National Geographic : 2000 Oct
IN HURRICANE ALLEY HOW STRONG WILL THE WINDS GET? COMPUTERSIMULATION:ISAACGINIS, UNIVERSITY OFRHODEISLAND Sea-surface temperature ('F) 78 80 TA hurricane affects its own intensity . . by interacting with the ocean," says e 1Isaac Ginis, an oceanographer at the University of Rhode Island. This is how it happens: Warm water at the top of the ocean fuels a hurricane. As it spins, the hurricane churns the water beneath it, bringing cooler water up from the depths (right). The cooler the water that it brings up, the less fuel the hurri cane has. In the Caribbean, where even the deep water is warm (far right), hurricanes tend to be more powerful. In the Gulf of . Mexico (above), where the warm layers of water are shallower, "hurricanes essentially kill themselves," explains Ginis. In September 1988 Hurricane Gilbert illus trated that difference, reaching wind speeds of more than 175 miles an hour early on but weakening once it moved across the YucatBn Peninsula into the Gulf. Traditional predictions of hurricane intensity have been based primarily on changes in the atmosphere. Taking into account subsurface sea temperatures, Ginis created a model that improved intensity forecasts by 30 percent last year. "The U.S . spends $700,000 a mile to prepare a coastal area during a hurricane warning," he says. "A more skillful fore cast will reduce the size of the area on alert, so we're talking about big potential savings." ONE DAY, SIX TEMPESTS All at once, on August 23, 1995, tropi cal storm Karen, Hurricanes Humberto and Iris, a tropical wave, and tropical storm Jerry (right to left) whirl across the Atlantic Ocean and the Caribbean Sea; tropical storm Gil spins in the Pacific. That year's Atlantic hurricane season, from June to November, and the four following ones were the busiest ever recorded.