Tropical cyclones

Tropical cyclones

Cyclones are large areas of swirling air with clouds and precipitation being formed inside.



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Tropical cyclones

Many cyclones are formed in the region of the tropics, above the thermal equator. Warm air raises so fast there that it starts to swirl. When a vortex breaks free, it becomes a tropical cyclone.

In cyclones the air circulates inwards, in a counterclockwise direction in the northern hemisphere, and a clockwise direction in the southern hemisphere. Air gets very dense inside and it can only move upwards. As the warm air moves upwards fast, it cools down rapidly, its vapor content condenses, thus clouds and precipitation is formed.

Definitions of terms:
Cyclone: a low-pressure atmospheric formation (with pressure decreasing towards the center) characterized by inward-spiraling winds that blow counterclockwise in the Northern Hemisphere.

Typhoon: tropical cyclone formed above the Pacific Ocean.

Hurricane: tropical cyclone formed above the Atlantic Ocean.

Tropical cyclones formed above the Indian Ocean are simply called tropical cyclones.

  • - The area with the lowest air pressure. A wind- and cloud-free area with a diameter of several kilometers to hundreds of kilometers.


Tropical cyclones are amongst the most destructive weather phenomena. They form exclusively over tropical seas and oceans, usually between 10 and 20 degrees latitude.

Each year around 50 tropical cyclones form on the Earth; from May to November in the Northern Hemisphere and from November to May in the Southern Hemisphere. Their names are assigned in alphabetical order, previously they were only given female names but nowadays male names are also used. Today one of the best-known tropical cyclones is Hurricane Katrina, which brought devastating damage to the city of New Orleans.

A tropical cyclone is a rapidly rotating, strong wind system characterized by an extremely low-pressure center. A tropical cyclone is made up of spiral bands, or a spiral of clouds. The density of these clouds is the highest around the eye, where the spiral bands meet. Tropical cyclones do not only spin in place but are also steered westward. Although the wind is highly intense inside cyclones, they travel relatively slowly. The life cycle of cyclones depends on how long they stay over warm waters, and once they reach the coastline, they lose their strength quickly.

Above the ocean, the lower layer of the atmosphere warms up, then rises. The rising air causes a low-pressure area to develop on the surface level. Air spirals in towards the center of the tropical cyclone in a counterclockwise-direction in the Northern Hemisphere and in a clockwise-direction in the Southern Hemisphere due to the Coriolis effect caused by the Earth’s rotation.

The air rising in the center of the cyclone spreads in the troposphere. Since this rising air is warmer than its surroundings, the cold air descends in the center and a cloud-free area is formed, known as the cyclone’s eye. The eyewall has the most intense weather conditions and therefore it is the most destructive; the intensity of tropical cyclones is measured here. These devastating cyclones produce heavy rains and up to 500 mm (19.69 in) of precipitation in a day.

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