Hurricanes are large weather engines, and any engine needs energy to run.
The secret energy source of a hurricane is the large latent heat of water. Air over the tropical oceans is drier than you might think. Although both the air and water may be warm and calm, evaporation can take place because the air is not at 100 percent relative humidity.
Silently and invisibly, water changes from liquid to vapor and enters the atmosphere. The energy required to make this change comes from the sun, and this energy is lying in wait — latent — ready to be released when the vapor is condensed into liquid again. This happens in rising air in a cloud or thunderstorm.
However, this process alone is not enough to power a hurricane. A hurricane adds fuel to its own fire by drawing surface air toward its low-pressure center. The tight pressure gradient nearer the center means that the winds grow stronger as the air approaches the eye. The faster the wind blows, the more evaporation takes place (this is why you blow-dry wet hair or hands instead of merely warming them).
Increased evaporation means more water vapor in the air and more energy ready to be liberated in the hurricane’s thunderstorms as water vapor condenses. In short, evaporation and condensation of water are the keys to understanding the power of tropical cyclones.
How strong is the engine that powers a tropical cyclone? The energy released by condensation in a single day in an average hurricane is at least 200 times the entire world’s electrical energy production capacity. Part of this energy is expended reducing the central pressure of the storm and strengthening the winds.