Sally Crawls, Stalls Ashore

September 16, 2020

GOOD: Slow food, slow sex

BAD: Slow hurricanes

I asked the question last year after Dorian stalled over the Bahamas – is this slowing or stalling behavior becoming the new normal?

AP:

Hurricane Sally lumbered ashore near the Florida-Alabama line Wednesday with 105 mph (165) winds and rain measured in feet, not inches, swamping homes and trapping people in high water as it crept inland for what could be a long, slow and disastrous drenching across the Deep South.

Moving at an agonizing 3 mph, or about as fast as a person can walk, the storm made landfall at 4:45 a.m. near Gulf Shores, Alabama, after battering for hours a stretch of coastline that includes Mobile, Alabama, and Pensacola, Florida.

More than 2 feet of rain (61 centimeters) was recorded near Naval Air Station Pensacola, and nearly 3 feet (1 meter) of water covered streets in downtown Pensacola, the National Weather Service reported.MORE

“It’s not common that you start measuring rainfall in feet,” said National Weather Service forecaster David Eversole in Mobile, Alabama. “Sally’s moving so slowly, so it just keeps pounding and pounding and pounding the area with tropical rain and just powerful winds. It’s just a nightmare.”

More AP:

NAVARRE BEACH, Fla. (AP) — Heavy rain, pounding surf and flash floods hit parts of the Florida Panhandle and the Alabama coast on Tuesday as Hurricane Sally lumbered toward land at a painfully slow pace, threatening as much as 30 inches (76 centimeters) of rain and dangerous, historic flooding.

The storm’s center churned offshore 65 miles (105 kilometers) south-southeast of Mobile, Alabama, as Sally crept north-northeast toward an expected Wednesday landfall at 2 mph (3 kph), according to the National Hurricane Center. The forecast map showed the center likely coming ashore in Alabama, near the Florida line.

Hurricane force winds extended 40 miles (65 kilometers). Rain fell sideways and began covering roads in Pensacola, Florida, and Mobile. More than 80,000 power customers were without electricity, according to poweroutage.us .

Up to a foot (more than 30 centimeters) of rain had fallen already on the coast by Tuesday night and Sally’s lumbering pace meant there would likely be extended deluges. 

“A hurricane moving at 2 mph is stalled for all intents and purposes,” said Brian McNoldy, a hurricane researcher at the University of Miami. “If they aren’t moving along and they just kind of sit there, you’re going to get a ridiculous amount of rain.”

UPDATE: New York Times:

Other recent hurricanes have also stalled. A year ago, Dorian crawled over the Bahamas for a day and a half, causing widespread destruction from wind and storm surge. And Harvey, perhaps the best-known, and most costly, example of stalling, was no longer a hurricane by the time it stalled near Houston in August 2017. It had been downgraded to a tropical storm, but still it inundated the city and surrounding communities with four feet or more of rain over several days.

Hurricanes are carried along and steered by large-scale winds in the atmosphere, and research suggests that this atmospheric circulation is slowing down, at least at certain times of the year. Hurricanes could be affected.

A 2018 study found that globally since the middle of the 20th century, translation speeds of hurricanes and tropical storms had decreased by about 10 percent. Another study that year that focused on Atlantic hurricanes found that the average speed of storms near the North American coast had slowed by more than 15 percent.

This study also found a statistically significant trend in greater coastal rainfall and linked it to the increase in storms that stall. It said the results could be linked to natural climate variability and made no claims that human-caused climate change was at work.

But other recent research suggests that global warming — specifically in the Arctic, which is warming much more rapidly than other regions — is playing a role in weakening atmospheric circulation and thus potentially affecting hurricane speed.

Studies by Michael E. Mann, a climate scientist at Penn State, and others suggest that increased Arctic warmth reduces the temperature differential between that region and the tropics. This leads to a slowing of the jet stream, which affects other circulation patterns in the tropics but also in mid-latitude areas like North America.

“Our work indicates that climate change is favoring this phenomenon,” Dr. Mann wrote in an email message. “It likely plays a role in the decreased translation speed of landfalling hurricanes.”

Arctic warming is leading to other changes in the jet stream, Dr. Mann wrote, that are affecting weather to the south, including hurricanes. From spring through fall, he said, there is a greater tendency for large southward dips or other meanders in the jet stream to stay in place for days.

As they become stationary, these changes in the jet stream pattern lock zones of air in place, which can lead to prolonged heat waves or other extreme weather. Dr. Mann said that one such zone, of high-pressure air over the Central United States, favored the stalling of Harvey around Houston.

One Response to “Sally Crawls, Stalls Ashore”

  1. Gingerbaker Says:

    Sally Crawls, and Stalls Ashore…..

    Hal -ley-LOO- yah !


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