Hurricanes

Hurricanes

Hurricanes get their start over the warm tropical waters of the North

Atlantic Ocean near the equator. Most hurricanes appear in late summer or

early fall, when sea temperatures are at their highest. The warm waters

heats the air above it, and the updrafts of warm, moist air begin to rise.

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 don 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, 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 vapour. At the storm center, this new supply of water vapor gets

pulled into the thunderhead updrafts, releasing still more energy as the

water vapor condenses. This makes the updrafts rise faster, pulling in

even larger amounts of air and water vapor from the storm's edges. And as

the updrafts speed up, air swirls faster and faster around the storm center.

The storm clouds, moving with the swirling air, form a coil.

In a few days the hurricane will have grown greatly in size and power.

The swirling shape of the winds of the hurricane is shaped like a dough-nut.

At the center of this giant "dough-nut" is a cloudless, hole usually having

a radius of 10 miles. Through it, the blue waters of the ocean can be seen.

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