Metro

This is why Harvey stuck around Houston

AFP PHOTO / NOAA-NASA GOES PROJECT

For Harvey, what a long, strange trip it’s been — and that has meant misery for Texas residents who are enduring deadly, catastrophic flooding.

Why did the epic storm, which made landfall Friday as a hurricane in Texas, slow down and linger? And why did it head back out into the Gulf of Mexico, where it is now poised to sweep ashore again early Wednesday up the Gulf Coast in southwestern Louisiana?

Meteorologists say it was the result of a war in the atmosphere that stalled a system that was only doing what all tropical storms want to do — distribute heat and moisture from the tropics to the north.

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What normally steers Atlantic tropical cyclones (a term that includes tropical depressions, tropical storms, and hurricanes) is a big ridge of high pressure called the Bermuda High, located over the Atlantic Ocean, said Bob Smerbeck, senior meteorologist at Accuweather.com. The high pressure meanders back and forth, east and west across the Atlantic.

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The flow around the high pressure system is clockwise, and the storms swing around the edge.

At the same time, there is another high pressure system typically situated over the western United States and Mexico, Smerbeck said.

He said Harvey had been “riding around the rim of the Atlantic high” when the high over the western United States strengthened and began to push the storm back southeastward.

Harvey “couldn’t go any further, so it just meandered,” he said. “That’s the worst thing that could happen is that it slows and stalls. That was the worst-case scenario for Houston and all of southeastern Texas.

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“That was the biggest problem with Harvey. You had a fight going on between those steering highs. The western US high won the fight right after Harvey made landfall and stopped Harvey in its tracks.”

Such storms “want to go north . . . they all eventually do,” said Joe D’Aleo, co-chief meteorologist at WeatherBell Analytics.

He said the weather models had showed early last week that the storm would head at a decent pace toward Texas but once there, the two high pressure systems would “connect and block the road to the north.”

Smerbeck said that the track of the storm wasn’t that unusual. “We’ve seen many tropical cyclones do loops. They’re very chaotic sometimes.”

Smerbeck said the high pressure to the west is now “breaking down and the eastern high is strengthening again,” which means Harvey will finally make its way through the eastern United States this weekend, leaving Texas and Louisiana to recover from the deluges.

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The storm brought record rains to Texas. The old record of 48 inches of rain from a tropical system set back in 1978 during Amelia was broken when a rain gauge over southeastern metro Houston exceeded 49 inches.

“This sort of extreme rainfall tests our ability to forecast extremes as well as society’s ability to endure them,” said Dave Epstein, a meteorologist for Boston.com and WBUR-FM.

How soon will the rain stop in those devastated areas?

Smerbeck said heavy rain will continue around the Houston area and that part of Texas into Wednesday, but the heaviest rains may let up in Houston by Tuesday night as the storm shifts toward Louisiana.

D’Aleo said most of the rain will be over by Wednesday evening in the Galveston and Houston areas, but he noted that the end of the rain doesn’t mean the end of the crisis, as rivers can continue to rise.

He warned that such storms can develop quickly, noting that just eight days ago, the country’s attention was completely focused on the solar eclipse, while Harvey was just a harmless “mass of clouds” in the ocean off the Yucatan Peninsula.