How do hurricanes form?

Hurricanes are giant, rotating tropical storms powered by warm ocean water, and heat is the essential ingredient. They form over tropical seas where the surface water is warm, generally at least about 80 degrees Fahrenheit (27 Celsius), down to a decent depth. The warm ocean heats the air above it, and this warm, moist air rises, creating an area of low pressure at the surface. As the air rises and cools, its water vapor condenses into clouds and releases heat, which warms the surrounding air and makes it rise even faster, drawing in more warm moist air from the ocean surface below. This becomes a self-reinforcing engine: rising air, condensation, released heat, more rising air, pulling in ever more warm ocean moisture as fuel. The Earth's rotation (the Coriolis effect) sets the whole system spinning, counterclockwise in the Northern Hemisphere, and if conditions stay favorable, the storm organizes into the familiar spiral with a calm eye at the center, surrounded by the violent eyewall of strongest winds.

This dependence on warm water explains almost everything about hurricane behavior. It is why hurricane season falls in the late summer and early fall, when ocean temperatures peak, and why hurricanes form in specific warm tropical regions (the Atlantic, the Caribbean and Gulf, and equivalent basins in the Pacific and elsewhere, where the same storm is called a typhoon or cyclone). It is why hurricanes intensify over warm water and rapidly weaken once they move over land or cooler seas, they get cut off from the warm-ocean fuel that sustains them, so they lose strength quickly after landfall (though they can still cause catastrophic wind, rain, and flooding as they fade). It is also central to concerns about climate change, since warmer oceans provide more fuel, which research links to hurricanes that can intensify faster and carry more rainfall. So a hurricane is essentially a heat engine fed by warm seawater: warm ocean evaporates moisture, rising air and condensation build a spinning, self-feeding storm, and the storm thrives as long as it stays over warm water and dies once it does not.