Tropical cyclones, also known as hurricanes or typhoons, are large storm systems that form over warm tropical oceans and are characterized by strong winds that spiral inward toward the eye of the storm. They develop when warm, moist air rises and condenses, releasing latent heat that powers the storm. Tropical cyclones strengthen over warm ocean waters due to evaporation that fuels thunderstorms and heavy rain. They weaken rapidly when moving over land away from their heat source. Major tropical cyclone basins are monitored by regional warning centers that track storms and issue advisories.

1. Tropical cyclone
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A tropical cyclone is a storm systemcharacterized by a large low-pressure center and
numerous thunderstorms that produce strong winds and heavy rain. Tropicalcyclones strengthen when water
evaporated from the ocean is released as the saturatedair rises, resulting in condensation of water
vapor contained in the moist air. They are fueled by a different heat mechanism than other cyclonic windstorms
such asnor'easters, European windstorms, and polar lows. The characteristic that separates tropical cyclones
from other cyclonic systems is that at any height in the atmosphere, the center of a tropical cyclone will be
warmer than its surroundings; a phenomenon called "warm core" storm systems.
The term "tropical" refers both to the geographical origin of these systems, which usually form
in tropical regions of the globe, and to their formation in maritime tropical air masses. The term "cyclone" refers
to such storms' cyclonic nature, with counterclockwise wind flow in the Northern Hemisphere and clockwise
wind flow in theSouthern Hemisphere. The opposite direction of the wind flow is a result of the Coriolis force.
Depending on its location and strength, a tropical cyclone is referred to by names such
as hurricane (/ˈhʌrɨkeɪn/, /ˈhʌrɨkən/), 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 as well as spawning tornadoes. They develop over large bodies of
warm water, and lose their strength if they move over land due to increased surface friction and loss of the
warm ocean as an energy source. This is why coastal regions can receive significant damage from a tropical
cyclone, while inland regions are relatively safe from receiving strong winds. Heavy rains, however, can

3. produce significant flooding inland, and storm surges can produce extensive coastal flooding up to 40
kilometres (25 mi) from the coastline. Although their effects on human populations can be devastating, tropical
cyclones can relieve drought conditions. They also carry heat 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 develop when the atmospheric conditions around a weak disturbance in the
atmosphere are favorable. The background environment is modulated by climatological cycles and patterns
such as the Madden-Julian oscillation, El Niño-Southern Oscillation, and the Atlantic multidecadal oscillation.
Others form when other types of cyclones acquire tropical characteristics. Tropical systems are then moved
by steering winds in the troposphere; if the conditions remain favorable, the tropical disturbance intensifies, and
can even develop an 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. It is not possible to
artificially induce the dissipation of these systems with current technology.
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4. Contents
[hide]
1 Physical structure
o 1.1 Eye and center
o 1.2 Size
2 Mechanics
3 Major basins and related warning centers
4 Formation
o 4.1 Times
o 4.2 Factors
o 4.3 Locations
5 Movement and track
o 5.1 Steering winds
o 5.2 Coriolis effect
o 5.3 Interaction with the mid-latitude westerlies
o 5.4 Landfall
o 5.5 Multiple storm interaction
6 Dissipation
o 6.1 Factors
o 6.2 Artificial dissipation
7 Effects
8 Observation and forecasting
o 8.1 Observation
o 8.2 Forecasting
9 Classifications, terminology, and naming
o 9.1 Intensity classifications
 9.1.1 Tropical depression
 9.1.2 Tropical storm
 9.1.3 Hurricane or typhoon
o 9.2 Origin of storm terms
o 9.3 Naming
10 Notable tropical cyclones

5. 11 Changes caused by El Niño-Southern Oscillation
12 Long-term activity trends
13 Global warming
14 Related cyclone types
15 Tropical cyclones in popular culture
16 See also
17 References
18 External links
[edit]Physical structure
See also: Eye (cyclone)
All tropical cyclones are areas of low atmospheric pressure in the Earth's atmosphere. The pressures recorded
at the centers of tropical cyclones are among the lowest that occur on Earth's surface at sea level.[1] 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.[2]
[edit]Eye and center
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 a large "eye". Weather in the eye is normally calm and free of clouds, although the
sea may be extremely violent.[3] The eye is normally circular in shape, and is typically 30–65 km (19–40 miles)
in diameter, though eyes as small as 3 kilometres (1.9 mi) and as large as 370 kilometres (230 mi) have been
observed.[4][5] Intense, mature tropical cyclones can sometimes exhibit an outward curving of the eyewall's top,
making it resemble an arena football stadium; this phenomenon is thus sometimes referred to as the stadium
effect.[6] It is usually coldest in the center.
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; [7] in weaker tropical
cyclones, the CDO may cover the center completely.[8] 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.[3] Eyewall replacement cycles occur naturally in intense tropical cyclones. When cyclones reach peak
intensity they usually have an eyewall and radius of maximum winds that contract to a very small size, around

6. 10 to 25 kilometres (6.2 to 16 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.[9]
Size descriptions of tropical cyclones
ROCI Type
Less than 2 degrees latitude Very small/midget
2 to 3 degrees of latitude Small
3 to 6 degrees of latitude Medium/Average
6 to 8 degrees of latitude Large
Over 8 degrees of latitude Very large[10]
[edit]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 isobar, also known as its ROCI. If the radius is less than twodegrees of
latitude or 222 kilometres (138 mi), then the cyclone is "very small" or a "midget". A radius between 3 and
6 latitude degrees or 333 to 670 kilometres (207 to 420 mi) are considered "average-sized". "Very large"
tropical cyclones have a radius of greater than 8 degrees or 888 kilometres (552 mi).[10] 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 cyclones roughly half their size.[11] 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 vorticityfield decreases to 1×10−5 s−1 from its center.[12][13]
[edit]Mechanics

7. Tropical cyclones form when the energy released by the condensation of moisture in rising air causes a positive feedback
loop over warm ocean waters.[14]
A tropical cyclone's primary energy source is the release of the heat of condensation from water
vaporcondensing, 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
therotation and gravity of the Earth.[15] In another way, tropical cyclones could be viewed as a special type
ofmesoscale convective complex, which continues to develop over a vast source of relative warmth and
moisture. While an initial warm core system, such as an organized thunderstorm complex, is necessary for the
formation of a tropical cyclone, a large flux of energy is needed to lower atmospheric pressuremore than a few
millibars (0.10 inch of mercury). The inflow of warmth and moisture from the underlying ocean surface is critical
for tropical cyclone strengthening.[16] A significant amount of the inflow in the cyclone is in the lowest 1
kilometre (3,300 ft) of the atmosphere.[17]
Condensation leads to higher wind speeds, as a tiny fraction of the released energy is converted into
mechanical energy;[18] 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 drivesupdrafts that
increase the height of the storm clouds, speeding up condensation.[19] This positive feedback loop, called
the Wind-induced surface heat exchange, continues for as long as conditions are favorable for 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, giving it a cyclonic characteristic and affecting the trajectory of the storm.[20][21][22] In
the Northern Hemisphere, where the cyclone's wind flow is counterclockwise, the fastest winds relative to the
surface of the Earth occur on the eastern side of a northward-moving storm and on the northern side of a
westward-moving one; the opposite occurs in the Southern Hemisphere, where the wind flow is clockwise.[23]
What primarily distinguishes tropical cyclones from other meteorological phenomena is deep convection as a
driving force.[24] Because convection is strongest in a tropical climate, it defines the initial domain of the tropical
cyclone. By contrast, mid-latitude cyclones draw their energy mostly from pre-existing horizontal
temperature gradients in the atmosphere.[24] To continue to drive its heat engine, a tropical cyclone must
remain over warm water, which provides the needed atmospheric moisture to keep the positive feedback loop

8. running. When a tropical cyclone passes over land, it is cut off from its heat source and its strength diminishes
rapidly.[25]
Chart displaying the drop in surface temperature in the Gulf of Mexico as HurricanesKatrina and Rita passed over
The passage of a tropical cyclone over the ocean causes the upper layers of the ocean to cool substantially,
which can influence subsequent cyclone development. This cooling is primarily caused by wind-driven mixing
of cold water from deeper in the ocean and the warm surface waters. This effect results in a negative feedback
process that can inhibit further development or lead to weakening. Additional cooling may come in the form of
cold water from falling raindrops (this is because the atmosphere is cooler at higher altitudes). 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.[26]
Scientists estimate that a tropical cyclone releases heat energy at the rate of 50 to 200 exajoules(1018 J) per
day,[19] equivalent to about 1 PW (1015 watt). This rate of energy release is equivalent to 70 times the world
energy consumption of humans and 200 times the worldwide electrical generating capacity, or to exploding a
10-megaton nuclear bomb every 20 minutes.[19][27]
In the lower troposphere, the most obvious motion of clouds is toward the center. However 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.[15] This outflow produces
high, cirrus clouds that spiral away from the center. The clouds thin as they move outwards from the center of
the system and are evaporated. They may be thin enough for the sun to be visible through them. These high
cirrus clouds may be the first signs of an approaching tropical cyclone. [28] As air parcels are lifted within the eye
of the storm the vorticity is reduced, causing the outflow from a tropical cyclone to have anti-cyclonic motion.
[edit]Major basins and related warning centers
Main articles: Tropical cyclone basins and Regional Specialized Meteorological Center

9. Basins and WMO Monitoring Institutions[29]
Basin Responsible RSMCs and TCWCs
North Atlantic National Hurricane Center (United States)
North-East Pacific National Hurricane Center (United States)
North-Central Pacific Central Pacific Hurricane Center (United States)
North-West Pacific Japan Meteorological Agency
North Indian Ocean India Meteorological Department
South-West Indian Ocean Météo-France
Bureau of Meteorology† (Australia)
Australian region Meteorological and Geophysical Agency† (Indonesia)
Papua New Guinea National Weather Service†
Fiji Meteorological Service
Southern Pacific
Meteorological Service of New Zealand†
†
: Indicates a Tropical Cyclone Warning Center
There are six Regional Specialized Meteorological Centers(RSMCs) worldwide. These organizations are
designated by theWorld Meteorological Organization and are responsible for tracking and issuing bulletins,
warnings, and advisories about tropical cyclones in their designated areas of responsibility. In addition, there
are sixTropical Cyclone Warning Centers(TCWCs) that provide information to smaller regions.[30] 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.[31] 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.[32] The Canadian

10. Hurricane Center(CHC) issues advisories on hurricanes and their remnants for Canadian citizens when they
affect Canada.[33]
On 26 March 2004, Cyclone Catarina became the first recorded South Atlantic cyclone and subsequently
struck southern Brazil with winds equivalent to Category 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.[34]
[edit]Formation
Main article: Tropical cyclogenesis
Map of the cumulative tracks of all tropical cyclones during the 1985–2005 time period. ThePacific Ocean west of
the International Date Linesees more tropical cyclones than any other basin, while there is almost no activity in the Atlantic
Ocean south of the Equator.
Map of all tropical cyclone tracks from 1945 to 2006. Equal-area projection.
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 while November is the only
month with all the tropical cyclone basins active.[35]
[edit]Times

11. In the Northern Atlantic Ocean, a distinct cyclone season occurs from June 1 to November 30, sharply peaking
from late August through September.[35] The statistical peak of the Atlantic hurricane season is 10 September.
The Northeast Pacific Ocean has a broader period of activity, but in a similar time frame to the Atlantic.[36] 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.[35] In the Southern Hemisphere, the tropical cyclone year begins on July 1 and runs all
year-round and encompasses the tropical cyclone seasons, which run from November 1 until the end of April,
with peaks in mid-February to early March.[35][37]
Season lengths and seasonal averages[35][38]
Tropical Storms Tropical Cyclones Category 3+ TCs
Basin Season start Season end
(>34 knots) (>63 knots) (>95 knots)
Northwest Pacific April January 26.7 16.9 8.5
South Indian November April 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 November April 9 4.8 1.9
North Indian April December 5.4 2.2 0.4
[edit]Factors

12. 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.[39] While six factors appear to be generally necessary, tropical cyclones may occasionally form
without meeting all of the following conditions. In most situations, water temperatures of at least 26.5
°C (79.7 °F) are needed down to a depth of at least 50 m (160 ft);[40] waters of this temperature cause the
overlying atmosphere to be unstable enough to sustain convection and thunderstorms.[41]Another factor is rapid
cooling with height, which allows the release of the heat of condensation that powers a tropical cyclone.[40] 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.[40] Low amounts of wind shear are
needed, as high shear is disruptive to the storm's circulation.[40] Tropical cyclones generally need to form more
than 555 km (345 mi) or 5 degrees of latitude away from the equator, allowing the Coriolis effect to deflect
winds blowing towards the low pressure center and creating a circulation. [40] Lastly, a formative tropical cyclone
needs a pre-existing system of disturbed weather, although without a circulation no cyclonic development will
take place.[40] Low-latitude and low-level westerly wind bursts associated with theMadden-Julian oscillation can
create favorable conditions for tropical cyclogenesis by initiating tropical disturbances. [42]
[edit]Locations
Most tropical cyclones form in a worldwide band of thunderstorm activity called by several names: the
Intertropical Front (ITF), the Intertropical Convergence Zone (ITCZ), or the monsoon trough.[43][44][45]Another
important source of atmospheric instability is found in tropical waves, which cause about 85% of intense
tropical cyclones in the Atlantic ocean, and become most of the tropical cyclones in the Eastern Pacific
basin.[46][47][48]
Tropical cyclones move westward when equatorward of the subtropical ridge, intensifying as they move. Most
of these systems form between 10 and 30 degrees away of the equator, and 87% form no farther away than
20 degrees of latitude, north or south.[49][50] Because the Coriolis effect initiates and maintains tropical cyclone
rotation, tropical cyclones rarely form or move within about 5 degrees of the equator, where the Coriolis effect
is weakest.[49] However, it is possible for tropical cyclones to form within this boundary as Tropical Storm
Vamei did in 2001 and Cyclone Agni in 2004.[51][52]
[edit]Movement and track
[edit]Steering winds
See also: Prevailing winds

13. Although tropical cyclones are large systems generating enormous energy, their movements over the Earth's
surface are controlled by large-scale winds—the streams in the Earth's atmosphere. The path of motion is
referred to as a tropical cyclone's track and has been compared by Dr. Neil Frank, former director of
the National Hurricane Center, to "leaves carried along by a stream".[53]
Tropical systems, while generally located equatorward 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.[53] In the tropical North Atlantic and Northeast Pacific oceans, trade winds—another name
for the westward-moving wind currents—steer tropical waveswestward from the African coast and towards the
Caribbean Sea, North America, and ultimately into the central Pacific ocean before the waves dampen
out.[47] These waves are the precursors to many tropical cyclones within this region.[46] In the Indian Ocean and
Western Pacific (both north and south of the equator), tropical cyclogenesis is strongly influenced by the
seasonal movement of theIntertropical Convergence Zone and the monsoon trough, rather than by easterly
waves.[54] Tropical cyclones can also be steered by other systems, such as other low pressure systems, high
pressure systems, warm fronts, and cold fronts.
[edit]Coriolis effect
Infrared image of a powerful southern hemisphere 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.[55] 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.[21]

14. 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.[19]
[edit]Interaction with the mid-latitude westerlies
See also: Westerlies
Storm track of Typhoon Ioke, showing recurvature off the Japanese coast in 2006
When a tropical cyclone crosses the subtropical ridgeaxis, 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 begunrecurvature.[56] 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 cyclones 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 Typhoon Ioke in 2006, which took a similar
trajectory.[57]
[edit]Landfall
See also: List of notable tropical cyclones and Unusual areas of tropical cyclone formation
Officially, landfall is when a storm's center (the center of its circulation, not its edge) crosses the
coastline.[58] 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.[58] As a result of the narrowness of 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.[58]
[edit]Multiple storm interaction

15. 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.[59]
[edit]Dissipation
[edit]Factors
Tropical Storm Franklin, an example of a strongly sheared tropical cyclone in the Atlantic Basin during 2005
A tropical cyclone can cease to have tropical characteristics in 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.[60] 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 cyclones. There is a chance a tropical cyclone could regenerate
if it managed to get back over open warm water, such as with Hurricane Ivan. If it remains over mountains for
even a short time, weakening will accelerate.[61] Many storm fatalities occur in mountainous terrain, as the dying
storm unleashes torrential rainfall,[62] leading to deadlyfloods and mudslides, similar to those that happened
with Hurricane Mitch in 1998.[63] In addition, dissipation can occur if a storm remains in the same area of ocean
for too long, mixing the upper 60 metres (197 ft) of water, dropping sea surface temperatures more than 5
°C (9 °F).[64] Without warm surface water, the storm cannot survive.[65]

16. A tropical cyclone can dissipate when it moves over waters significantly below 26.5 °C (79.7 °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.[66] 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.[67] In addition, 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 days.[68] 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 oceanand 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
windstorms; Hurricane Iris's extratropical remnants are an example of such a windstorm from 1995.[69]In
addition, 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. [67] Studies in the 2000s
have given rise to the hypothesis that large amounts of dust reduce the strength of tropical cyclones. [70]
[edit]Artificial dissipation
In the 1960s and 1970s, the United States government attempted to weaken hurricanes throughProject
Stormfury by 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.[71] The winds of Hurricane Debbie—a hurricane seeded in Project Stormfury—dropped as
much as 31%, but Debbie regained its strength after each of two seeding forays.[72] 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.[73] 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 hours, greatly reducing the number of possible test storms. The
project was dropped after it was discovered that 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.[74]
Other approaches have been suggested over time, including cooling the water under a tropical cyclone by
towing icebergs into the tropical oceans.[75] Other ideas range from covering the ocean in a substance that
inhibits evaporation,[76] dropping large quantities of ice into the eye at very early stages of development (so that
the latent heat is absorbed by the ice, instead of being converted to kinetic energy that would feed the positive
feedback loop),[75] or blasting the cyclone apart with nuclear weapons.[18] Project Cirrus even involved throwing

17. dry ice on a cyclone.[77] These approaches all suffer from one flaw above many others: tropical cyclones are
simply too large and short-lived for any of the weakening techniques to be practical.[78]
[edit]Effects
The aftermath of Hurricane Katrina in Gulfport, Mississippi.
Main article: 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.[79] Tropical cyclones stir up water, leaving a cool wake behind them, which
causes the region to be less favorable for subsequent tropical cyclones.[26] On land, strongwinds 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. [80] The broad rotation of a
landfalling tropical cyclone, and vertical wind shear at its periphery, spawns tornadoes. Tornadoes can also be
spawned as a result of eyewall mesovortices, which persist until landfall.[81]
Over the past two centuries, tropical cyclones have been responsible for the deaths of about 1.9 million people
worldwide. Large areas of standing water caused by flooding lead to infection, as well as contributing to
mosquito-borne illnesses. Crowded evacuees in shelters increase the risk of disease propagation.[82] Tropical
cyclones significantly interrupt infrastructure, leading to power outages, bridge destruction, and the hampering
of reconstruction efforts.[82][83]
Although cyclones take an enormous toll in lives and personal property, they may be important factors in
the precipitation regimes of places they impact, as they may bring much-needed precipitation to otherwise dry
regions.[84] Tropical cyclones also help maintain the global heat balance by moving warm, moist tropical air to
the middle latitudes and polar regions,[22] and by regulating thethermohaline
circulation through upwelling.[85] The storm surge and winds of hurricanes may be destructive to human-made
structures, but they also stir up the waters of coastal estuaries, which are typically important fish breeding
locales. Tropical cyclone destruction spurs redevelopment, greatly increasing local property values.[86]

18. [edit]Observation and forecasting
[edit]Observation
Main article: Tropical cyclone observation
Sunset view of Hurricane Isidore's rainbands photographed at 7,000 feet (2,100 m)
Intense tropical cyclones pose a particular observation challenge, as they are a dangerous oceanic
phenomenon, and weather stations, being relatively sparse, are rarely available on the site of the storm itself.
In general, surface observations are available only if the storm is passing over an island or a coastal area, or if
there is a nearby ship. Real-time measurements are usually 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.[87]
Tropical cyclones far from land are tracked by weather satellites capturing 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 Doppler radar. Radar plays a crucial role around landfall by showing a storm's location and intensity
every several minutes.[88]
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 governmenthurricane
hunters.[89] The aircraft used are WC-130 Hercules and WP-3D Orions, both four-engineturboprop cargo
aircraft. These aircraft fly directly into the cyclone and take direct and remote-sensing measurements. The
aircraft also launch GPS dropsondes 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 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.[90]

19. A general decrease in error trends in tropical cyclone path prediction is evident since the 1970s
[edit]Forecasting
See also: Tropical cyclone track forecasting,Tropical cyclone prediction model, and 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 hPa pressure surface (3,000 metres / 9,800
feet 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.[91] High-speed
computers and sophisticated simulation software allow forecasters to produce 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.[92] However, scientists are not as skillful at predicting the intensity of tropical
cyclones.[93]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.
[edit]Classifications, terminology, and naming
[edit]Intensity classifications
Main article: Tropical cyclone scales

20. Three tropical cyclones at different stages of development. The weakest (left) demonstrates only the most basic circular
shape. A stronger storm (top right) demonstrates spiral banding and increased centralization, while the strongest (lower
right) has developed an 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 in the Northwestern Pacific reaches hurricane-strength winds on theBeaufort scale, it is
referred to as a typhoon; if a tropical storm passes the same benchmark in theNortheast Pacific Basin, or in the
Atlantic, it is called a hurricane.[58] Neither "hurricane" nor "typhoon" is used in either the Southern Hemisphere
or the Indian Ocean. In these basins, storms of tropical nature are referred to simply as "cyclones".
As indicated in the table below, each basin uses a separate 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 asHurricane/Typhoon
Ioke in 2006); on rare occasions, the reverse will occur.[94] It should also be noted that typhoons with sustained
winds greater than 67 metres per second (130 kn) or 150 miles per hour (240 km/h) are called Super
Typhoons by the Joint Typhoon Warning Center.[95]
[edit]Tropical depression
A tropical depression is an organized system of clouds and thunderstorms with a defined, closed surface
circulation and maximum sustained winds of less than 17 metres per second (33 kn) or 38 miles per hour
(61 km/h). It has no 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".[15] The practice of

21. the Philippines is to name tropical depressions from their own naming convention when the depressions are
within the Philippines' area of responsibility.[96]
[edit]Tropical storm
A tropical storm is an organized system of strong thunderstorms with a defined surface circulation and
maximum sustained winds between 17 metres per second (33 kn) (39 miles per hour (63 km/h)) and 32 metres
per second (62 kn) (73 miles per hour (117 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).[15]
[edit]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 33 metres per second (64 kn) or 74 miles per hour
(119 km/h).[15] 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 16 kilometres (9.9 mi) to 80
kilometres (50 mi) wide in which the strongest thunderstorms and winds circulate around the storm's center.
Maximum sustained winds in the strongest tropical cyclones have been estimated at about 85 metres per
second (165 kn) or 195 miles per hour (314 km/h).[97]
[hide]Tropical Cyclone Classifications (all winds are 10-minute averages)[98][99]
10-minute
N Indian SW Indian NW NW NE Pacific &
Beaufort sustained Australia SW Pacific
Ocean Ocean Pacific Pacific N Atlantic
scale winds BOM FMS
IMD MF JMA JTWC NHC, CHC& CPHC
(knots)
<28 knots
Trop.
0–6 (32 mph; Depression
Disturbance
52 km/h)
Tropical
Depression
28–29 knots
Tropical Tropical Tropical
(32–33 mph; Tropical Depression
Low Depression Depression
52–54 km/h)
Deep
7 Depression
Depression
30–33 knots
Tropical
(35–38 mph;
Storm
56–61 km/h)

22. 34–47 knots Moderate Tropical
Cyclonic Tropical Tropical
8–9 (39–54 mph; Tropical Cyclone
Storm Cyclone (1) Storm
63–87 km/h) Storm (1)
48–55 knots
(55–63 mph;
10
89–102 Tropical Storm
km/h)
Severe Severe Tropical Severe
Tropical
Cyclonic Tropical Cyclone Tropical
Cyclone (2)
Storm Storm (2) Storm
56–63 knots
(64–72 mph;
11
104–117
km/h)
64–72 knots
(74–83 mph;
Hurricane (1)
119–133
km/h) Severe
Severe
Tropical
Tropical
Cyclone
Cyclone (3)
73–85 knots (3)
(84–98 mph; Tropical
135–157 Cyclone
km/h)
Hurricane (2)
Typhoon
86–89 knots
(99–102
mph; 159–
165 km/h)
Very Severe Severe
Severe
12 Cyclonic Tropical Typhoon
Tropical
Storm Cyclone
90–106 Cyclone (4)
(4)
knots (100–
122 mph;
170–196
km/h)
Intense
Tropical Major Hurricane (3)
Cyclone
107–114
knots (123–
131 mph;
198–211 Severe
km/h) Severe
Tropical
Tropical
Cyclone
Cyclone (5)
(5)
115–119 Super
knots (132– Very Intense Major Hurricane (4)
Typhoon
137 mph; Tropical
213–220

23. km/h) Cyclone
120–135
knots (140–
155 mph;
220–250
km/h) Super
Cyclonic
Storm
>136 knots
(157 mph; Major Hurricane (5)
252 km/h)
[edit]Origin of storm terms
Taipei 101 endures a typhoon in 2005
The word typhoon, which is used today in the Northwest Pacific, may be derived
from Hindi/Urdu,Persian and Arabic ţūfān (‫ ,)طوف ان‬which in turn originates from Greek Typhon (Τυφών), a
monster fromGreek mythology associated with storms.[100] The related Portuguese word tufão, used in
Portuguese for typhoons, is also derived from Typhon.[101] The word is also similar to Chinese "taifeng"
("toifung" inCantonese) (颱風 – great winds), and also to the Japanese "taifu" (台風).
The word hurricane, used in the North Atlantic and Northeast Pacific, is derived from huracán, the Spanish
word for the Carib/Taino storm god, Juracán. This god is believed by scholars to have been at least partially
derived from the Mayan creator god, Huracan. Huracan was believed by the Maya to have created dry land out
of the turbulent waters. The god was also credited with later destroying the "wooden people", the precursors to
the "maize people", with an immense storm and flood.[102][103]Huracan is also the source of the word orcan,
another word for a particularly strong European windstorm.[103]
[edit]Naming
Main articles: Tropical cyclone naming and Lists of tropical cyclone names

24. 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.[104] In most cases, a tropical cyclone retains its name throughout its life; however, under special
circumstances, tropical cyclones may be renamed while active. These names are taken from lists that vary
from region to region and are usually 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.
Different countries have different local conventions; for example, in Japan, storms are referred to by number
(each year), such as 台風第9号 (Typhoon #9).
[edit]Notable tropical cyclones
Main articles: List of notable tropical cyclones, List of Atlantic hurricanes, and 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 people[105] and potentially as many as 1 million[106] after striking the densely
populated Ganges Delta region of Bangladesh on 13 November 1970. Its powerful storm surge was
responsible for the high death toll.[105] The North Indian cyclone basin has historically been the deadliest
basin.[82][107] Elsewhere, Typhoon Nina killed nearly 100,000 in China in 1975 due to a 100-year flood that
caused 62 dams including the Banqiao Dam to fail.[108] The Great Hurricane of 1780 is the deadliest Atlantic
hurricane on record, killing about 22,000 people in theLesser Antilles.[109] 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,[110] while in 1982, the unnamed tropical
depression that eventually became Hurricane Paul killed around 1,000 people in Central America.[111]
Hurricane Katrina is estimated as the costliest tropical cyclone worldwide,[112] causing $81.2 billion in property
damage (2008 USD)[113] with overall damage estimates exceeding $100 billion (2005 USD).[112] Katrina killed at
least 1,836 people after striking Louisiana and Mississippi as amajor hurricane in August 2005.[113] Hurricane
Andrew is the second most destructive tropical cyclone in U.S history, with damages totaling $40.7 billion
(2008 USD), and with damage costs at $31.5 billion (2008 USD), Hurricane Ike is the third most destructive
tropical cyclone in U.S history. The Galveston Hurricane of 1900 is the deadliest natural disaster in the United
States, killing an estimated 6,000 to 12,000 people in Galveston, Texas.[114] Hurricane Mitch caused more than
10,000 fatalities in Latin America. Hurricane Iniki in 1992 was the most powerful storm to strike Hawaii in
recorded history, hitting Kauai as a Category 4 hurricane, killing six people, and causing U.S. $3 billion in
damage.[115]Kauai was also struck by Hurricanes Dot (1959) and Iwa (1982) (see List of Hawaii hurricanes).
Other destructive Eastern Pacific hurricanes include Pauline and Kenna, both causing severe damage after

25. striking Mexico as major hurricanes.[116][117] In March 2004, Cyclone Gafilo struck northeasternMadagascar as a
powerful cyclone, killing 74, affecting more than 200,000, and becoming the worst cyclone to affect the nation
for more than 20 years.[118]
The relative sizes of Typhoon Tip, Cyclone Tracy, and theContiguous 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 mbar (652.5 mmHg) and maximum sustained wind speeds of 165 knots (85 m/s) or
190 miles per hour (310 km/h).[119] Tip, however, does not solely hold the record for fastest sustained winds in a
cyclone. Typhoon Keith in the Pacific and Hurricanes Camille andAllen in the North Atlantic currently share this
record with Tip.[120] Camille was the only storm to actually strike land while at that intensity, making it, with 165
knots (85 m/s) or 190 miles per hour (310 km/h) sustained winds and 183 knots (94 m/s) or 210 miles per hour
(340 km/h) gusts, the strongest tropical cyclone on record at landfall.[121] Typhoon Nancy in 1961 had recorded
wind speeds of 185 knots (95 m/s) or 215 miles per hour (346 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.[97] Likewise, a surface-level gust caused by Typhoon Paka on Guam was
recorded at 205 knots (105 m/s) or 235 miles per hour (378 km/h). Had it been confirmed, it would be the
strongest non-tornadic wind ever recorded on the Earth's surface, but the reading had to be discarded since
theanemometer was damaged by the storm.[122] Hurricane Wilma is the most intense tropical cyclone in the
Atlantic Basin and the strongest tropical cyclone in the Western Hemisphere.
In addition to being the most intense tropical cyclone on record, Tip was the largest cyclone on record, with
tropical storm-force winds 2,170 kilometres (1,350 mi) in diameter. The smallest storm on record,Tropical
Storm Marco, formed during October 2008, and made landfall in Veracruz. Marco generated tropical storm-
force winds only 37 kilometres (23 mi) in diameter.[123]
Hurricane John is the longest-lasting tropical cyclone on record, lasting 31 days in 1994. Before the advent of
satellite imagery in 1961, however, many tropical cyclones were underestimated in their durations. [124] John is
also the longest-tracked tropical cyclone in the Northern Hemisphere on record, which had a path of
7,165 miles (13,280 km). Reliable data for Southern Hemisphere cyclones is unavailable.[125]

26. [edit]Changes caused by El Niño-Southern Oscillation
See also: El Niño-Southern Oscillation
Most tropical cyclones form on the side of the subtropical ridge closer to the equator, then move poleward past
the ridge axis before recurving into the main belt of the Westerlies.[126] When thesubtropical ridge position shifts
due to El Niño, so will the preferred tropical cyclone tracks. Areas west of Japan and Korea tend to experience
much fewer September–November tropical cyclone impacts during El Niño and neutral years. During El Niño
years, the break in the subtropical ridge tends to lie near 130°E which would favor the Japanese
archipelago.[127] During El Niño years, Guam's chance of a tropical cyclone impact is one-third of the long term
average.[128] The tropical Atlantic ocean experiences depressed activity due to increased vertical wind
shear across the region during El Niño years.[129] During La Niña years, the formation of tropical cyclones, along
with the subtropical ridge position, shifts westward across the western Pacific ocean, which increases the
landfall threat toChina.[127]
[edit]Long-term activity trends
See also: Atlantic hurricane reanalysis
Atlantic Multidecadal Cycle since 1950, usingaccumulated cyclone energy (ACE)
Atlantic Multidecadal Oscillation Timeseries, 1856–2009
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

27. remains about 87 ± 10 (Between 77 and 97 tropical cyclones annually).
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.[130] 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 years or so, corresponding to
about a 15% increase in the maximum wind speed and a 60% increase in
storm lifetime."[131]
Atlantic storms are becoming more destructive financially, since five of the
ten 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 been caused largely by rising
concentrations of population and infrastructure in coastal
regions.‖[132] 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 billion of normalized damage.[133]
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.[134]
The number and strength of Atlantic hurricanes may undergo a 50–70 year
cycle, also known as theAtlantic Multidecadal Oscillation. Nyberg et
al. reconstructed Atlantic major hurricane activity back to the early 18th

28. century and found five periods averaging 3–5 major hurricanes per year and
lasting 40–60 years, and six other averaging 1.5–2.5 major hurricanes per
year and lasting 10–20 years. 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 1–2 per year.[135]
Although more common since 1995, few above-normal hurricane seasons
occurred during 1970–94.[136] Destructive hurricanes struck frequently from
1926–60, including many major New England hurricanes. Twenty-one Atlantic
tropical storms formed in 1933, a record only recently exceeded in2005, which
saw 28 storms. Tropical hurricanes occurred infrequently during the seasons
of 1900–25; however, many intense storms formed during 1870–99. During
the 1887 season, 19 tropical storms formed, of which a record 4 occurred
after 1 November and 11 strengthened into hurricanes. Few hurricanes
occurred in the 1840s to 1860s; however, many struck in the early 19th
century, including a1821 storm that made a direct hit on New York City. Some
historical weather experts say these storms may have been as high
as Category 4 in strength.[137]
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.[134] 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 paleotempestological research have revealed that
major hurricane activity along the Gulf of Mexico coast varies on timescales of
centuries to millennia.[138][139] 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

29. position of the Azores High,[139] which may also be linked to changes in the
strength of the North Atlantic Oscillation.[140]
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 14C years BP,[141] 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.
[edit]Global warming
See also: Effects of global warming and Hurricane Katrina and global
warming
The U.S. National Oceanic and Atmospheric Administration Geophysical
Fluid Dynamics Laboratoryperformed a simulation to determine if there is
a statistical 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".[142]
In an article in Nature, meteorology professor 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,
includingmultidecadal 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".[143] In more recent

30. work published by Emanuel (in the March 2008 issue of the Bulletin of the
American Meteorological Society), he states that new climate modeling
data indicates ―global warming should reduce the global frequency of
hurricanes.‖[144] According to the Houston Chronicle, the new work
suggests that, even in a dramatically warming world, hurricane frequency
and intensity may not substantially rise during the next two centuries.[145]
Likewise, P.J. Webster and others published an article
in Science examining the "changes in tropical cyclone number, duration,
and intensity" over the past 35 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
cyclo
nes.[1 Costliest U.S. Atlantic hurricanes
46]
Total estimated property damage, adjusted for wealth normalization[133]
Rank Hurricane Season Cost (2005 USD)
The 1 "Miami" 1926 $157 billion
stren 2 "Galveston" 1900 $99.4 billion
gth 3 Katrina 2005 $81.0 billion
4 "Galveston" 1915 $68.0 billion
of
5 Andrew 1992 $55.8 billion
the
6 "New England" 1938 $39.2 billion
repor
7 "Cuba–Florida" 1944 $38.7 billion
ted
8 "Okeechobee" 1928 $33.6 billion
effect
9 Donna 1960 $26.8 billion
is
10 Camille 1969 $21.2 billion
surpr Main article: List of costliest Atlantic hurricanes
ising
in light of modeling studies[147] that predict only a one-half category
increase in storm intensity as a result of a ~2 °C (3.6 °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 ~75–120% increase he reported.[143] Second, 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.[133][148]

31. Sufficiently warm sea surface temperatures are considered vital to the
development of tropical cyclones.[149] 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 natural
variability, e.g. the hypothesized Atlantic Multidecadal Oscillation(AMO),
although an exact attribution has not been defined.[150] However, recent
temperatures are the warmest ever observed for many ocean basins.[143]
In February 2007, the United Nations Intergovernmental Panel on
Climate Change released its 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. In addition,
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.[151] 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".[152] A statement by
the American Meteorological Society on 1 February 2007 stated that
trends in tropical cyclone records offer "evidence both for and against the
existence of a detectable anthropogenic signal" in tropical
cyclogenesis.[153] Although many aspects of a link between tropical
cyclones and global warming are still being "hotly debated",[154] a point of
agreement is that no individual tropical cyclone or season can be
attributed to global warming.[150][154] Research reported in the 3
September 2008 issue of Nature found that the strongest tropical
cyclones are getting stronger, in particular over the North Atlantic and
Indian oceans. Wind speeds for the strongest tropical storms increased
from an average of 140 miles per hour (230 km/h) in 1981 to 156 miles
per hour (251 km/h) in 2006, while the ocean temperature, averaged
globally over the all regions where tropical cyclones form, increased
from28.2 °C (82.8 °F) to 28.5 °C (83.3 °F) during this period.[155][156]

32. [edit]Related cyclone types
Subtropical Storm Gustav in 2002
See also: Cyclone, Extratropical cyclone, andSubtropical cyclone
In addition to tropical cyclones, there are two other classes of cyclones
within the spectrum of cyclone types. These kinds of cyclones, known
asextratropical cyclones and subtropical cyclones, can be stages a
tropical cyclone passes through during itsformation or
dissipation.[157] An extratropical cycloneis 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; although
not as frequently, an extratropical cyclone can transform into a
subtropical storm, and from there into a tropical cyclone.[158] From space,
extratropical storms have a characteristic "comma-shaped" cloud
pattern.[159] Extratropical cyclones can also be dangerous when their low-
pressure centers cause powerful winds and high seas.[160]
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 latitudes, from theequator to 50°.
Although subtropical storms rarely have hurricane-force winds, they may
become tropical in nature as their cores warm.[161] From an operational

33. standpoint, a tropical cyclone is usually not considered to become
subtropical during its extratropical transition.[162]
[edit]Tropical cyclones in popular culture
Main article: Tropical cyclones in popular culture
In popular culture, tropical cyclones have made appearances in different
types of media, including films, books, television, music, and electronic
games. The media can have tropical cyclones that are entirely fictional, or
can be based on real events.[163] For example, George Rippey
Stewart's Storm, abest-seller published in 1941, is thought to have
influenced meteorologists into giving female names to Pacific tropical
cyclones.[164] Another example is the hurricane in The Perfect Storm,
which describes the sinking of the Andrea Gail by the 1991 Perfect
Storm.[165] Also, hypothetical hurricanes have been featured in parts of
the plots of series such as The Simpsons, Invasion, Family
Guy, Seinfeld,Dawson's Creek, and CSI: Miami.[163][166][167][168][169][170] The
2004 film The Day After Tomorrowincludes several mentions of actual
tropical cyclones as well as featuring fantastical "hurricane-like" non-
tropical Arctic storms.[171][172]
[edit]See also
 Outline of tropical cyclones Tropical cyclones portal
 Cyclone
 Disaster preparedness  Hypercane
 HURDAT (online database)  List of wettest tropical cyclones by country
 Hurricane Alley  Secondary flow in tropical cyclones
 Saffir–Simpson Hurricane Scale
Annual seasons Forecasting and preparation
 List of Atlantic hurricane seasons (current)  Catastrophe modeling
 List of North Indian Ocean cyclone seasons(current)  Hurricane engineering
 List of Pacific hurricane seasons (current)  Hurricane preparedness
 List of Pacific typhoon seasons (current)  Hurricane-proof building
 List of South-West Indian Ocean cyclone  Tropical cyclone watches and warnings
seasons (current)

34.  List of Australian region cyclone seasons(current)
 List of South Pacific cyclone seasons (current)
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