Day after day the fluffy cumuli form atop the updrafts, but the cloud tops rarely rise higher than about 6,000 feet. At that height in the tropics, there is usually a layer of warm, dry air that acts like an invisible ceiling or lid. Once in a while, something happens in the upper air that destroys this lid. Scientist do not know how this happens, but when it does, it's the first step in the birth of a hurricane. With the lid off, the warm, moist air rises higher and higher.
Heat energy is released as the water vapor in the air condenses.
As it condenses it drives the upper drafts to heights of 50,000 to 60,000 feet. The cumuli become towering thunderheads. From outside the storm area, air moves in over the sea surface to replace the air soaring upwards in the thunderheads. The air begins swirling around the storm center, for the same reason that the air swirls around a tornado center. As this air swirls in over the sea surface, it soaks up more and more water vapor.