WITH the Atlantic hurricane season entering what is usually its most intensive period, it's good to know there should be fewer such storms than normal this year. In fact, tropical storm Arlene, which brushed Bermuda last week, was the first Atlantic disturbance of any kind strong enough to receive a name since the season opened June 1. That should please William M. Gray of Colorado State University. The only meteorologist to attempt a formal hurricane season forecast, he's calling for four hurricanes (two below the 40-year average), a total of seven hurricanes and tropical storms (three below average), and 15 hurricane days (10 below average) by the time the season ends Nov. 30. A tropical storm is called a hurricane when it has sustained winds of 74 miles an hour or greater. A hurricane day is any day during which a tropical storm exhibits such hurricane winds.
The preview is good news. But it comes with two important caveats.
Gray claims that his forecasting system accounts for half the year-to-year variation in Atlantic hurricane activity. Factors still unknown account for the rest of the variation. While the system was right on the money in predicting the number of hurricanes and tropical storms in 1985 and '86, it could underestimate those numbers this year.
Furthermore, the system can't predict when or where a storm will strike during the season. And, as Gray wryly notes: ``If there is only one Atlantic hurricane this year, but it happens to go over your house or business, then, of course, for you 1987 will seem to be a very active hurricane season,''
That's the bad news. Every year, the United States National Weather Service warns of potential disaster along the North American Eastern Seaboard and Gulf coast and some island areas where millions of people vacation or live in hard-to-evacuate areas. Because people have unwisely built where storm-driven water can wash them away, ``we are more vulnerable to hurricanes in the United States now than we have ever been in our history,'' the American Meteorological Society notes.
Thus, even though there may be few hurricanes this season, just one big storm sweeping across a vulnerable coastline could be disastrous. That is why the Weather Service continues to stress the importance of listening for and heeding hurricane warnings. But there are limits to what storm trackers can do in anticipating specific danger to specific areas. Often they cannot give more than 12 hours' warning to an area that would require 20 to 30 hours to evacuate. There is need for better land-use planning for future development and provision for quicker evacuation in areas that are vulnerable - even at the cost of building new causeways.
Gray bases his forecast scheme on several factors:
El Nino, a condition with unusually warm sea surface temperatures in the eastern half of the equatorial Pacific, which has global influence. Its presence this year should tend to suppress Atlantic hurricanes.
Quasi-biennial oscillation, a cyclical shift between easterly and westerly winds in the lower tropical stratosphere (60,000 to 110,000 feet) that, this year, favors hurricane suppression.
Small shifts in average sea-level air pressure in the Caribbean Basin-Gulf of Mexico area for the June to July period (not applicable in this year's forecast).
The strength of the west-to-east wind flow at about 40,000 feet over low latitudes of the Caribbean Sea (not applicable this year).
By identifying such factors as predictors of half the year-to-year variability in hurricane activity, Gray is beginning to gain new insight into what influences that activity. But there still is much to learn. In particular, he notes that Atlantic hurricane activity has been relatively mild since 1970 compared with earlier years. It could pick up again in the future, for reasons not yet known. This possibility adds to the urgency for dealing with the twin problems of wise land use and adequate evacuation planning for vulnerable North American coastal areas.
It seems incredible that people will protest poor evacuation plans for nuclear power plants, yet ignore the hurricane danger. Richard Wilson, chairman of Harvard University's physics department, suggests combining planning for evacuation from both natural and nuclear hazards wherever this is appropriate. Wilson, a nuclear safety expert, explains that quick evacuation of large numbers of people is needed in all cases. When plans for nuclear accident evacuation are integrated with plans for storm danger and other types of civil evacuation, then the plans will be exercised and will be known to work. It's a concept worth pursuing.
A Tuesday column. Robert C. Cowen is the Monitor's natural science editor.