A 2018 study found tropical cyclone speed has decreased globally by 10% since 1949 as atmosphere warms, which creates chance for drenching rain to inundate coastlines
By Jennifer Hiller and Devika Krishna Kumar
HOUSTON/MOBILE, Ala., Sept 16 (Reuters) - For Grant Saltz, who runs a barbecue restaurant in Mobile, Alabama, what struck him about Hurricane Sally was its steady, deliberate pace, after the storm rumbled into the U.S. Gulf Coast on Wednesday as a powerful Category 2 hurricane.
"It's so slow, this one," said Saltz, 38, while clearing away tree branches during a pause in the rains. "We had strong winds for a long period of time. Instead of a few hours, we got it for 12 hours."
Sally is not the most powerful storm to batter the U.S. Gulf Coast in recent memory, but its glacial pace is becoming a regular feature of the deadly storms, which many scientists attribute to climate change. The storm has already dropped more than 18 inches (46 cm) of rain in the last 24 hours, with more rainfall looming, the National Hurricane Center said.
At one point during its approach, Sally was moving at a mere 2 miles per hour (3.2 km per hour), recalling Hurricanes Harvey in Houston in 2017, Florence in the Carolinas in 2018, and Dorian in the Bahamas in 2019, massive weather systems that parked over land and dumped rain that had to be measured in feet instead of inches.
A 2018 study found that tropical cyclone speed has decreased globally by 10% since 1949 as the atmosphere warms, which increases the chance that drenching rain inundates the coastline, said Jennifer Collins, professor in the school of geosciences at the University of South Florida.
"These North Atlantic hurricanes are increasingly likely to stall near the coast for many hours," Collins said.
The connection to climate change is not settled, but there is evidence that a warming Arctic weakens the winds that can help move a hurricane along its track or push it into the Atlantic away from land, said Jim Kossin, climate scientist with the National Oceanic and Atmospheric Administration who authored the 2018 paper and others on the topic.
The result can be a storm like Sally "that tracks into a stagnant area and there's no steering flow and it just sits there," Kossin said.
The slow storms worry scientists given how busy 2020's hurricane season has been. The Atlantic basin has seen eight hurricanes already, a milestone reached at this point just three times in the past - in 1893, 2005 and 2012, said Phil Klotzbach, atmospheric scientist at Colorado State University.
The National Hurricane Center is monitoring four storms now - Sally, Paulette, Teddy and Vicky, with another system in the southwestern Gulf of Mexico possibly becoming a depression in the next several days.
The popular focus on the Saffir-Simpson Hurricane Wind Scale, which ranks hurricanes on a 1 to 5 rating based on sustained wind speed, "doesn't take into account the storm surge and the rainfall flooding," Collins said, which is usually more deadly than high winds.
Questions about storms and climate change first emerged 15 years ago during Katrina in New Orleans, and people were "extremely cagey about those answers," said Kim Cobb, climate scientist with Georgia Tech.
Hurricane Harvey overwhelmed the city of Houston with rain for several days and turned highways into tidal rivers as the wettest ever tropical cyclone to hit the United States. Sally has not been as bad, but the extent of the rain still surprised residents.
"No one expected it to be this bad," said Cody Phillips, who manages De Soto's Seafood Kitchen in Gulf Shores, Alabama, and a lifetime Alabama resident. "It's because it stalled. If it had just passed through, we would've been fine."
(Reporting by Jennifer Hiller and Devika Krishna Kumar; Editing by David Gaffen, Tom Brown and Lisa Shumaker)
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