy]]'', <ref name="familyguy">{{cite web| url=http://www.starpulse.com/movie/Family_Guy%3A_One_if_By_Clam%2C_Two_if_By_Sea/V299545/0/2/| title="Family Guy: One if by Clam, Two if by Sea - Summary| publisher=starpulse.com| accessdate=2008-02-26}}</ref> ''[[Seinfeld]]'',<ref name="seinfeld">{{cite web | author = TheNewsGuy(Mike) | title = The Checks (Seinfeld Episode Script) | url = http://www.seinfeldscripts.com/TheChecks.html | publisher = Seinfeldscripts.com| accessdate = 2007-02-25}}</ref> ''[[CSI Miami]]'',<ref name="CSIMiami">{{cite web| url=http://www.tvguide.com/detail/tv-show.aspx?episodeid=3962744&tvobjectid=100101&more=ucepisodelist| title=CSI: Miami Episodes - Episode Detail: Hurricane Anthony| publisher=TV Guide| accessdate=2008-02-25}}</ref> and ''[[Dawson's Creek]]''.<ref name="dawsons">{{cite web|url=http://tv.yahoo.com/dawsons-creek/show/episode/34568/recap&vers=long&start=1| title=Dawson's Creek - Hurricane| publisher="Yahoo! TV| accessdate=2008-02-25}}</ref> The 2004 film ''[[The Day After Tomorrow]]'' includes several mentions of actual tropical cyclones as well as featuring fantastical "hurricane-like" non-tropical Arctic storms.<ref>{{cite web|url=http://www.tribute.ca/movies/The+Day+After+Tomorrow/6798| title=The Day After Tomorrow Movie Synopsis| publisher=Tribute.ca| accessdate=2008-02-26}}</ref><ref>{{cite web|url=http://movies.nytimes.com/movie/281154/The-Day-After-Tomorrow/trailers| title=The Day After Tomorrow (2004)| publisher=The New York Times| accessdate=2008-02-26}}</ref>

==See also==
{{tcportal}}
* [[Hypercane]]
* [[List of wettest tropical cyclones by country]]
* [[Secondary flow#Tropical cyclones|Secondary flow in tropical cyclones]]

{{col-begin}}
{{col-2}}

;Annual seasons
* [[List of Atlantic hurricane seasons]] ([[{{CURRENTYEAR}} Atlantic hurricane season|current]])
* [[List of North Indian Ocean cyclone seasons]] ([[{{CURRENTYEAR}} North Indian Ocean cyclone season|current]])
* [[List of Pacific hurricane seasons]] ([[{{CURRENTYEAR}} Pacific hurricane season|current]])
* [[List of Pacific typhoon seasons]] ([[{{CURRENTYEAR}} Pacific typhoon season|current]])
* [[List of Southern Hemisphere cyclone seasons]] ([[{{#ifexpr:{{#time:n}}>6|{{#time:Y}}-{{#time:y|+1 year}}|{{#time:Y|-1 year}}-{{#time:y}}}} Southern Hemisphere tropical cyclone season|current]])
{{col-2}}

;Forecasting and preparation
* [[Catastrophe modeling]]
* [[Hurricane Engineering]]
* [[Hurricane preparedness]]
* [[Hurricane proof building]]
* [[Tropical cyclone watches and warnings]]
{{col-end}}
{{Cyclones}}

==References==
{{reflist|2}}

==External links==
{{wiktionary}}
{{commonscat|Tropical cyclones}}

;Learning resources
* [http://www.ahtfund.org/ Anti hurricane technology]
* [http://www.ncdc.noaa.gov/oa/esb/?goal=weather&file=events/hurricane/ Economic Costs of Hurricanes and associated Economic Benefits from Improved Forecasting]
* [http://www.fema.gov/kids/hurr.htm FEMA for Kids: Hurricanes]
* {{PDF|[http://www.nhc.noaa.gov/marinersguide.pdf Mariner's Guide for Hurricane Awareness]|1.23&nbsp;[[Mebibyte|MiB]]<!-- application/pdf, 1290745 bytes -->}}
* [http://www.researchchannel.org/prog/displayevent.aspx?rID=19645&fID=345 Is Global Climate Change Affecting Hurricanes?]
* [http://www.pbs.org/wgbh/nova/teachers/viewing/3204_02_nsn.html NOVA science now: Hurricanes]
* [http://www.edu4hazards.org/hurricane.html Surviving a hurricane – A guide for children and youth]
* [http://www.aoml.noaa.gov/hrd/tcfaq/A1.html Summary of cyclone terminology from NOAA FAQ]
* [http://www.solar.ifa.hawaii.edu/Tropical/tropical.html Tropical Storms Worldwide] – by Hawaii University
* [http://www.bom.gov.au/bmrc/pubs/tcguide/ch1/ch1_3.htm WMO guide on cyclone terminology]
* [http://severe.worldweather.org/ World Meteorological Organization Severe Weather Information Center] – Shows all current tropical systems worldwide and their tracks
;Regional specialised meteorological centers
* [http://www.atl.ec.gc.ca/weather/hurricane/index_e.html Canadian Hurricane Centre] - Canadian Maritimes
* [http://www.cdera.org/ Caribbean Disaster Emergency Response Agency] - Caribbean region
* [http://www.stormcarib.com/ Caribbean Hurricane Network] - Caribbean region
* [http://www.prh.noaa.gov/hnl/cphc/ Central Pacific Hurricane Center] – Central Pacific
* [http://www.met.gov.fj/index.php?id=152 Fiji Meteorological Service] – South Pacific east of 160°, north of 25° S
* [http://www.imd.gov.in/ India Meteorological Department] – [[Bay of Bengal]] and the [[Arabian Sea]]
* [http://www.jma.go.jp/en/typh/ Japan Meteorological Agency] – NW Pacific
* [http://www.meteo.fr/temps/domtom/La_Reunion/ Météo-France – La Reunion] – South Indian Ocean from Africa to 90° E
* [http://www.nhc.noaa.gov/ US National Hurricane Center] – North Atlantic, Eastern Pacific

;Past storms
* [http://agora.ex.nii.ac.jp/digital-typhoon/ Digital Typhoon: Typhoon Images and Information]
* [http://www.bom.gov.au/bmrc/pubs/tcguide/ch1/ch1_3.htm Global climatology of tropical cyclones]
* [http://www.ncdc.noaa.gov/oa/rsad/gibbs/gibbs.html Global ISCCP B1 Browse System Satellite Archive]
* [http://weather.unisys.com/hurricane/ Unisys historical and contemporary hurricane track data]
* [http://www.hpc.ncep.noaa.gov/tropical/rain/tcrainfall.html United States Tropical Cyclone Rainfall Climatology] – Nearly 30&nbsp;years of tropical cyclone histories with an emphasis on storm total rainfall, in color, up to present. Broken up by year, region, by point of landfall, and North American countries impacted
* [http://www.stormpulse.com Interactive hurricane tracking map] - Includes hurricane data all the way back to the 1850s

{{featured article}}

[[Category:Basic meteorological concepts and phenomena]]
[[Category:Tropical cyclone meteorology| ]]
[[Category:Tropical cyclones| ]]
[[Category:Types of cyclone]]
[[Category:Vortices]]
[[Category:Weather hazards]]

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Revision as of 04:00, 9 September 2008

Hurricanes are fucking COOL.

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