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Forecasters: 15 to 21 named storms expected for Atlantic hurricane season

Collage depicts hurricane storm surge, NOAA National Hurricane

Collage depicts hurricane storm surge, NOAA National Hurricane Center Director Ken Graham presenting a forecast, evacuation route sign, and Hurricane Hunter pilot flying into a storm. Credit: NOAA

Don’t be fooled by the recent lull in hurricanes and other powerful storms sweeping up from the Gulf Coast.

Scientists said Wednesday that even more storms strong enough to be named now are expected. That raises the possible range to from 15 to 21 from the earlier forecast in May of from 13 to 20.

The National Oceanic and Atmospheric Administration's new estimate for the Atlantic hurricane season includes the five storms seen so far.

One of them, Hurricane Elsa, which dwindled to a tropical storm when it struck Florida on July 2 before drenching much of the East Coast, was the earliest to race through the alphabet to the letter E.

"After a record-setting start, the Atlantic 2021 hurricane season does not show any signs of relenting as it enters the peak months ahead," Rick Spinrad, NOAA administrator, said in a statement.

There is a 70% probability for from seven to 10 hurricanes, with three to five of them becoming major hurricanes, Matthew Rosencrans, lead seasonal hurricane forecaster at NOAA’s Climate Prediction Center, told reporters on a conference call.

That means they would qualify as: A Category 3, with wind hitting at least 111 mph; a Category 4, with minimum winds of 130 mph; or the most powerful Category 5, when winds reach at least 157 mph.

NOAA previously forecast one less hurricane, with a range of from six to 10.

Both estimates reveal just how unusually active this June 1 to Nov. 30 season might become. From 1991 to 2020, the average has been only three major hurricanes, seven weaker Category 1 and 2 hurricanes, with minimum winds of 74 mph and 96 mph, respectively, and 14 named storms, NOAA says.

The recent break in the storm cycle since Elsa, experts say, partly occurred because in mid-July a large volume of dry air and dust blew across the Atlantic from the Sahara Desert, which tends to starve storms of the moisture they need.

Yet some of the same forces that made last year so exceptionally perilous — with 14 hurricanes — again are evident, according to Rosencrans.

For starters, NOAA says, there is the "backdrop of the ongoing warm phase of the Atlantic Multi-Decadal Oscillation, which has been favoring more active hurricane seasons since 1995."

This long-term pattern of warming and cooling temperatures on the surface of the North Atlantic can have widespread effects, NOAA says. Higher temperatures make it more likely tropical storms will turn severe; lower temperatures can cause Midwest droughts, including the Dust Bowl of the 1930s.

This year, there again is the possible return of La Niña, which occurs when the equator’s east-to-west trade winds intensify, pushing the Pacific Ocean toward Asia. That allows the sea’s coldest layers to rise to the surface off the west coast of South America.

The jet stream then veers north, toward the U.S. West Coast, clearing a path for more hurricanes, though experts say they tend to sweep up from the South to the Ohio Valley and the Great Lakes, instead of along the East Coast.

While a stronger La Niña may spell below-average snowfall for the mid-Atlantic region, NOAA says, it may lengthen the storm season.

"Extending the season is possible, especially if we get a La Niña," Rosencrans said.

However, hurricanes draw strength from warm water, and Rosencrans said the Atlantic’s temperature at the surface should be a bit cooler than last year. Recently, he said, the temperature was just slightly below normal by about 0.1 degree Centigrade. That works out to around 0.18 degrees Fahrenheit.

And yet, at least two other factors — "reduced vertical wind shear and an enhanced West Africa monsoon all contribute to the current conditions that can increase seasonal hurricane activity," he said.

Wind shear, a sudden change in the direction or speed, can impede or prevent hurricanes from forming; tropical waves, which can be thought of as clusters of thunderstorms, can sweep west from Africa, spawning Atlantic storms, experts say.

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