In the hottest months of each year, many powerful storms are born in the Atlantic and Caribbean seas. Of these, only about half a dozen cause the strong, circ ling winds of 75 miles per hour or more that are named hurricanes, and several usually make their way to the coast. There they cause millions of dollars of damage, and most seriously, bring death to large numbers of people.
The great storms that hit the coast start as harmless circling disturbances (大气搅动)hundreds, even thousands, of miles out at sea. As they travel aimlessly over water warmed by the summer sun, they are carried westward by the trade winds. When conditions are just right, warm, wet air flows in at the bottom of such a disturbance, moves upward through it and comes out at the top. In this course, the wetness in this warm air produces rains, and with it the heat is changed into energy in the form of strong winds. As the heat increases, the young hurricane begins to swirl (旋转) in a counter-clockwise (逆时针) motion.
The average life of a hurricane is only about nine days but it contains almost more power than we can imagine. The hidden energy of the heat given off by a hurricane's rainfall in a single day would satisfy the entire electrical needs of the US for more than six months. Water, not wind, is the main source of death and destruction in a hurricane. A typical hurricane brings 6-to-12-inch downpour resulting in sudden floods. Worst of all is the powerful movement of the sea, the mountain s of water moving toward the low-pressure hurricane center. The water level rises as much as 15 feet above normal as it moves towards shore.
