Tropical cyclone

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A strong Category 5 hurricane in the Gulf of Mexico.

A tropical cyclone is a cyclonic weather system. (The word "cyclonic" means it has a circle-like shape.) Hurricanes start over the ocean in the tropics and move towards higher latitudes. Hurricanes are dangerous. They can make a lot of damage.

1 Terms
2 Formation
- 2.1 Locations and times
- 2.2 Dissipation
3 Naming
4 Impact
5 What They Are Called Around The World
6 Related topics
7 External links
- 7.1 Official forecasters
- 7.2 Other

[edit] Terms

A tropical cyclone is a low pressure system and a cyclonic storm found in the tropics on Earth. There are several names for tropical cyclones, depending on where they happen: "tropical depressions", "tropical storms", and "hurricanes", along with other terms used in different places on Earth such as "cyclones" and "typhoons".

When winds get faster than 117 km/h or 75 mph, tropical cyclones are called "hurricanes" in the Northern Atlantic Ocean and Eastern and Central Pacific Ocean east of the international dateline. They are called "typhoons" or sometimes "super typhoons" in the Pacific Ocean west of the dateline. They are known as "cyclonic storms" in the North Indian Ocean and just "cyclones" in the Southern hemisphere.

[edit] Formation

A rare tropical cyclone in the south Atlantic

A tropical cyclone forms in the tropical latitudes when moist, hot air rises. It starts out as a cluster of thunderstorms when water temperatures reach 80 degrees or hotter. It then begins to slowly organize and look like a spiral shape. When convection bursts happen and a low-level circulation reaches the surface, it is then called a tropical disturbance.

But when winds reach at least 25 mph, it is then called a "tropical depression". If a tropical depression strengthens with maximum sustained winds of 40 mph, it is then called a "tropical storm". Tropical storms can turn into hurricanes (or typhoons and cyclones) when winds reach 75 mph. Tropical cyclones can form in the Atlantic Ocean, the Pacific Ocean, the Indian Ocean, and in some parts of the southern hemisphere.

The Coriolis effect causes circulation. Because of this, tropical cyclones rarely form close to the equator. Areas with cold waters, high upper-level wind shear, and/or dry air do not see any tropical development.

[edit] Locations and times

A tropical cyclone in the Pacific Ocean on August 24, 2002

Tropical cyclones form in the north Atlantic, northern Pacific Ocean, southwestern Pacific, and Indian Ocean. Tropical cyclones may rarely form elsewhere in the world.

The Atlantic Ocean has around ten hurricanes each year. They can hit Central America, Mexico, the United States, Canada, Bermuda Island, and the Caribbean Islands. Most hurricanes form between June and November. Rarely, tropical cyclones form in the south Atlantic.

The northeastern Pacific has around sixteen cyclones a year. Most do not hit land. They rarely affect Mexico, Central America, California, and Hawaii. Most form between May and November.

The northwestern Pacific has around twenty-seven cyclones per year. They can hit Japan, China, North and South Korea, Taiwan, the Philippines, and some Pacific islands. This area has typhoons year-round.

The northern Indian Ocean has around six cyclones each year. They hit India, Bangladesh, Pakistan, and nearby countries. Cyclones form year-round in this area.

The southern Indian Ocean has around twenty-one cyclones each year. They can hit Australia, Indonesia, Madagascar, and southern Africa. Most cyclones form between October and May.

The southwest Pacific has around ten cyclones per year. They can hit some Pacific Islands, Australia, and New Zealand. Most cyclones form between October and May.

[edit] Dissipation

Tropical cyclones can dissipate (break apart and disappear) for several reasons. If they move over land, they no longer get moisture from the ocean waters. But sometimes, tropical cyclones can move over colder waters and begin to become an extratropical cyclone. Sometimes, they may be swallowed up by a larger system (like another stronger tropical cyclone, or another extratropical system). They may run into wind shear, which destroys convection and tears apart the system.

[edit] Naming

A tropical cyclone in the Indian Ocean

Tropical cyclones are usually given names, because this 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.

The Atlantic uses a list of twenty-one names, starting with all letters of the alphabet except Q, V, X, Y, and Z. Names switch between male and female, and are taken from the English, Spanish and French languages. Lists repeat every six years. Destructive or deadly hurricanes have their names "retired". When a name is retired, it is removed from the list and replaced by a new name of the same gender. The eastern Pacific used a similar system of lists, but also with names starting in X, Y, and Z. In both the Atlantic and Pacific, if more cyclones form then there are names, the Greek alphabet is used to name more cyclones.

The central Pacific uses four lists of Hawaiian names. They are used in order without regard to the year.

The western Pacific uses five lists of twenty-eight names. Each country on the committee offers two names. The names are used in order of the countries' English names without regard to year. Names are also retired from these lists.

The areas around Australia use three separate sets. The south Pacific near Fiji uses another set. All are used without regard to year. Names can also be retired.

The southwestern Indian Ocean uses a list of twenty-six names. A new list is used each year. If the number of cyclones is higher than the number of names, more cyclones are not named.

[edit] Impact

Damage from a tropical cyclone

Tropical cyclones, when they make landfall, bring storm surges, high winds, heavy rain, and tornadoes. Heavy rains cause flooding and mudslides. Storm surges flood coastal areas. Winds can blow down trees or destroy power lines. Tropical cyclones can kill people and cause major destruction with millions of dollars in damage if people are not prepared for them.