Saturday, October 31, 2020

Tropical Storm Beta to bring heavy rainfall to coastal Texas, Louisiana as it crawls ashore early this week

Sep 20. 2020
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By The Washington Post · Matthew Cappucci, Andrew Freedman · NATIONAL, SCIENCE-ENVIRONMENT

Tropical Storm Beta is poised to bring torrential rainfall to stretches of the Gulf Coast in Texas and Louisiana, with heavy downpours and flooding possible to kick off the week. 

A half-foot or more of rain is likely in store for millions in the Lone Star State, with isolated double-digit totals possible near Houston and Galveston. Flash flood watches blanket the area as the slow-moving tropical storm nears.

"Flash, urban, and river flooding is likely," the National Hurricane Center warned Sunday morning. "The slow motion of Beta will produce a long duration rainfall event from the middle Texas coast to southern Louisiana." As the week goes on, heavy rains are forecast to spread into the Mississippi River Valley, prompting flood concerns there as well.

Wind and storm surge hazards are accompanying the system while Beta spins slowly towards landfall late Monday into Tuesday near Matagorda Bay, Texas, between Houston and Corpus Christi. 

Tropical storm warnings are in effect from Port Aransas, Texas, to Morgan City, La., as a 300-mile stretch of real estate is set to be lashed by Beta's waterlogged rain bands and expansive field of strong winds. 

Storm surge warnings are also in effect from Port Aransas to Rockefeller Wildlife Refuge, La., as the storm's large wind field pushes water onshore. Tropical storm-force winds extend out to 195 miles from the center of Beta.

Heavy rain was falling in southwest Louisiana early Sunday, drenching some of the same areas still recovering from Category 4 Hurricane Laura in late August. Tropical storm-force winds of greater than 39 mph were occurring along the Louisiana coast Sunday morning, and are expected to spread southwest along the Texas coast with time.

As of 11 a.m. Sunday, Beta had maximum sustained winds of 60 mph and was located about 180 miles southeast of Galveston. The storm was moving west-northwest at just 3 mph.

Beta is the second tropical or subtropical cyclone in 15 years to be named after a Greek letter, following behind Alpha, a rare subtropical storm that brought damaging winds to Portugal on Friday. This hurricane season has been spawning storms at a record pace, well ahead of the most active season on record, which occurred in 2005. 

Beta is located in an area of weak upper level winds, causing it to be slow-moving, which will exacerbate the flood threat. However, its poor organization and nearby dry air will help limit the flood potential.

The Hurricane Center indicates that while a few areas may see rainfall of up to 2o inches, primarily close to the coast in the vicinity of Galveston Bay, a more widespread swath from the middle Texas coast to southern Louisiana is likely to receive between 8 and 12 inches of rain.

However, it remains difficult to determine where the heaviest rain will fall. It appears that southwest Louisiana may see totals of one foot or greater, which is likely to cause flooding in already waterlogged areas hit hard by Laura. 

More than 30,000 are still without power in parts of coastal Louisiana from that storm, and many still lack access to fresh water.

In the Houston-Galveston corridor, bands of rainfall will probably pivot into the area by early Sunday afternoon, becoming moderate to heavy at times. Rainfall rates of an inch per hour or more are possible late in the day, with even heavier rainfall arriving during the overnight into Monday.

The Houston metro area is familiar with the risks of slow-moving tropical storms and hurricanes, having gone through Tropical Storm Alison in 2001, which caused at least $5 billion in damage, and Hurricane Harvey in 2017, which delivered the heaviest rainfall associated with a tropical storm or hurricane on record in the United States, at 60.58 inches. 

While Beta exhibits some similarities to those storms, such as its sluggish movement, the rainfall forecast does not look to be nearly as significant as those historic events. 

There may also be heavy rainfall in northwest Louisiana, southwest Arkansas or southern Oklahoma, which would be associated with the interaction between moisture streaming northward from the storm and a stalled frontal boundary. 

The greatest risk for this scenario to play out appears to be in south-central to southeastern Oklahoma, where a general 2 to 4 inches, with localized 6-inch amounts, is possible.

"(Beta's) remnants will be the predominant influence on our weather, generally keeping high chances (of rain) in the forecast for much of the upcoming work week," wrote the National Weather Service in Shreveport, La., which serves southeast Oklahoma.

In addition to heavy rainfall, a broad area of storm surge flooding is also likely along the immediate shoreline from coastal Louisiana to Texas. Storm surge refers to the storm-driven rise in water above normally dry land at the coast. 

A general 1- to 3-foot increase in water levels is likely along much of the Texas and western Louisiana coastline, with 2 to 4 feet between Aransas Bay in Texas and Lake Calcasieu in Louisiana, which includes Galveston Bay. Because the storm is crawling along, the surge will come during multiple high tide cycles, which will exacerbate beach erosion. Coastal flooding was already being reported in Galveston on Sunday morning.

Strong wind gusts, probably topping 60 mph in some areas, will also move ashore, particularly near Beta's center when it makes landfall overnight Monday into Tuesday.

Beta isn't the only tropical storm in the Atlantic right now. Hurricane Teddy will sideswipe Bermuda on Monday as a Category 1 hurricane, barely a week after Hurricane Paulette made landfall as a strong Category 1. Teddy will continue churning northwards, eventually transitioning into an extratropical cyclone and bringing strong winds to the Canadian Maritimes.

The remnants of Paulette, meanwhile, could attempt to redevelop in the coming days southeast of the Azores. (If it were to do so, it would not receive a new name for technical reasons.)

There is also Tropical Storm Wilfred, a struggling low-end tropical storm over the open tropical Atlantic that will probably weaken into a tropical storm depression by late Sunday. 



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