Hurricanes are intense low pressure areas that form over warm ocean waters in the summer and early fall. Their source of energy is water vapor which is evaporated from the ocean surface.

Water vapor is the "fuel" for the hurricanes because it releases the "latent heat of condensation" when it condenses to form clouds and rain, warming the surrounding air. (This heat energy was absorbed by the water vapor when it was evaporated from the warm ocean surface, cooling the ocean in the process.)

Usually, the heat released in this way in tropical thunderstorms is carried away by wind shear, which blows the top off the thunderstorms. But when there is little wind shear, this heat can build up, causing low pressure to form. The low pressurecauses wind to begin to spiral inward toward the center of the low.