Saharan dust cloud over the Atlantic [image credit: NASA]
For the first time in seven years, no hurricane has formed in the Atlantic Basin by mid-August. An excess of Saharan dust is thought to be a factor.
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After two years of alphabet-exhausting tropical storms, and the disruptive remnants that have soaked the Philly region, the 2022 Atlantic hurricane season is off to a surprisingly benign start, says The Philadelphia Inquirer.
And it may have something to do with all the heat the Philly region and much of the East endured July into August.
All those ominous outlooks notwithstanding, for the first time in seven years, no hurricane has formed in the Atlantic Ocean, Caribbean Sea, or the Gulf of Mexico by Aug. 15. The long-term average for a first hurricane, one with peak winds of at least 74 mph, is Aug. 11.
So far only three named storms — those with qualifying winds of at least 39 mph — have developed, and none since Colin fizzled back on July 3.
“It sure has been quiet the past few weeks in the Atlantic,” said Philip Klotzbach, a Colorado State University hurricane specialist who was among those calling for quite an active season. He still is, but in his update issued Aug. 4, he bumped down his numbers slightly.
On the same day that National Oceanic and Atmospheric Administration forecasters at the Climate Prediction Center also subtly — very subtly, as in magnifying-glass level — downgraded their outlooks.
However, be apprised that the climatological peak of the season doesn’t arrive until Sept. 10, and forecasters are confident that even if this one doesn’t match the output of the destructive 2020 and 2021 seasons, it still will have ended up being quite a busy one.
In the meantime, here is what hurricane experts say is behind the late start.
Saharan dust
Klotzbach and AccuWeather’s Jonathan Porter cite the dust coming off the Sahara Desert as a factor.
This so-called ultra-dry Saharan Air Layer, or SAL, an annual occurrence, has been occupying the air in the hurricane-spawning grounds, and it is quite an effective tropical storm repellent, according to Jason Dunion, SAL researcher with the University of Miami’s Rosenstiel School and other specialists.
Disturbances along the southern Sahara lift massive amounts of dust that can be 2-miles thick or more as it travels across the Atlantic from late June to mid-August, he says. That can put the kibosh on would-be tropical storms.
“Interestingly, the U.S. East Coast has seen quite a bit more Saharan dust than usual, especially from mid-July to early August,” Dunion said. That may have something to do with the area of high pressure over the Atlantic that baked the East with heat. “But for now, I’d call it a mystery that we’ll need to dig into.”
“SAL certainly has helped keep things calm,” Klotzbach said last week.. “We can see a fair amount of dry air across the tropical Atlantic.”
Cooler Atlantic
Sea-surface temperatures in the “main development region” have been below long-term averages at times during the last two months, say the climate center specialists.
Warm water is a critical fuel source for hurricanes.
In addition, says Klotzbach, the temperature contrasts have been favorable for stirring up shearing winds that can keep a storm from developing.
Wind shear
Hurricanes form and grow when warm, moist air over the ocean rises. Strong upper-level shearing winds can put a cap on the ascending air, stifling a storm’s growth.
“We’ve had some decent pulses of stronger-than-normal shear over the past two months,” Klotzbach said, although not “crazy strong.”
And conditions in the tropical Pacific, where sea-surface temperatures are below normal, or in La Niña, argue for an uptick in hurricane activity.
Full article here.
via Tallbloke’s Talkshop
August 18, 2022 at 06:09AM
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