Wait Till Next Time

Human memories are short, and even as the tattered ghost of Hurricane Floyd finally blew itself out over eastern Canada last weekend, it was easy to forget that it began the week as a meteorological giant--one of the century's largest and most powerful Atlantic storms. If it seems as if hurricanes are getting stronger these days, that's because they are. After a 30-year lull, the U.S. is once again being visited by hurricanes the size of the ones that battered the Eastern seaboard in the 1940s, '50s and '60s. Thanks to an unlucky confluence of events--warm Atlantic waters, brisk trade winds and some strange doings in the eastern Pacific--we're on the cusp of what could be an extended spell of very heavy weather.

Floyd is nothing, scientists warn, compared with what may lie ahead. In the next century, they say, we may see hurricanes that far exceed Floyd's top sustained winds and approach a hurricane's upper limit of 180 m.p.h.--more than capable of sending a 30-ft. wall of water surging inland, flattening houses, inundating coastal cities and stirring the ocean bottom to a depth of 600 ft.

Moreover, that 180-m.p.h. speed limit pertains only to present conditions. There's now a wild card in the climatic deck, observes M.I.T. atmospheric scientist Kerry Emanuel: global warming. Over coming decades, atmospheric pollution and the greenhouse effect are expected to heat not just the air but also the surface of the oceans, and it is the thermal energy of that water that fuels typhoons and hurricanes. As a rule of thumb, according to Emanuel, wind speeds increase 5 m.p.h. for every additional degree Fahrenheit of water temperature. By that formula, sustained winds in future hurricanes could conceivably top 200 m.p.h.

But even these storms, it should be noted, would look puny compared with the megastorm of unimaginable destructiveness that scientists have dubbed a "hypercane." Indeed, some meteorologists speculate that a runaway hypercane, triggered by the splashdown of a giant asteroid, may have been instrumental in wiping out the dinosaurs 65 million years ago.

What makes hurricanes? They are, in essence, just big wind machines that move heat from the equator to the poles. While they do this very efficiently, the same task could be performed by swarms of independent thunderstorms. It takes a certain amount of magic, in other words, to set a hurricane in motion. First, you have to make the thunderstorms, and then "you have to get the thunderstorms dancing," as Florida State University climatologist James O'Brien puts it. "You have to get them dancing in a big circle dance."

In Floyd's case, the dance started when a disturbance high in the atmosphere moved off the coast of Africa and out over the Atlantic. Fueled by the rise of warm, humid air (in places, sea surface temperatures measured a steamy 86[degrees]F), the disturbance very quickly spawned a brood of thunderstorms that coalesced in a slow-moving whorl known as a tropical depression. On Sept. 8, as its winds reached 40 m.p.h., Floyd became a tropical storm. On Sept. 10, when its winds topped 74 m.p.h., it became a Category 1 hurricane. A few days later, with winds approaching 155 m.p.h., Floyd very nearly became a Category 5 storm--the highest category of all.