Future Hurricanes May Pack More Punch

The names will be different, but more hurricanes with the powerful punches of Hugo and Gilbert may be prowling the Atlantic, Caribbean and Gulf of Mexico in the future.

“The probability of more intense hurricanes in the Atlantic region is greater in the next decade or two than it has been in the 1970s and ‘80s,” says meteorologist William M. Gray of Colorado State University, who analyzes hurricane patterns.

Gray predicts a possible return of the more ferocious hurricanes of the ‘50s and ‘60s, because of an apparent break in the periodic West African drought. Rainfall in the Sahel, typically associated with more intense hurricane activity, was above average in 1988 for the first time since 1969, he says. A second rainy summer this year indicates an end to the drought.

The most intense hurricanes, Gray explains, usually form at low latitudes from tropical disturbances moving westward from Africa. The well-watered conditions in the ‘50s and ‘60s produced 31 of the most severe kind (categories 4 and 5) in the 17-year period 1950 to 1967.

Hurricanes are classified by the Saffir-Simpson scale, the fiercest a No. 5, or catastrophic storm. The atmospheric pressure at its center drops drastically and its wind speed exceeds 155 m.p.h.

In the drier 17-year period of 1970 to 1987, there were only 13 severe storms. In the ’88 and ’89 seasons--June through November--there have been five.

Last year’s Gilbert, which left a wide swath of devastation across Jamaica and the Mexican Yucatan, was the mightiest hurricane on record in the Western Hemisphere. Its atmospheric pressure dropped to 885 millibars and its wind speed reached 200 m.p.h.

This September’s Hugo, which ripped through the Virgin Islands and Puerto Rico before clobbering South Carolina, had sustained winds of 150 m.p.h. and an atmospheric pressure of 918 millibars (27.1 inches). Officially a 4 on the Saffir-Simpson scale, it “may be a borderline 5,” says meteorologist Mark Zimmer of the National Hurricane Center in Miami.

The strongest recorded storm on Earth, Zimmer says, was 1979 Typhoon Tip in the western Pacific, with a low pressure of 870 millibars. Outside the Atlantic area and the eastern Pacific, hurricanes are called typhoons or cyclones.

Fortunately, most Atlantic-region hurricanes do not develop to their worst potential. In this century, only two No. 5 hurricanes have struck the United States with full force, the 1935 Labor Day storm that ravaged the Florida Keys and 1969’s Camille, which slammed ashore at Mississippi and Louisiana. In 1980, Allen, the mightiest Caribbean storm then recorded, had lost much of its punch before it hit the Gulf Coast of Texas.

“If the future is like the past with its pattern of atmospheric conditions, there is a good probability of the return of stronger storms,” Gray said.

But in the 1990s, he warns, U.S. destruction will be at least four to five times more costly than in the ‘50s and ‘60s, because of the boom in population and property development along coastal areas.

The threat of global warming also portends hurricanes more powerful than any yet recorded, says meteorologist Kerry Emanuel of the Massachusetts Institute of Technology.

Hurricanes are like huge, self-sustaining heat engines spinning across the sea. They get their power from the water’s warmth. To develop, they need tropical ocean-surface temperatures of about 80 degrees Fahrenheit.

“If tropical ocean temperatures go up, the intensity of hurricanes will,” Emanuel explains. “Sea-surface temperatures set the upper limits.”

The biggest uncertainty, he says, is whether global warming will affect tropical ocean temperatures.

The gradual warming of the Earth results from the greenhouse effect, caused primarily by the accumulation of carbon dioxide and methane in the atmosphere, which, like the glass of a greenhouse, trap heat.