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What is a Hurricane?
Hurricane winds whip palm trees along a South Florida beach.
Photograph by Corbis

Centuries ago the Spanish used huracan, an indigenous word for evil spirits and weather gods, to name the storms that sank their ships in the Caribbean.

Today "hurricane" is one of three names for a rotating tropical storm with winds of at least 74 miles (119 kilometers) an hour.

These storms are called hurricanes when they develop over the Atlantic or eastern Pacific Oceans. They are cyclones when they form over the Bay of Bengal and the northern Indian Ocean, and they are typhoons when they develop in the western Pacific.

Whatever their names, these storms are capable of annihilating coastal areas and causing massive death tolls.

What Causes a Hurricane?
Hurricane Floyd's reach extends far up the U.S. East Coast.
Photograph courtesy NOAA

Conditions have to be just right for a hurricane to form. About a hundred tropical disturbances develop every year, but less than 10 percent lead to anything but thunderstorms.

Most Atlantic Ocean hurricanes form near the Cape Verde Islands off Africa's west coast, where trade winds of the Northern and Southern Hemispheres meet and cause tropical disturbances.

Disturbances take energy from the warm waters to grow into tropical depressions. These are marked by an organized system of thunderstorms and top wind speeds of 38 miles (61 kilometers) an hour.

As the depression moves across the ocean, its energy grows. If its low-pressure center intensifies and its winds move at more than 39 miles (63 kilometers) an hour, the depression becomes a tropical storm and is assigned a name.

Once the storm's winds hit a constant speed of at least 74 miles (119 kilometers) an hour, it becomes a hurricane.

Once a hurricane forms, it has three main parts.

At the middle is the eye, the low-pressure center of the hurricane. The eye is usually between 20 to 30 miles (32 to 48 kilometers) wide. Air sinks inside the eye, clearing the skies and making it relatively calm. This calm often fools people into believing the storm has passed when in fact they are in the middle of it.

The ring-shaped eye wall surrounds the eye. Here are the hurricane's fastest and most violent winds and its most intense rains. Air here moves rapidly toward the center and then suddenly upward, as if it had hit a wall.

Feeder bands are bands of rain showers with gusty winds. Since they are the outermost layer of the hurricane, feeder bands are the first signs of the coming storm.

Hurricanes usually develop in summer and fall, when the ocean temperatures are at their warmest.

Hurricane season in the Atlantic, Caribbean, Gulf of Mexico, and central Pacific is from June 1 to November 30. In the eastern Pacific, it is from May 15 to November 30.

Case Studies
Galveston Hurricane
Hurricane Camille
Hurricane Hugo
Hurricane Andrew
Hurricane Floyd
Typhoon Toraji

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