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Tropical Cyclone Formation

Hurricane Gert

Hurricane Gert approaching the Avalon Peninsula of Newfoundland, September 22, 1999

Tropical Cyclones (known as hurricanes and tropical storms in the Atlantic Ocean, typhoons in the Pacific Ocean and cyclones in the Indian Ocean) can be a very powerful and destructive type of storm. This type of storm develops over oceans 8° to 15° North and South of the equator.

In order for tropical cyclones to form, there are several environmental conditions that must be present:

    1) The cyclone must originate over ocean water that is least 26.5 °C. Hurricanes draw their energy from the warm water of the tropics and latent heat of condensation.

    2) There must be an atmosphere that cools quickly with height so that it is potentially unstable. If the air is unstable, it will continue rising and the disturbance will grow. The disturbance will only grow when winds at all levels of the atmosphere from the ocean up to 30,000 feet or higher are blowing at the same speed and from the same direction. In other words, there must be low values of vertical wind shear.

    3) The cyclone will not form closer than approximately 500 kilometres to the equator because the Coriolis Force is too weak. It is the Coriolis Force (an effect that results from the turning of the earth) that initially makes the cyclone spiral and maintains the low pressure of the disturbance.

    4) An upper atmosphere high pressure area above the growing storm should be present. The air in such high pressure areas is flowing outward. This pushes away the air that is rising in the storm, which encourages even more air to rise from the low levels.

Hurricanes will not always form if these conditions are present. However, a hurricane will only form if these conditions are present.



Parts of a Tropical Cyclone

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2003-09-18