HURRICANES Responding to timely warnings holds the key to tempering their impact
AMERICANS who endured Hurricane Gloria, Hurricane Juan, or prepared for Hurricane Nele in the Pacific might spare a thought for Beniot Vies. The Cuban Roman Catholic priest organized one of the first hurricane warning services a century ago. Hundreds of observers around the Cuban coastline kept a weather eye out for ominous sea swells or streaming cirrus clouds that foretold a storm. When danger threatened, the observers sent warnings by pony express.Skip to next paragraph
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With today's high-techology surveillance, no hurricane sneaks in undetected. Even the uncertain forecasts of Gloria's track represent a quantum leap in alertness beyond the pony riders. Yet for recipients of the warnings, the message forecasters want to get across is the same as that of Vies -- it is better to prepare for a potential threat that fails to materialize than to act as though there were no threat at all.
National Weather Service (NWS) meteorologist James I. Campbell makes no apology for the Gloria forecasts. He calls the many watches and warnings ``timely for this storm.''
Neil Frank, director of the National Oceanographic and Atmospheric Administration's National Hurricane Center in Miami, repeatedly stresses the inherent uncertainty in hurricane forecasts. The NOAA center found errors for the period 1970-79 of 434 miles, 281 miles, and 125 miles respectively in its 72, 48, and 24 hour forecasts of hurricane tracks. Dr. Frank says he does not ``expect a major improvement in the next decade.'' Under these circumstances, overwarning is part of the price of hurricane safety .
Meteorologists such as Frank urge people not to let what may seem to be false alarms make them complacent. Decades of research have given atmospheric scientists a healthy respect for a hurricane's power. Named for Huracan
Named for Huracan, an ancient Central American evil deity, hurricanes are a product of atmosphere and ocean. They develop amid torrential thunderstorms spawned by disturbances over warm tropical seas. Water vapor, flowing in from distant regions, feeds their growth and drives their fury. For most storms, the strongest sustained winds blow at about 112 miles per hour. Yet sustained winds of nearly 200 m.p.h. have been recorded; gusts have peaked as high as 224 m.p.h. Hurricanes have earned their ti tle of the fiercest storms on Earth.
Although the role they play in the atmosphere's general circulation remains obscure, decades of research have shown that hurricanes strongly influence their regional environment. Low-level winds spiraling toward the storm from distances of several hundred to a thousand miles or more move in such a way that air throughout the troposphere -- the layer of atmosphere that ranges from the earth's surface to between 10,000 and 20,000 feet in altitude -- slowly sinks. This subsidence suppresses cloud formation
so that unusually clear skies in the normally cloud studded tropics often signal the approaching storm.
However, within about 250 miles of the storm center, inflowing air begins to converge strongly. Tropospheric air begins to lift and the towering convective cumulus clouds, which form the main body of the storm appear. This transition between clear skies and storm clouds -- the so-called ``bar'' of the storm -- can be sharp, although high-level winds may carry a veil of cirrus clouds well beyond it. Indeed, the appearance of cirrus together with unusual ocean swell is another sign of a hurricane's approa ch. Columbus read this portent during his fourth voyage (1502-04) and warned the governor of Hispanola of the danger. But the governor ignored the forecast, sent his treasure fleet to sea, and lost it.
Wind speeds pick up as the spiraling air nears the storm center. While still approximately 10 to 60 miles out, the air flow turns sharply upward in the ring of massive cumulus clouds called the eye wall. Here is where the heaviest rains fall and the strongest winds blow. Inside that wall lies the calm of the hurricane eye. Sea level air pressure here is 5 to 10 percent or more lower than it is outside the storm. The sea surface domes up. This mound of water, which moves with the storm, adds to water hea ped up by the powerful winds to create the storm surge that sweeps ashore like a monstrous tide when a hurricane makes landfall. Atmospheric powerhouse
A mature hurricane is an atmospheric powerhouse. Typically, the vigorous circulation -- in at the bottom, up through the clouds, out at the top -- moves about 2 million metric tons of air per second to heights of 40,000 to 60,000 feet. The power required to lift air at that rate is several hundred times the 675,000 megawatts of installed electrical generating capacity of the United States. Additional power to maintain the horizontal winds is puny by comparison -- about 15 megawatts, on average, wh ich is the capacity of a moderate-size power plant.