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hurricane
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| A section through a hurricane. Air
violently spirals around a calm "eye", strong updrafts giving rise
to heavy rain |
A tropical cyclone, usually of great intensity. High-speed winds spiral in toward a low-pressure core of warm, calm air (the eye); winds of over 300 km/h have been measured. The direction of spiral is clockwise in the Southern Hemisphere, counterclockwise in the North (see Coriolis effect).
Hurricanes form (usually between latitudes 5° and 25°) when there is an existing convergence of air near sea level toward a center. The air ascends, losing moisture as precipitation as it does so. If this happens rapidly enough, the upper air is warmed by the water's latent heat of vaporization. This reduces the surface pressure, so accelerating air convergence.
Hurricanes of the North Pacific are often called typhoons.
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| Hurricane seen from space
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