The moist, hot winds of a hurricane swirl upward around a calm column of low-pressure air known as the eye. Some hurricanes can develop more than one eye, but the largest is always the main eye and measures an average of 15 miles across. Inside the eye there are no storm clouds, almost no wind, and calm conditions. However, beneath this tranquil center is wild, stormy chaos.
The rising winds rotate in increasingly tight spirals around the eye, rising faster and faster. Cooler air is also sucked in, heated, and sent twisting up the eye. When the hot air rises high enough, it cools and forms water droplets that cluster together as clouds and drop rain. The rain is blown around by fierce winds.
Hurricanes were once thought to be shaped like doughnuts, circling around the eye. However, satellite images have shown them more to resemble pinwheels, with thicker clouds near the center and long, thin, trailing ends.
The atmospheric pressure is lowest closest to the eye, making the winds there spin faster. At the storm’s outer edges, they blow more slowly. A hurricane moves west or northwest at an average of ten miles an hour, with a wind radius as large as 100 miles. As it moves, it churns up the sea beneath the eye, sucking ocean water up and creating huge ocean waves. The raised water is carried along by the storm to the shore.
Forces of Nature: ThinkQuest 2000 (Team #C003603)
http://library.thinkquest.org/C003603/english/hurricanes/causesofhurricanes.shtml
Hurricanes can develop when the sun’s rays heat tropical waters to at least 82 degrees Fahrenheit. This causes the air to grow warmer and rise. Water rises with it as vapor, and the heat causes the air to rise faster and faster. In about 12 hours, the heated air will begin to circle counterclockwise, forming stronger and stronger winds that whirl with increasing speed. Air that is motionless is calm. When it moves slowly, it is a light breeze. If it moves slightly faster, it becomes a fresh breeze, and even faster is a high wind. A wind becomes a hurricane when it reaches speeds of more than 74 miles (120 km) per hour. It is unknown what top hurricane speeds are, because instruments have always been destroyed by high winds or flying debris. Some estimate that hurricane winds do not surpass 250 miles (400 km) per hour, while others say they can reach 600 miles (960 km) per hour.