In the rest of this article, the term hurricane refers to all such storms. Hurricanes require a special set of conditions, including ample heat and moisture, that exist primarily over warm tropical oceans. Warm seawater evaporates and is absorbed by the surrounding air. The warmer the ocean, the more water evaporates. The warm, moist air rises, lowering the atmospheric pressure of the air beneath.
Air tends to move from areas of high pressure to areas of low pressure, creating wind.
In the Northern Hemisphere, the earth's rotation causes the wind to swirl into a low-pressure area in a counterclockwise direction. In the Southern Hemisphere, the winds rotate clockwise around a low. This effect of the rotating earth on wind flow is called the Coriolis effect. The Coriolis effect increases in intensity farther from the equator. To produce a hurricane, a low-pressure area must be more than 5 degrees of latitude north or south of the equator.