How do hurricanes form?
A hurricane is a giant storm engine powered by warm ocean water, roughly 80°F or warmer. Water evaporates, rises, and condenses into storms that release huge amounts of heat, which pulls in more moist air. Earth's spin turns the whole thing into a rotating system.
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What feeds them
Warm water evaporates into the air above it. When that moist air rises and condenses into clouds, it releases the heat it took to evaporate, warming the air and making it rise even faster. Surface pressure drops, more air rushes in across the warm water, and the cycle feeds itself. Light winds high up let the storm stack vertically and strengthen.
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Why they spin, and the eye
Air rushing toward the low pressure is turned by Earth's rotation, counterclockwise in the Northern Hemisphere. That's also why hurricanes almost never form within about 5 degrees of the equator, where the effect is too weak. In a strong storm, air sinking in the center clears out a calm eye, surrounded by the eyewall, where the strongest winds and heaviest rain are.
Season and danger
The Atlantic season runs June 1 to November 30, peaking in early to mid September when the ocean is warmest. The Saffir-Simpson scale rates hurricanes from Category 1 (74 mph winds) to Category 5 (157 mph or more), but water is usually the deadliest part: storm surge along the coast and flooding rain inland.
Questions people ask
- Why do hurricanes weaken over land?
- They lose their supply of warm, moist air, and friction with land slows them down. They can still cause severe inland flooding.
- Hurricane, typhoon, cyclone: what's the difference?
- Same kind of storm, different ocean: hurricane in the Atlantic and eastern Pacific, typhoon in the western Pacific, cyclone in the Indian Ocean and South Pacific.