Andrew May Have Been the Storm After the Lull
HURRICANE Andrew's devastating attack on Florida last August may have been a just foretaste of future dangers.
It was a major storm - a category 4 on a scale that ranges from 1 (mildest) to 5 (most severe). It is rare for such a powerful storm to come ashore in the experience of most people now living in Caribbean, Gulf of Mexico, and North American Atlantic seaboard regions. But such events may not be so rare in the future, according to hurricane scientist William Gray of Colorado State University at Fort Collins.
Dr. Gray predicts that the hurricane season that began June 1 "should overall be about an average season." It should have about seven hurricanes, including two storms of category 3, 4, or 5 intensity. Last year, he correctly forecast four hurricanes, including one major storm - Andrew.
This continues a long-playing pattern of relatively restrained hurricane action. But Gray warns that what he calls the "great lull in ... [category 3-4-5] landfalling hurricanes over the past 25 years" can't be expected to continue indefinitely. On the basis of historical and geological records, he expects a return to a pattern of more major hurricanes. He adds that, because of coastal development, the United States could "see hurricane destruction as never before experienced."
Gray's warning reflects the fact that the more scientists study North Atlantic hurricanes, the more they learn of their destructive potential. For example, Gray bases his warning on more than the history of the storms themselves. He also takes account of the climatology of several factors that strongly influence a hurricane season's activity.
These include the presence or absence of an El Nino warm-water pool in the equatorial Pacific Ocean. A warm El Nino inhibits Atlantic hurricane formation. Winds that girdle the planet at heights of 16 to 35 kilometers (52,500 to 115,000 feet) also play a role. They reverse direction roughly every two years. On average, there's almost twice as much Atlantic hurricane activity when the winds tend to blow from the west than when they blow from the east. The Colorado researchers have also found several regio nal factors - such as West African rainfall and air pressure patterns - that influence hurricanes.
Gray sees the "lull" in major hurricane attack as a "natural consequence" of a slowdown in Atlantic Ocean circulation. This is closely related to such factors as West African drought and increased El Nino activity over the past 25 years. When this pattern changes, hurricane action may pick up.
Scientists also are finding new aspects of storm violence. For example, University of Chicago meteorologist T. Theodore Fujita found evidence of small rotating vortexes in pictures of Andrew's destruction. These are different from the tornadoes that hurricanes often spawn. They form in the eye wall where winds spiral around the hurricane's quiet center. They can spin up to speeds of perhaps 80 miles per hour (m.p.h.). When pushed along by the hurricane's main winds, the combination of the speed with whic h the vortex travels over the ground and its spin speed can produce a total wind of 200 m.p.h. or more.
Although an encounter with one of these vortexes would be rare, it could demolish a structure in seconds. Buildings designed to withstand expected sustained hurricane winds would be vulnerable to this previously unexpected hazard.
If the frequency of landfalls by major hurricanes picks up, the damage potential is far higher than is generally realized. Insurance companies, safety officials, and residents in vulnerable areas should wake up to this fact. Their current plans for coping with hurricane disaster are likely to be quite inadequate.