| Date: Sun 03-Jul-1994 Paper Page: 2 Publication: Sunday Sun, Supplement Writer: Q: HOW DO hurricanes start? A: A hurricane starts in either of two ways: As a tropical wave -- not a sea wave but a wave of tropical air -- from the coast of West Africa; or a tropical depression. Some tropical depressions form in the Caribbean Sea, the Gulf of Mexico or the Atlantic when the right conditions -- among them low pressure and isolated thunderstorms -- come together. On average, there are ten tropical depressions in a hurricane season. Q: Do all tropical depressions become hurricanes? A: No, but in an average season six of them do. Q: What is a tropical storm? A: That's what a tropical depression becomes if the circulating wind blows steadily at 40 mph and an eye forms -- a roundish patch of calm air around which the wind circulates. When that happens, the storm is given a name. Q: Who gives them names, and why? A: Hurricanes are named to make it easier to keep track of them. Weather forecasters in the countries affected by hurricanes suggest names to the World Meteorological Organisation, which has a committee that picks an alphabetical list of 21 names (no Q, U, X, Y or Z) each hurricane season (June 1-November 30). Hurricanes have been given names since 1950. At first, forecasters used the military names for letters of the alphabet -- Able, Baker, Charlie, and so on. Later women's names were used, and still later men's and women's names were used alternately. In recent years, Spanish and French names have been used along with English ones because these are the languages spoken in hurricane-affected areas. Q: How does a tropical storm become a hurricane? A: It speeds up. If wind speed around the eyes hits 74 mph, a hurricane is born. Q: How strong can hurricanes become? A: Hurricanes are measured on a scale -- the Saffir-Simpson Scale -- of one to five, depending on their maximum sustained wind speed. A Category One storm has winds of 74 to 95 mph; a Category Five storm, 155 mph or greater. Q: Which is worse, a tornado or a hurricane? A: A hurricane -- by a long shot. While winds in the strongest tornado can top 300 mph, a tornado is much smaller and more short-lived than the smallest hurricane. A mile-wide tornado is huge, but a 100-mile wide hurricane is small. Typically, tornadoes last less than an hour, while a hurricane can go on for days. Q: What's the eye of a hurricane like? A: The inside of the eye is calm and clear, like a chimney, through which air rises, heated by the ocean. This (heat) gives the storm the energy it needs to intensify; warm ocean waters are the fuel that keeps a hurricane churning. The size of the eye fluctuates from 10 to 15 miles across, with the strongest wind whirling around it in a belt about 50 miles wide. Beyond that, reaching out as far as 200 miles, gale-force winds circulate. As a hurricane grows, squalls of rain and wind break off the edges and move further ahead. Q: How fast does a hurricane move? A: Forward speed varies and fluctuates; 10 to 15 mph is typical. Q: What determines where it goes? A: A hurricane's path is dictated by what's going on in the atmosphere around it. In Hurricane Andrew's case, September 1992, a huge ridge of high pressure over the eastern United States blocked it from moving up the Atlantic coast, as hurricanes tend to do when winds blow across the United States from the west. Instead, it moved along the southern boundary of the high-pressure system on a course to South Florida and on to the Gulf of Mexico. As the storm made its way into the Gulf, it moved along a path between the western boundary of the high-pressure system and the eastern edge of a big low-pressure system over the western United States before it hit the Louisiana coast. Q: How does a hurricane die? A: Because a hurricane is fueled by warm water, it starts falling apart when it comes over cold water or, in the case of Andrew, over land. But even though it's no longer a hurricane, it can still dump a lot of rain and create a lot of havoc. |