The outlook for hurricanes this year? Quieter than normal, says one forecaster
For hurricane-prone areas bordering the Atlantic, there's hope for a quieter storm season this year. Hurricane forecaster William M. Gray of Colorado State University, who hit last year's storm season on the nose, says that some of the factors that go into his forecast suggest that there will be fewer than normal important tropical storms and hurricanes this summer and fall.
Professor Gray warns that it's too early to make more than an educated guess at this year's activity. So he says he's giving an ``outlook,'' not a ``forecast.'' But that's more than any meteorologist could do a few years ago.
Gray says the most important upshot of his research so far is the identification of three factors that significantly affect the frequency of North Atlantic hurricanes. These include:
El Nio, a condition that brings major shifts of atmospheric pressure patterns and rainfall over the tropical Pacific Ocean. Gray notes that El Nio brings strong westerly winds at about 40,000 feet over the hurricane area. These so inhibit a storm's growth that when they are present there's only about 30 percent as much hurricane activity as in a normal year.
The Quasi-Biennial Oscillation (QBO), a curious wind shift in the lower tropical stratosphere. These winds cycle between westerlies and easterlies every 16 to 20 months or so. Gray finds there's nearly twice as much hurricane activity with strongly westerly QBO winds than when the winds blow from the east.
Shifts in the average sea-level pressure in the Gulf of Mexico and Caribbean Basin. For reasons no one understands, tiny differences are influential.
Even though he doesn't fully understand the influence of these factors, knowing about them helps explain why one season has more hurricanes than another. It's in developing this after-the-fact understanding where Gray says ``the three factors . . . hold up very well.'' Trying to use them to predict what a season will be like in advance is just icing on the cake.
Last year, there was no El Nio. QBO winds were from the west. Sea-level pressure was closer to its long-term average. Gray and his team correctly forecast 7 hurricanes -- only one above normal.
Gray says he has no idea whether he can repeat that forecast success. His guess that 1986 may be a light hurricane year reflects his expectation that QBO winds will be from the east and that a new El Nio is moderately likely to develop.
However, he cautions that, light season or not, people in hurricane-vulnerable areas can't afford to let down their guard. ``Even though there's a fewer number of storms,'' Gray says, ``you may have one storm that comes right over you; and that may be a very active year for you.''