Unit 11 Hurricane!

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Hurricane force

　　Hurricanes develop over ocean water that is at or above a temperature of 80°F (27°C ) .A hurricane is composed of bands of thunder - storms and cumulus that spiral around the storm center, the calm, cloud - free eye, which is typically 20 - 25 miles (30-40 kilometers) across. In the cloud wall around the eye exceptional wind speeds occur: the smaller the eye, the higher the wind speeds. Hum-canes vary greatly in their intensity, and in meteorological terms are classified according to their “damage potential” on a five- point scale, ranging from minimal (1) to catastrophic (5) . Such measurement is based on air pressure in a storm's eye, because the lower the pressure, the greater the wind speeds in the hurricane. A hurricane that measures 5 on the scale is characterized by air pressure below 920 millibars, producing wind speeds of over 155 miles an hour (250 km/h) and a coastal storm surge in the sea of over 18 feet (5. 5 meters) above the normal level. Fortunately, fewer than I percent of all hurricanes fall within this category.
　　One hurricane that did, however, was Hurricane Gilbert, which swept through the Gulf of Mexico in September 1988. As this hurricane, 950 miles (1, 500 kilometers) in diameter, passed over Jamaica, it generated as much energy as the country would need for the next 1, 000 years, at current later of consumption. Although Hurricane Gilbert traveled at a mere 10 - 15 miles an hour (18-25 km/h), the wind around the eye at the center, where air pressure was a record low of 885 millibars, reached speeds of over 200 miles an hour (320 km/h) .
　　A tidal surge of 20 feet, flash floods from torrential rainfall that totalled 10 - 15 inches (250 - 380 millimeters) in a few hours, and the creation of 24 tornadoes as the storm reached land, all together contributed to the devastation caused; 318 people lost their lives, 100, 000 people were evacuated from the Mexican coast, and 500, 000 people were rendered homeless in Jamaica.
　　Forecasting the power and path of a hurricane remains problematical although satellite monitoring since the 1970s has allowed far more of a warning to be given to those in the path than was once the case.

How Hurricane Is Formed

　　In the second half of each year, many powerful storms are born in the tropical (热带的) Atlantic and Caribbean seas. Of these, only about half a dozen become the strong, circling winds of 75 miles per hour or more that are called hurricanes, and several usually make their way to the coast. There they cause millions of dollars of damage, and bring death to large numbers of people.
The great storm that hit the coast start as soft circling wind hundred—even thousands—of miles out to sea. As they travel aimlessly over water warmed by the summer sun, they are carried westward by the southeast winds. When conditions are just right, warm, moist(潮湿)air flows in at the bottom of such a wind, moves upward through it and comes out at the top. In the process, the moisture in this warm air produces rain, and with it the heat is changed to energy in the form of strong winds. As the heat increase the young hurricane begins to move in a counter-clockwise motion(逆时针运动).
　　The life of a hurricane is only about nine days, but it contains almost more power than we can imagine. The energy in the heat released(释放)by a hurricane’s rainfall in a single day would satisfy the entire electrical needs of the United States for more than six months. Water, not wind, is the main source of death and destruction(毁灭)in a hurricane. A typical hurricane brings 6 to 12 inch downpours, causing sudden floods. Worst of all is the powerful movement of the sea—the mountains of water moving toward the hurricane center. The water level rises as much as 15 feet above normal as it moves toward shore

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