SCIENCE IN THE NEWS - Storms of September: One Month, Three Hurricanes in the Atlantic

This is SCIENCE IN THE NEWS in VOA Special English. I'm Bob Doughty.
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And I'm Barbara Klein. Our subject today: severe ocean storms.
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September is usually the worst month for hurricanes in the Atlantic Ocean. At least ten named storms have formed there this year. The hurricane season continues until the end of November.
The total number of major storms this year has been above average. There were three major hurricanes in the Atlantic Ocean. The latest hurricane to strike land was called Hurricane Ike. It was a huge storm, stretching out across a thousand kilometers when it struck the southern coast of the United States last month.
Hurricane Ike caused major flooding and destroyed thousands of homes. It also left millions of people without power in Texas. The storm killed at least thirty people in nine states.

The situation was even worse in the nation of Haiti, which has been severely damaged by several storms this year.

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About ninety ocean storms form each year around the world. These powerful storms are called hurricanes when they form in the Atlantic Ocean and the eastern Pacific Ocean. They are called typhoons in the northwestern Pacific, and cyclones when they develop in the Indian Ocean. Severe ocean storms in the northern half of the world generally develop in late summer or early autumn near the equator.
Storms can result when the air temperature in one area is different from that of another. Warmer air rises and cooler air falls. These movements create a difference in the pressure of the atmosphere. If the pressure changes over a large area, winds start to blow in a huge circle. High-pressure air is pulled toward a low-pressure center.

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Severe ocean storms happen less often in the southern hemisphere. There, the season of greatest activity is between December and March. South of the equator, the winds flow in the same direction as the hands on a clock. North of the equator, they flow in the opposite direction.
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Storms can get stronger as they move over warm ocean waters. The strongest, fastest winds of a hurricane are found in the eyewall. This is the area that surrounds the center, or eye, of the storm. The eye itself is calm by comparison, with light winds and clear skies.
Wind speeds in severe ocean storms can reach more than two hundred fifty kilometers an hour. Up to fifty centimeters of rain can fall. Some storms have produced more than one hundred fifty centimeters of rain.
These storms also cause high waves and ocean surges. A surge is a continuous movement of water that may reach six meters or more. The water strikes low coastal areas. Surges are commonly responsible for about ninety percent of all deaths from ocean storms.
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Scientists use computer programs to show where a storm might go. The programs combine information such as temperatures, wind speed, atmospheric pressure and the amount of water in the atmosphere.
Scientists collect the information with satellites, weather balloons and devices floating in the world's oceans. They also collect information from ships and passenger flights and from airplanes that fly in and around storms. The crews drop instruments on parachutes to record temperature, pressure, wind speed and other conditions.
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The Saffir-Simpson Hurricane Scale is a way to rate storms based on wind speed. It provides an idea of the amount of coastal flooding and property damage that might be expected.
The scale is divided into five groups. A category one storm has winds of about one hundred twenty to one hundred fifty kilometers an hour. It can damage trees and lightweight structures. It can also cause flooding.
Wind speeds in a category two hurricane can reach close to one hundred eighty kilometers an hour. These storms are often powerful enough to break windows or blow a protective covering off a house. Winds between about one hundred eighty and two hundred fifty kilometers an hour represent categories three and four. Anything even more powerful is a category five hurricane.

To be continued