...essure in the center of the funnel, hich causes structures to explode hen they are not sufficiently ventilated to adjust rapidly to the pressure difference. The pressure reduction is in keeping ith Bernoullis principle, hich states that pressure is reduced as velocity increases.Tornadoes are most common and strongest in temperate latitudes, and in the U.S. they tend to form most frequently in the early spring the tornado season shifts toard later months ith increasing latitude. The number of funnels observed each year could vary greatly in any given region.Cyclone, in strict meteorological terminology, an area of lo atmospheric pressure surrounded by a ind system bloing, in the northern hemisphere, in a counterclockise direction. A corresponding high-pressure area ith clockise inds is knon as an anticyclone. In the southern hemisphere these ind directions are reversed. Cyclones are commonly called los and anticyclones highs. The term cyclone has often been more loosely applied to a storm and disturbance attending such pressure systems, particularly the violent tropical hurricane and the typhoon, hich center on areas of unusually lo pressure.Hurricane, name applied to migratory tropical cyclones that originate over oceans in certain regions near the equator, and particularly to those arising in the est Indian region, including the Caribbean Sea and the Gulf of Mexico. Hurricane-type cyclones in the estern Pacific are knon as typhoons.Most hurricanes originate ithin the doldrums, a narro equatorial belt characterized by intermittent calms, light variable breezes, and frequent squalls, and lying beteen the northeast and southeast trade inds. As the doldrums of the Atlantic are situated largely to the north of the equator, hurricanes do not occur in the South Atlantic Ocean. The Pacific doldrums extend north and south of the equator thus hurricanes occur in the South and North Pacific oceans.Hurricanes consist of high-velocity inds bloing circularly around a lo-pressure center, knon as the eye of the storm. The lo-pressure center develops hen the arm, saturated air prevalent in the doldrums is forced upard by denser, cooler air. From the edge of the storm toard its center, the atmospheric pressure drops sharply and the ind velocity rises. The inds attain maximum force close to the point of loest pressure about 724 torr, or about 28.5 in. of mercury. The diameter of the area affected by inds of destructive force may exceed 240 km 150 mi. Gale inds prevail over a larger area, averaging 480 km 300 mi in diameter. The strength of a hurricane is rated from 1 to 5. The mildest, Category 1, has inds of at least 120 kmh 74 mph. The strongest and rarest, Category 5, has inds that exceed 250 kmh 155 mph. ithin the eye of the storm, hich averages 24 km 15 mi in diameter, the inds stop and the clouds lift, but the seas remain very violent.Hurricanes generally move in a path resembling the curve of a parabola. In the northern hemisphere the storms usually travel first in a northesterly direction and in the higher latitudes turn toard the northeast. In the southern hemisphere the usual path of the hurricane is initially to the southest and subsequently to the southeast. Hurricanes travel at varying rates. In the loer latitudes the rate ranges from 8 to 32 kmh 5 to 20 mph and in the higher latitudes it may increase to as much as 80 kmh 50 mph. Those areas in hich the hurricane inds blo in the same direction as the general movement of the storm are subjected to the maximum destructive violence of the hurricane.Since 1943 U.S. military aircraft have been flying into hurricanes to measure ind velocities and directions, the location and size of the eye, the pressures ithin the storms, and their thermal structure. A coordinated system of tracking hurricanes as developed in the mid-1950s, and periodic improvements have been made over the years. Radar, sea-based recording devices, geosynchronous eather satellites since 1966, and other devices no supply data to the National Hurricane Center in Florida, hich follos each storm virtually from the beginning. Improved systems of prediction and communication have been able to help minimize loss of life in hurricanes, but property damage is still heavy, especially in coastal regions. The strongest hurricane to hit the estern hemisphere in the 20th century, Gilbert, devastated Jamaica and parts of Mexico in 1988 ith inds that gusted up to 350 kmh 218 mph. Destructive hurricanes in recent U.S. history include Agnes 1972, ith 3 billion in damage and 134 deaths, Hugo 1989, ith more than 4 billion in damage and more than 50 deaths, and Andre 1992, ith an estimated 12 billion in damage, more than 50 dead, and thousands left homeless.Page PAGE 2 NUMPAGES 2-5YZcs 0JmHnHu0Jaj0JUaCJaJCJ6BCJsaJphBCJaJph5BCJt
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