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Tropical cyclone

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Tropical cyclone or hurricane is a circular air movement over the warm ocean waters in the warm part of Earth near the equator. Most tropical cyclones create strong winds and heavy rains. While some tropical cyclones stay out in the sea, others pass over land, which can be dangerous because they can cause a lot of damage.

Hurricane Rita 24 hours after its peak intensity

Tropical cyclones form when warm, moist ocean air rises. They begin as a group of storm winds when the water gets as hot as 80 degrees F (27 C) or hotter. The Coriolis effect causes the winds to rotate. They usually move westward in the tropics, and later move north or south into the temperate zone. Tropical cyclones that form in the Atlantic are called "hurricanes". Those in Pacific are called "typhoons", and in the Indian Ocean they are called "cyclones".


See also: Lists of tropical cyclone names

Tropical cyclones are usually given names because it helps in forecasting, tracking, and reporting. They are named once they have steady winds of 62 km/h. Committees of the World Meteorological Organization pick names. Once named, a cyclone is usually not renamed.[1]


Gulfport, Mississippi: damaged city struck by Hurricane Katrina, 2005.

In the past these storms sank many ships. Better weather forecasting in the 20th century let most ships avoid them. When tropical cyclones reach land, they may break things. Sometimes they kill people and destroy cities. In the last 200 years, about 1.5 million people have been killed by tropical cyclones.

Wind can cause up to 83% of the total damages of a storm. Broken wreckage from destroyed objects can become deadly flying pieces.[2] Flooding can also occur when rainfalls and/or storm surges pour water onto land.[3]

There is a possibility of indirect deaths after a tropical cyclone makes landfall. For example, New Orleans, Louisiana suffered from poor sanitary conditions after Hurricane Katrina hit in 2005.[4]


Saffir–Simpson Hurricane Scale
Category Wind speed Storm surge
5 ≥156
>18 (>5.5)
4 131–155
3 111–130
2 96–110
1 74–95
Additional classifications
See also: Saffir-Simpson Hurricane Scale

Tropical cyclones are classified into different categories depending on their strength and location. The National Hurricane Center which observes hurricanes in the Atlantic Ocean and Eastern and Central Pacific Ocean classify them into the Saffir-Simpson Hurricane Scale.

Tropical cylones in other places such as the Western Pacific Ocean or the Southern Hemisphere are classified on similar scales. For example; if a tropical storm in the western Pacific reaches hurricane-strength winds, it is then officially recognized as a typhoon.

A tropical depression is an organized group of clouds and thunderstorms with a clear surface circulation and maximum sustained winds of less than 17 m/s (33 kt, 38 mph, or 62 km/h). It has no eye and does not usually have the spiral shape of more powerful storms. Only the Philippines are known to name tropical depressions.

A tropical storm is an organized system of strong thunderstorms with a very clear surface circulation and maximum sustained winds between 17 and 32 m/s (34–63 kt, 39–73 mph, or 62–117 km/h). At this point, the cyclonic shape starts to form, although an eye does not usually appear in tropical storms. Most tropical cyclone agencies beginning naming cyclonic storms at this point, except for the Philippines which have their own way of naming cyclones.

A hurricane or typhoon is a cyclonic weather system with sustained winds of at least 33 m/s (64 kt, 74 mph, or 118 km/h). A tropical cyclone of this strength usually develop an eye, an area of calm conditions at the center of circulation. The eye is often seen from space as a small, round, cloud-free spot. Surrounding the eye is the eyewall, an area in which the strongest thunderstorms and winds spin around the storm's center. The fastest sustained windspeed founded in tropical cyclones is thought to be 85 m/s (165 kt, 190 mph, 305 km/h).

Other pages


  1. Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division. "Frequently Asked Questions: What are the upcoming tropical cyclone names?". NationalOAA. Retrieved 2006-12-11.
  2. Chris Landsea. "How does the damage that hurricanes cause increase as a function of wind speed?". Hurricane Research Division. Retrieved 2007-02-24.
  3. James M. Shultz, Jill Russell and Zelde Espinel (2005). "Epidemiology of Tropical Cyclones: The Dynamics of Disaster, Disease, and Development". Oxford Journal. Retrieved 2007-02-24.
  4. Staff Writer (2005-08-30). "Hurricane Katrina Situation Report #11". Office of Electricity Delivery and Energy Reliability (OE) United States Department of Energy. Retrieved 2007-02-24.
Cyclones and Tropical cyclones of the World
Cyclone - Tropical - Extratropical - Subtropical - Mesocyclone - Polar cyclone - Polar low