HURRICANE ONSLAUGHT

By BY J. MADELEINE NASH CHICAGO

ALLISON. BARRY. CHANTAL. DEAN. Erin. Felix. Gabrielle. Humberto. Iris. Jerry. Karen. Luis. If residents of low-lying coastal areas are anxious this summer, they have a dozen reasons--and more are undoubtedly on the way. The hurricane season has not yet peaked, but menacing storms are already rumbling across the Atlantic Ocean one after another, like warplanes taking off from a carrier deck. Last week alone, four ominously swirling air masses zigzagged across satellite weather maps, packed so close together that it almost seemed they might merge to form a single monster storm. "You feel like you're standing in the line of fire," says Debby Sandberg, a high school math teacher in Miami. "You just keep waiting for something to hit."

No one under retirement age can recall a hurricane season quite like this. Not since 1933, says Bob Burpee, director of the National Hurricane Center near Miami, have so many hurricanes formed so early in the year. So far, 12 tropical storms have materialized off the west coast of Africa, six of which have grown into full-fledged hurricanes. The good news is that the damage to date--floods in the Carolinas, toppled trees and power lines in Central Florida, mud slides on the Caribbean island of Martinique--has been comparatively mild. The bad news is that more big storms are on their way, and before the end of November, when the season officially ends, one or two may yet slam into land with savage power.

But even if that doesn't happen, an ominous question remains: What, if anything, does this unnerving spate of extreme weather signify? Is it just a meteorological fluke, a one-season anomaly? Or could it signal a potentially devastating long-term trend? Atmospheric scientist William Gray of Colorado State University fears the answer is the latter.

Indeed, he notes, the large number of storms this year seems unusual only because the U.S. has experienced a hurricane lull for the past 25 years. A correction is now overdue and, when it comes, he warns, "We're going to see hurricane damage like we've never seen it before." It's not that the storms are necessarily getting more severe but that there has been massive population growth and an accompanying building boom along the Atlantic and Gulf coasts. More people live between Miami and Fort Lauderdale, notes political scientist Roger Pielke Jr. of the National Center for Atmospheric Research, than occupied the entire coastline from Texas to Virginia 60 years ago.

While boom-and-bust hurricane cycles lasting decades have been well documented, the reasons for them remain obscure. That's not the case for individual storms, though. Atlantic hurricanes inevitably get their start in Africa, where hot, dry air overlying the Sahara desert collides with cooler, moister air over the sub-Saharan region known as the Sahel. Under normal conditions, the collision produces eddies of low-pressure air that drift out over the ocean, where storm clouds begin to form. Most of the time, the clouds simply dump their load of rain and dissipate.

But every so often, one of these low-pressure systems, its winds spinning slowly counterclockwise, starts to strengthen-and that's when the trouble can begin. During late summer and fall, broad swaths of subtropical ocean can reach temperatures of 80o/F or more. The warm, humid air above the ocean surface would tend to rise anyway, and when a low-pressure region drifts by, it's like taking the lid off a steaming pot. The air rushes upward, dumping its moisture and energy, which forces the winds to whirl ever faster. Meanwhile, down at the surface, more warm air rushes in to replace what's risen, and it shoots upward in turn. After a few days of this self-sustaining process, a low-pressure tropical depression can escalate into a tropical storm and then, if the winds reach a sustained 75 m.p.h. or more, a full-blown hurricane.

That's the textbook version at least. In practice, nature often kills hurricanes before they are born. For example, the intermittent warm-water current in the Pacific Ocean known as El NiCURo generates westerly winds that reach halfway around the globe to disrupt cloud formations that might otherwise form hurricanes. In fact, says Colorado State's Gray, a major reason there have been so few hurricanes in recent years is that El Nino has continued on a more or less nonstop basis.

The terrible, two-decade drought that plagued the African Sahel until lately also cut down on tropical storms, says Gray. Strong winds that accompanied this prolonged dry spell swept rain clouds away from the Sahel and sheared the tops off storm systems that might eventually have become hurricanes. Now that the drought has eased, these storms are more likely to persist and grow.

OTHER FACTORS-VARIATIONS IN ocean temperatures and in high-altitude prevailing winds-are also involved. Nobody can say with any certainty why these me teorological influences come and go as they do. Gray favors a mechanism known as the Great Ocean Conveyor Belt, a vast, and so far poorly understood, undersea current that carries warm water from the Pacific and Indian oceans into the Atlantic. When the conveyor belt runs faster for unknown reasons, there is more warm water available to generate both rain in the Sahel and storms over the North Atlantic. Or so the reasoning goes.

But even though nobody has a handle on the underlying dynamics, the link between far-flung weather patterns and the North American hurricane season appears solid. Indeed, for the past 12 years, Gray has routinely used El Nino, Sahel rainfall and other factors to make impressively accurate predictions. Last October he forecast 12 major tropical storms for 1995, and in early August he upped the number to 16, just five storms shy of the record set in 1933 and more than double the number in 1994. "People thought we'd gone crazy," says Gray. "Now it appears we probably undershot."

So far, there's absolutely no evidence that this year's upswing in storms can be attributed to that always fashionable suspect global warming. It's logical to assume that warmer oceans will give rise to more dangerous hurricanes. But the warming, if it's real, is still too small to have much effect. That doesn't mean it won't happen in the future, though. Hurricanes might not be more frequent in a hotter world, but they could be more intense. The upper limit on wind velocities should increase, M.I.T. atmospheric scientist Kerry Eman uel calculates, perhaps as much as 40 m.p.h. over their current top speed of about 180. And while major urban centers won't be battered by winds at the top of the range any more than they are today, there would be a rise in potential danger.

While the threat from global warming is purely theoretical, the danger from an old-fashioned, decades-long spate of stormy seasons is real. Gray says we need look back only to the 1950s and '60s, when 21 hurricanes pummeled the U.S., to see what could lie ahead for coastal residents. Those hurricanes took hundreds of lives in the U.S. and thousands in the Caribbean. While lives can be protected by early warning and prompt evacuation, protecting property is another matter. If Hurricane Andrew had veered just 20 miles farther north on its destructive path through South Florida in 1992, it might have done $100 billion in damage rather than $25 billion.

Earthquakes may get more press, but hurricanes can be far more destructive. "They are," Gray says, "the biggest natural threat facing the U.S." Nobody can predict whether a given storm will blast through a city or dissipate harmlessly at sea. But it doesn't take an atmospheric scientist to realize that the more storms there are, the greater the danger of disaster.

--With reporting by David Bjerklie/New York

With reporting by David Bjerklie/New York