For millennia, we saw the oceans as mysterious wellsprings of nature's power, capable of rising up and engulfing us. The history books are filled with stories of cities and towns caught off guard by the sudden onrush of a tropical storm.
We now see hurricanes, typhoons, and cyclones as the product of climate systems on a much larger scale... water and wind, oceans and land. They are fueled by heat from the sun, captured and stored in the upper layer of tropical oceans. The deeper and warmer this upper layer becomes, the stronger and longer lasting a hurricane can be.
In the Atlantic Ocean, they often begin their lives over mountains in East Africa. As the wind sweeps over them, an area of low pressure forms. It travels across the Sahara Desert, then moves out over the warm Atlantic. There, it can spawn thunderstorms over a broad region. As the low gradually comes under the influence of the Earth's rotation, called the Coriolis force, it begins to spin.
As the storm intensifies, the pressure in its center continues to drop, forming what's known as "the eye." It acts like a partial vacuum, causing winds at the sea surface to spiral inward toward it. These in-spiraling winds evaporate moisture from the warm ocean surface. As they near the eye, they veer upward, producing clouds and rain.
Much of this air moves outward at the top of the storm, like a chimney. Some flows back down into the center, causing the eye to dry out and become clear. The path a hurricane takes, and the intensity it reaches, are determined by its interaction with global weather systems and ocean currents. In most cases, they form in vast ocean areas along the equator, pushed along by equatorial wind currents.
At higher latitudes, to the north and south, east-bound winds circle the globe. Where they converge in the tropics, the flow shifts to the west, forming the trade winds and a band of precipitation called the Inter-tropical Convergence Zone. Stretching all around the Earth, this is the breeding ground for countless thunderstorms and larger tropical storms.