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Serious flood threat continues in Texas, Louisiana as more heavy rain brews

Some places have had nearly a foot and a half of precipitation

Water surrounds a house along flooded areas in Ascension Parish, La., on Tuesday. (Bill Feig/The Advocate/AP)

On Tuesday night, the nation’s fourth-largest city found itself under tornado, severe thunderstorm and flash flood warning simultaneously as dangerous thunderstorms and heavy rainfall moved through the greater Houston area. Some places across Texas and Louisiana have picked up more than 15 inches of rain since the start of the week in what has proved a deadly onslaught of high-impact flooding.

Flash flood emergencies were declared in Baton Rouge and Lake Charles, La., late Monday after a foot of rain came down, inundating streets and vehicles, seeping into homes and causing at least one fatality. Equally severe flooding snarled Fannett, Tex., east of Houston, where 17.16 inches of rain poured down to kick off the workweek.

Flash flood emergencies in Louisiana while double-digit rainfall deluges Texas

The deluges continued Tuesday, with 6.48 inches measured at Cedar Bayou in eastern Harris County, Tex., also to the east of Houston proper. Victoria, Tex., received 10.96 inches of rain Tuesday, prompting flash flood warnings. Heavy rains washed out parts of County Road 47 in Smith County, Tex., near Tyler.

Flash flood emergencies were declared in Baton Rouge and Lake Charles, La., on May 17. Volunteers faced floodwater as they attempted to secure a dam on May 21. (Video: The Washington Post, Photo: Rick Hickman/AP/The Washington Post)

The National Weather Service Weather Prediction Center has the entire Texas Gulf Coast and most of coastal Louisiana at a “moderate risk” of flash flooding and excessive rainfall, estimating that most areas have a 20 percent to 50 percent chance of flash flooding within 25 miles.

Flash flood watches remain in effect for all of eastern Texas, including Brownsville, San Antonio, Houston, Galveston and Waco and areas to east near the Golden Triangle, as well as for most of Louisiana, including Lake Charles, Baton Rouge and New Orleans. A widespread two to 3.5 inches of rain is expected Wednesday across coastal Texas, with one to 2.5 inches in Louisiana. Heavier amounts are possible locally.

Wednesday stands to be the wettest day of the next several over the most widespread area, and with more rainfall on the way Thursday, Houston could easily see an additional six inches or so. More bouts of rain, sometimes heavy, are likely to last into Saturday.

Wednesday’s forecast

On Wednesday morning, two clusters of thunderstorms were present in Texas, both of which will evolve and dominate forecasts and bring potential flooding. The first, located in South Texas between Corpus Christi and McAllen, was packing strong to damaging wind gusts and even had embedded circulations occasionally warranting tornado warnings.

To the east, radar was populated with bright oranges and reds as an enormous area of heavy rainfall stretched nearly 500 miles to the east over the Gulf of Mexico as warm, humid air rode north over a slowly sagging thunderstorm outflow boundary. That boundary, akin to a weak cold front exhaled by now-dead thunderstorms, was forcing air upward and transforming its moisture into prolific rainfall.

High-resolution weather models suggest that arcing batch of thunderstorms and extremely heavy rainfall will continue to plow almost due east, passing over the Gulf of Mexico and largely only clipping the coast as it tracks south of the Sabine River at the Louisiana-Texas border. That may actually be encouraging news and cut down on rainfall amounts farther inland from the immediate coastline, the storms usurping the greater instability, or energy for lift, and keeping the most favorable conditions for heavy rainfall offshore.

Uncertainty was high, though, because computer models were struggling to accurately resolve the ongoing storms.

“At this time, do not see a whole lot of model solutions getting the western parts of this activity correct, so not really sure how far north or northeast this will expand,” wrote the Weather Service in Houston.

Outlook for Thursday into the weekend

There are indications that the offshore trend of that rainfall could change Thursday, with bands of heavy rain stalling offshore of southwest Louisiana and expanding northward into an already hard-hit Lake Charles. That’s a place that, in addition to ongoing flooding, dealt with two direct hurricane strikes — including that of disastrous Category 4 Hurricane Laura — in 2020 and a damaging deep freeze and ice storm in February.

Extreme rain events in Texas, like the one this week, are becoming the new normal

Looking ahead, pockets of heavy rain will continue Thursday and Friday in East Texas and western Louisiana, with some indications of a break in the action by Saturday morning.

However, concern is growing that a renewed fire hose of moisture emanating from the Gulf of Mexico could be focused and enhanced by a nose of dry air from the northeast, rejuvenating heavy rain and storms late Saturday into Sunday. Confidence in this scenario is low, but any additional rainfall could prove problematic in an area where the ground is already saturated to the max. New Orleans, for instance, has picked up more than two feet of rain since the start of April.