Wind Shear, Dry Air Curb Atlantic Storm Activity at Season Peak

By Brian K. Sullivan | September 10, 2015

The day during the Atlantic hurricane season when a tropical storm or worse is most likely to be swirling around the basin may come and go with a whimper.

The best the Atlantic probably will come up with by Thursday, the statistical peak of the season, is Tropical Depression Grace, which started out as a tropical storm on Saturday before wind shear and dry air took it down, according to the National Hurricane Center.

“It looks to be falling apart,” said Frank Strait, a senior meteorologist at AccuWeather Inc. in State College, Pennsylvania.

If Grace can’t get back up to storm strength by Thursday, and no other systems step up, this will be the second year in a row with neither a hurricane nor a tropical storm ranging across the Atlantic at the season’s six-month peak. Tropical depression 8, an unnamed system, started to form overnight about 220 miles east-southeast of Bermuda.

The dry air and shear that robbed Grace of power are also behind the lackluster showing of the mid-Atlantic at this usually very busy time of the year. They have kept many of this year’s storms from maintaining their top power for very long, said Matt Rogers, president of the Commodity Weather Group LLC in Bethesda, Maryland.

Biggest Culprit

The biggest culprit is shear, when winds blow at different speeds or directions at various altitudes.

“Nothing can survive,” said Phil Klotzbach, lead author of the Colorado State University seasonal hurricane forecast.

Across a large part of what’s known as the main development region, wind shear has been so strong that it has ripped storms apart. Even Tropical Storm Erika, which killed at least 20 on the Caribbean island of Dominica, was finally crushed by shear, a trek over land and dry air before reaching Florida as predicted.

“I don’t expect that to change,” Klotzbach said.

The strong El Nino in the equatorial Pacific Ocean actually helps keep wind shear in place over the Atlantic and it isn’t going anywhere anytime soon, according to forecasts from both U.S. and Australian meteorologists.

Normal Storm

If the system near Bermuda strengthens enough to get a name, it may be less of a tropical system and more of a normal mid-latitude storm, Strait said. It has the potential to bring some rain and winds to Canada’s Atlantic Provinces later in the week.

Further ahead, computer-forecast models have been toying with the idea of a storm in the Bay of Campeche at the western edge of the Gulf of Mexico early next week, Rogers said. A storm there would almost certainly spark interest among natural gas traders and energy companies working platforms and rigs in the Gulf.

While it’s worth watching, Klotzbach said he doesn’t think there’s any cause for panic. “It’s still a long way out,” he said. “Models spin up storms that don’t show up all the time.”

If the models still are keeping it alive through Wednesday, maybe “it could be something to watch,” Rogers added.

Or maybe it will be sheared apart like so many other storms this year.

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