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(Courtesy NOAA)

What is a Hurricane?

Hurricanes are large tropical storms that form in the Atlantic Ocean in which winds exceed 119 kilometers per hour (74 mph). They usually form in the tropics when ocean temperatures reach about 26.5ºC (80ºF). Hurricanes are called typhoons in the western Pacific and cyclones in the Indian Ocean.

The exact mechanism behind hurricane formation is not fully understood, but they generally start as a low pressure system containing warm, moist air. The warm air rises and releases its heat and moisture to the atmosphere.

At the same time, the moisture cools and condenses, forming clouds and bands of rain or thunderstorms. The column of rising air acts like a chimney, drawing additional warm, moisture-laden air upward. The coriolis effect starts to rotate the rising air and clouds creating strong winds.

Energy released from the condensation of the rising, moist air literally fuels the hurricane. This explains why a hurricane weakens considerably when it passes over land: its supply of warm, moist air from the ocean is cut off.