Tropical Storm in General

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					Tropical cyclone
"Hurricane" redirects here. For other uses, see Hurricane (disambiguation).




Hurricane Isabel (2003) as seen from orbit during Expedition 7 of the International Space Station. The
eye, eyewall and surrounding rainbands that are characteristics of tropical cyclones are clearly visible
in this view from space.

A tropical cyclone is a storm system characterized by a large low-pressure center and numerous
thunderstorms that produce strong winds and heavy rain. Tropical cyclones feed on heat released when
moist air 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 as nor'easters, European windstorms,
and polar lows, 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 tropical regions of the globe, and their formation in maritime tropical air masses. The
term "cyclone" refers to such storms' cyclonic nature, with counterclockwise rotation in the Northern
Hemisphere and clockwise rotation in the Southern Hemisphere. Depending on its location and
strength, a tropical cyclone is referred to by 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 as well as spawning tornadoes. They develop over large
bodies of warm water, and lose their strength if they move over land. 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 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 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 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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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 Sunspot theory
        10 Classifications, terminology, and naming
            o 10.1 Intensity classifications
                     10.1.1 Tropical depression
                     10.1.2 Tropical storm
                     10.1.3 Hurricane or typhoon
            o 10.2 Origin of storm terms
            o 10.3 Naming
        11 Notable tropical cyclones
        12 Changes due to El Niño-Southern Oscillation
        13 Long-term activity trends
        14 Global warming
        15 Related cyclone types
        16 Tropical cyclones in popular culture
        17 See also
        18 References
      19 External links



[edit] Physical structure
See also: Eye (cyclone)




Structure of a tropical 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 may
range in size from 3 kilometres (1.9 mi) to 370 kilometres (230 mi) in diameter.[4][5] Intense, mature
tropical cyclones can sometimes exhibit an outward curving of the eyewall's top, making it resemble a
football stadium; this phenomenon is thus sometimes referred to as the stadium effect.[6]

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 10 kilometres (6.2 mi) to 25 kilometres (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 anti-dwarf


  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 two degrees
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 kilometres (207 mi) to 670 kilometres (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 vorticity field decreases to 1×10−5 s−1
from its center.[12][13]

[edit] Mechanics
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 vapor
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.[15] In another way, tropical cyclones could
be viewed as a special type of mesoscale 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 pressure more 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 drives updrafts that
increase the height of the storm clouds, speeding up condensation.[19] This positive feedback loop
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]

What primarily distinguishes tropical cyclones from other meteorological phenomena is deep
convection as a driving force.[22] 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.[22] 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 running. When a tropical cyclone passes over land, it is cut off from its
heat source and its strength diminishes rapidly.[23]




Chart displaying the drop in surface temperature in the Gulf of Mexico as Hurricanes Katrina and 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 because of 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 (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.[24]

Scientists at the US National Center for Atmospheric Research 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][25]

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.[15] This outflow produces high,
thin cirrus clouds 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.[26] 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

                   Basins and WMO Monitoring Institutions[27]


           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 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 Centers (TCWCs) that provide information to
smaller regions.[28] 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.[29] 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.[30] The Canadian Hurricane Center (CHC) issues advisories
on hurricanes and their remnants for Canadian citizens when they affect Canada.[31]

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.[32]

[edit] Formation
Main article: Tropical cyclogenesis
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.




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
whilst November is the only month with all the tropical cyclone basins active.[33]

[edit] Times

In the Northern Atlantic Ocean, a distinct hurricane season occurs from June 1 to November 30,
sharply peaking from late August through September.[33] 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.[34] 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.[33] 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.[33][35]

                                 Season lengths and seasonal averages[33][36]
                                                     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
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.[37] 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);[38] waters of this temperature
cause the overlying atmosphere to be unstable enough to sustain convection and thunderstorms.[39]
Another factor is rapid cooling with height, which allows the release of the heat of condensation that
powers a tropical cyclone.[38] 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.[38] Low amounts of wind shear are needed, as high shear is disruptive to the storm's
circulation.[38] 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.[38] Lastly, a formative tropical cyclone needs a pre-existing
system of disturbed weather, although without a circulation no cyclonic development will take place.[38]
Low-latitude and low-level westerly wind bursts associated with the Madden-Julian oscillation can
create favorable conditions for tropical cyclogenesis by initiating tropical disturbances.[40]

[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.[41][42][43]
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.[44][45][46]

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.[47][48] 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.[47] However, it is possible for tropical cyclones to form
within this boundary as Tropical Storm Vamei did in 2001 and Cyclone Agni in 2004.[49][50]
[edit] Movement and track
[edit] Steering winds

See also: Prevailing winds

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".[51]

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.[51] 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 African coast and towards the Caribbean Sea, North America, and ultimately into the central
Pacific ocean before the waves dampen out.[45] These waves are the precursors to many tropical
cyclones within this region.[44] 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.[52] 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.[53] 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]

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 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.[54] 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.[55]

[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.[56] 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.[56] 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.[56]

[edit] 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.[57]

[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 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.[58] 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.[59] Many
storm fatalities occur in mountainous terrain, as the dying storm unleashes torrential rainfall,[60] leading
to deadly floods and mudslides, similar to those that happened with Hurricane Mitch in 1998.[61]
Additionally, dissipation can occur if a storm remains in the same area of ocean for too long, mixing
the upper 60 metres (200 ft) of water, dropping sea surface temperatures more than 5 °C (9 °F).[62]
Without warm surface water, the storm cannot survive.[63]

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.[64] 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.[65] 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 days.[66] 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 windstorms; Hurricane Iris's
extratropical remnants are an example of such a windstorm from 1995.[67] 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.[65] Studies in the 2000s have
given rise to the hypothesis that large amounts of dust reduce the strength of tropical cyclones.[68]

[edit] Artificial dissipation

In the 1960s and 1970s, the United States government attempted to weaken hurricanes through Project
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.[69] 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.[70] 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.[71] 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.[72]

Other approaches have been suggested over time, including cooling the water under a tropical cyclone
by towing icebergs into the tropical oceans.[73] Other ideas range from covering the ocean in a
substance that inhibits evaporation,[74] 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),[73] or blasting the cyclone apart with nuclear
weapons.[18] Project Cirrus even involved throwing dry ice on a cyclone.[75] 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.[76]

[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.[77] Tropical cyclones stir up water, leaving a cool wake
behind them, which causes the region to be less favorable for subsequent tropical cyclones.[24] On land,
strong winds 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.[78] 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.[79]

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.[80] Tropical cyclones significantly interrupt infrastructure, leading to power outages,
bridge destruction, and the hampering of reconstruction efforts.[80][81]

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.[82] Tropical cyclones also help maintain the global heat balance by moving
warm, moist tropical air to the middle latitudes and polar regions.[83] 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.[84]

[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. 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.[85]

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.[86]

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.[87] 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 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.[88]
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.[89] 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.[90] However, scientists are not as skillful at predicting the intensity of tropical
cyclones.[91] 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] Sunspot theory
A 2010 report correlates low sunspot activity with high cyclonic activity. Fewer sunspots appear to
decrease temperature in the upper atmosphere, creating unstable conditions that help create cyclones.
Analyzing historical data, there had been a 25% chance of at least one hurricane striking the continental
US during a peak sunspot year; a 64% chance during a low sunspot year. In June 2010, the hurricanes
predictors in the US were not using this information.[92]

[edit] Classifications, terminology, and naming
[edit] Intensity classifications

Main article: Tropical cyclone scales
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 the
Beaufort scale, it is referred to as a typhoon; if a tropical storm passes the same benchmark in the
Northeast Pacific Basin, or in the Atlantic, it is called a hurricane.[56] 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".

Additionally, 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 as Hurricane/Typhoon Ioke in 2006); on rare occasions, the reverse will occur.[93] 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.[94]

[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 the Philippines is to name tropical depressions from their own naming convention when
the depressions are within the Philippines' area of responsibility.[95]

[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).[96]

              [hide]Tropical Cyclone Classifications (all winds are 10-minute averages)[97][98]
                                                                                                  NE Pacific
         10-minute                                                                                   &
                        N Indian    SW Indian                               NW           NW
Beaufort sustained                            Australia SW Pacific                                N Atlantic
                         Ocean       Ocean                                 Pacific      Pacific
 scale     winds                               BOM        FMS                                       NHC,
                          IMD         MF                                    JMA         JTWC
          (knots)                                                                                  CHC &
                                                                                                   CPHC
          <28 knots
                                    Trop.
0–6       (32 mph;     Depression
                                    Disturbance
          52 km/h)
                                                                                     Tropical   Tropical
          28–29 knots                                                                Depression Depression
          (32–33
                                                  Tropical   Tropical   Tropical
          mph; 52–54
                                                  Low        Depression Depression
          km/h)       Deep
7                                Depression
          30–33 knots Depression
          (35–38
          mph; 56–61
          km/h)
          34–47 knots
                                    Moderate      Tropical
          (39–54      Cyclonic                               Tropical    Tropical    Tropical     Tropical
8–9                                 Tropical      Cyclone
          mph; 63–87 Storm                                   Cyclone (1) Storm       Storm        Storm
                                    Storm         (1)
          km/h)
          48–55 knots
          (55–63
10
          mph; 89–    Severe        Severe        Tropical               Severe
          102 km/h) Cyclonic                                 Tropical
                                    Tropical      Cyclone                Tropical
                                                             Cyclone (2)
          56–63 knots Storm         Storm         (2)                    Storm
                                                                                                  Hurricane
11        (64–72                                                                     Typhoon
                                                                                                  (1)
          mph; 104–
        117 km/h)
        64–72 knots
        (74–83
        mph; 119–                           Severe
        133 km/h)                                      Severe
                                            Tropical
                                                       Tropical
        73–85 knots                         Cyclone
                                                       Cyclone (3)
        (84–98                 Tropical     (3)                                          Hurricane
        mph; 135–              Cyclone                                                   (2)
        157 km/h)
        86–89 knots
        (99–102
        mph; 159–
        165 km/h)                                                                        Major
                                                                                         Hurricane
        90–99 knots                                                                      (3)
                                            Severe
        (100–114                                       Severe
                    Very                    Tropical
        mph; 170–                                      Tropical
                    Severe                  Cyclone
        183 km/h)                                      Cyclone (4)
                    Cyclonic                (4)
12      100–106     Storm                                            Typhoon
        knots (120–
                               Intense
        122 mph;
                               Tropical
        190–196
                               Cyclone
        km/h)
        107–114
        knots (123–                                                                      Major
        131 mph;                                                                         Hurricane
        198–211                                                                          (4)
        km/h)
                                            Severe
        115–119                                        Severe
                                            Tropical
        knots (132–                                    Tropical
                                            Cyclone
        137 mph;                                       Cyclone (5)
        213–220                Very Intense (5)
                                                                               Super
        km/h)                  Tropical
                                                                               Typhoon
                               Cyclone
        >120 knots Super                                                                 Major
        (140 mph; Cyclonic                                                               Hurricane
        220 km/h) Storm                                                                  (5)

[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 Urdu, Persian
and Arabic ţūfān (‫ ,)نافوط‬which in turn originates from Greek tuphōn (Τυφών), a monster in Greek
mythology responsible for hot winds.[99] The related Portuguese word tufão, used in Portuguese for
typhoons, is also derived from Greek tuphōn.[100] It is also similar to Chinese "taifeng" ("toifung" in
Cantonese) (颱風 – literally great winds), and also to the Japanese "taifu" (台風), which may explain
why "typhoon" came to be used for East Asian cyclones.[citation needed]

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 huracán.[101] (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.

[edit] Naming

Main articles: Tropical cyclone naming and 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.[102] 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.

[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[103] and potentially as many as 1 million[104] 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.[103] The North Indian cyclone basin has historically
been the deadliest basin.[80][105] 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.[106] The Great Hurricane of
1780 is the deadliest Atlantic hurricane on record, killing about 22,000 people in the Lesser
Antilles.[107] 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,[108] while in 1982, the unnamed tropical depression that eventually
became Hurricane Paul killed around 1,000 people in Central America.[109]

Hurricane Katrina is estimated as the costliest tropical cyclone worldwide,[110] causing $81.2 billion in
property damage (2008 USD)[111] with overall damage estimates exceeding $100 billion
(2005 USD).[110] Katrina killed at least 1,836 people after striking Louisiana and Mississippi as a major
hurricane in August 2005.[111] 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.[112] 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.[113]
Other destructive Eastern Pacific hurricanes include Pauline and Kenna, both causing severe damage
after striking Mexico as major hurricanes.[114][115] 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 years.[116]




The relative sizes of Typhoon Tip, Cyclone Tracy, and the Contiguous 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 (25.69 inHg) and maximum sustained wind speeds of
165 knots (85 m/s) or 190 miles per hour (310 km/h).[117] Tip, however, does not solely hold the record
for fastest sustained winds in a cyclone. Typhoon Keith in the Pacific and Hurricanes Camille and
Allen in the North Atlantic currently share this record with Tip.[118] 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.[119] 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.[96] Similarly, 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 the anemometer was damaged by the storm.[120]

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.[121]

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.[122] 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.[123]

[edit] Changes due to 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.[124] When the
subtropical ridge position shifts due to El Nino, 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.[125] During El Niño years, Guam's chance of a
tropical cyclone impact is one-third of the long term average.[126] The tropical Atlantic ocean
experiences depressed activity due to increased vertical wind shear across the region during El Niño
years.[127] 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 to
China.[125]

[edit] Long-term activity trends
Atlantic Multidecadal Cycle since 1950, using accumulated cyclone energy (ACE)




Atlantic Multidecadal Oscillation Timeseries, 1856–2009
       See also: 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 ± 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.[128] 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."[129]

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 largely been caused by
rising concentrations of population and infrastructure in coastal regions.‖[130] 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.[131]

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.[132]

The number and strength of Atlantic hurricanes may undergo a 50–70 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 3–5 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.[133]
Although more common since 1995, few above-normal hurricane seasons occurred during 1970–
94.[134] 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 in
2005, 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 a
1821 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.[135]

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.[132] 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.[136][137] 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,[137] which may also be linked to changes in the strength of the North Atlantic
Oscillation.[138]

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,[139] 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

The U.S. National Oceanic and Atmospheric Administration Geophysical Fluid Dynamics Laboratory
performed 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".[140]

In an article in 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".[141] In more recent 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.‖[142] 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.[143]

Similarly, 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 cyclones.[144]

The strength of the reported effect is                    Costliest U.S. Atlantic hurricanes
surprising in light of modeling             Total estimated property damage, adjusted for wealth normalization[131]
studies[145] that predict only a one half    Rank        Hurricane            Season      Cost (2005 USD)
category increase in storm intensity as a      1     "Miami"                 1926       $157 billion
result of a ~2 °C (3.6 °F) global
warming. Such a response would have            2     "Galveston"             1900       $99.4 billion
predicted only a ~10% increase in              3     Katrina                 2005       $81.0 billion
Emanuel's potential destructiveness            4     "Galveston"             1915       $68.0 billion
index during the 20th century rather           5     Andrew                  1992       $55.8 billion
than the ~75–120% increase he
                                               6     "New England"           1938       $39.2 billion
reported.[141] Secondly, after adjusting
for changes in population and inflation,       7     "Cuba–Florida"          1944       $38.7 billion
and despite a more than 100% increase          8     "Okeechobee"            1928       $33.6 billion
in Emanuel's potential destructiveness         9     Donna                   1960       $26.8 billion
index, no statistically significant           10     Camille                 1969       $21.2 billion
increase in the monetary damages
                                                     Main article: List of costliest Atlantic hurricanes
resulting from Atlantic hurricanes has
been found.[131][146]

Sufficiently warm sea surface temperatures are considered vital to the development of tropical
cyclones.[147] 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.[148] However, recent temperatures are the warmest ever observed for many ocean basins.[141]

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.
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.[149] 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".[150] 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.[151] Although many aspects of a link between tropical cyclones and global warming are
still being "hotly debated",[152] a point of agreement is that no individual tropical cyclone or season can
be attributed to global warming.[148][152] Research reported in the 3 September 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 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 from 28.2 °C (82.8 °F)
to 28.5 °C (83.3 °F) during this period.[153][154]

[edit] Related cyclone types




Subtropical Storm Gustav in 2002
See also: Cyclone, Extratropical cyclone, and 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 cyclones and subtropical cyclones, can be stages
a tropical cyclone passes through during its formation or dissipation.[155] 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;
additionally, although not as frequently, an extratropical cyclone can transform into a subtropical
storm, and from there into a tropical cyclone.[156] From space, extratropical storms have a characteristic
"comma-shaped" cloud pattern.[157] Extratropical cyclones can also be dangerous when their low-
pressure centers cause powerful winds and high seas.[158]

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 the equator
to 50°. Although subtropical storms rarely have hurricane-force winds, they may become tropical in
nature as their cores warm.[159] From an operational standpoint, a tropical cyclone is usually not
considered to become subtropical during its extratropical transition.[160]

[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.[161] For example, George Rippey Stewart's Storm, a
best-seller published in 1941, is thought to have influenced meteorologists into giving female names to
Pacific tropical cyclones.[162] Another example is the hurricane in The Perfect Storm, which describes
the sinking of the Andrea Gail by the 1991 Perfect Storm.[163] 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.[161][164][165][166][167][168] 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.[169][170]

[edit] See also
           Tropical cyclones portal

          Cyclone                                      Hypercane
          Disaster preparedness                        List of wettest tropical cyclones by country
          HURDAT (online database)                     Secondary flow in tropical cyclones
          Hurricane Alley
          Saffir–Simpson Hurricane Scale

Annual seasons                                        Forecasting and preparation

      List of Atlantic hurricane seasons (current)         Catastrophe modeling
      List of North Indian Ocean cyclone seasons           Hurricane engineering
       (current)                                            Hurricane preparedness
      List of Pacific hurricane seasons (current)          Hurricane-proof building
      List of Pacific typhoon seasons (current)            Tropical cyclone watches and warnings
      List of South-West Indian Ocean cyclone
       seasons (current)
      List of Australian region cyclone seasons
       (current)
     List of South Pacific cyclone seasons
      (current)


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[edit] External links

      Look up tropical cyclone in Wiktionary, the free dictionary.
          Wikimedia Commons has media related to: Tropical cyclones

Regional Specialized Meteorological Centers

         US National Hurricane Center – North Atlantic, Eastern Pacific
         Central Pacific Hurricane Center – Central Pacific
         Japan Meteorological Agency – NW Pacific
         India Meteorological Department – Bay of Bengal and the Arabian Sea
         Japan Meteorological Agency – NW Pacific
         Météo-France – La Reunion – South Indian Ocean from 30°E to 90°E
         Fiji Meteorological Service – South Pacific west of 160°E, north of 25° S

Tropical Cyclone Warning Centers

         Indonesian Meteorological Department – South Indian Ocean from 90°E to 125°E, north of
          10°S
         Australian Bureau of Meteorology (TCWC's Perth, Darwin & Brisbane). – South Indian Ocean
          & South Pacific Ocean from 90°E to 160°E, south of 10°S
         Meteorological Service of New Zealand Limited – South Pacific west of 160°E, south of 25°S

Reference

         Hurricane Glossary of Terms

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