Forecast calls for 9 hurricanes

ARNOLD MARKOWITZ
Herald Staff Writer

It could be out there already or two months away: Arlene, the first Atlantic tropical storm of 1999, a little whirl of wind lurking in a tropical wave promenading between Africa and North America.

Three such waves -- waves of air, not water -- were out there Wednesday. There will be opportunities for hurricane development in many more to come, in the six-month season that begins Tuesday.

On the other hand, Arlene may pop out of a low pressure center that forms in the southwest Caribbean Sea near Central America, or in the Gulf of Mexico near Yucatan. This early in the season those are better bets than a tropical wave, but nothing might happen soon.

Technically, hurricane season here in the Atlantic Basin begins Tuesday and ends at midnight on Nov. 30, and while there are no certainties, here is a forecast: 14 tropical storms, the same number as last year, Arlene through Nate. Nine will become hurricanes, one fewer than last year. Four of those will be classified as intense, one more than last year, with top wind speed 111 mph or worse.

That comes from atmospheric scientist William M. Gray of Colorado State University. Gray forecasts the season as a whole, not individual storms. He can't say which ones will hit land, or where, or which ones will be intense, but he's fairly sure these things will happen:

``The 1999 season should have hurricane activity comparable to the recent busy seasons of 1996 and 1998. Evidence suggests we have entered a new era of enhanced major hurricane activity.''

That bad? Ask Jerry Jarrell, director of the National Hurricane Center.

``I think so,'' he answers. This year, Jarrell has a full staff of six forecasters who specialize in hurricanes, plus himself and his deputy, Max Mayfield, who are able to take a turn on the forecast desk. It looks like they'll be needed.

If Gray is right or nearly right about the amount of hurricane activity, he says, there is a statistically high probability of intense hurricanes making landfall on the Gulf Coast between the Texas-Mexico border and Pasco County, Fla.-- the county just north of St. Petersburg. There is an even higher probability of such a landfall from Pasco down the Gulf Coast and up the Atlantic side as far as Maine.

But where? Gray cannot say.

``The probability of a landfall in any one place is very low,'' he said. It is not the sort of statement that inspires standing ovations.

Gray expects a lot of this year's hurricanes to start in African tropical waves, producing long-track storms that begin in low latitudes around 10 degrees, south of the Cape Verde Islands off Senegal.

``It means that you'll typically have longer-lived and more intense storms,'' he said Wednesday. ``The really intense blockbusters mostly are low latitude-forming storms. It means that maybe Florida's a little bit more under the gun, because your main threat is these west-by-northwest moving storms that go just north of Puerto Rico and track into southern Florida.''

Gray and his research group follow 13 atmospheric ``climate predictors'' that tend to determine how active the next hurricane season will be. They do a lot of hind-casting, applying their data to prior seasons to make sure that what they think works really does.

This year, they have found the predictors greatly similar to those of three long-ago hurricane seasons -- 1950, 1955 and 1961. On average, those seasons produced 12 tropical storms instead of the long-term average of 10. There were 9.3 hurricanes instead of the average six, and six intense hurricanes instead of the average 2.8. 1950 was the worst of those years -- 13 storms, 11 of them hurricanes, seven of the hurricanes intense, and all squeezed into August, September and October.

``It doesn't mean for sure that we're going to follow those years, but the probabilities are pretty good,'' Gray said.

The most familiar of the climate predictors he uses is the cycle of extra-warm (El Niņo) and extra-cool (La Niņa) sea surface temperatures on the Pacific Ocean, along the equator.

Two years ago El Niņo caused strong high-altitude winds that sheared the upper air circulation off incipient hurricanes, so the 1997 season was a welcome washout.

Then the Pacific cooled off quickly, effectively popping the lock and letting out a parcel of storms in '98.

This year the Pacific is cooler -- as much as 2 degrees Celsius below normal on Wednesday. That is cool enough to qualify as a La Niņa event. The last one happened in 1995, when there were 11 hurricanes. Opal, Roxanne and Marilyn were the worst.

High-altitude winds blowing west to east are crucial, too. When they are strong, which doesn't require an El Niņo event, they inhibit hurricane development. When weak, they are boosters. Gray is positive that will happen this year.

Another pro-hurricane factor is sea surface temperature on the Atlantic. It's on the warm side. A warm surface supplies a hurricane with heat energy, like dry wood tossed on a fire under a chimney.

Those factors also are major influences favoring formation of hurricanes in the low latitudes close to Africa. Fed into tropical waves, they make trouble.

In any given six-month hurricane season, you can bet there will be at least 100 tropical waves. On average, 10 or 15 percent turn into something -- a tropical depression, wind speed 30-35 mph, and then a tropical storm, 39 mph. If atmospheric conditions are right -- warm sea surface temperatures at the bottom, no strong crosswinds at the top -- the wind speed keeps increasing. At 74 mph, it's a hurricane. Some storms take several days to go through the process. Some do it in a few hours.

In some ways, the procession of tropical waves is predictable as rush hour on I-95. Something bad seems sure to happen, but when and where?

If you're lucky, Arlene runs out of gas and stops on the shoulder. Bret turns off at the next exit. Cindy comes close enough to splash you, then swerves away.