Residents near and along the Texas coast, particularly in Houston, are feeling worried about a new risk for flooding following the catastrophic flooding that occurred last summer to due Hurricane Harvey. Some towns received over 50 inches of rain from that storm. To be clear, this new disturbance will be nothing like Harvey, and their respective strengths should not even be compared. First of all, the region will not be at risk for a tropical cyclone. Earlier this week, the National Hurricane Center designated an area of disturbed weather as Invest 91L. As of Friday morning, the hurricane center indicated that tropical development is not expected. Instead, a trough, or elongated area of low pressure, will move into eastern Mexico and southern Texas, carrying a deep plume of tropical moisture with it. This plume may bring record moisture to some parts of Texas and Louisiana this weekend as heavy rain threatens the region for the day.
Solely heavy rain and localized flooding will be the main risks associated with this area of disturbed weather. On Friday, other than a few spotty showers along the Texas coastline, the region will be dry throughout the day and into the overnight hours. The moisture plume will wait until Sunday to deliver the heavy rain. Thus on Saturday it will be another similar day, with only a few spotty showers possible near the coast.
It’s not until Sunday when the chance for rain ramps up, just in time for Father’s Day. Sunday will not be a washout, but coastal areas and locations a bit farther inland may experience rounds of rain and thunderstorms, especially during the latter half of the day. Not only will parts of Texas experience this rain, but portions of Louisiana will likely experience some rain as well.
Monday will likely be the biggest day in terms of heavy rainfall. This is due to the deepest tropical moisture moving onshore. In some locations along the Texas coast, precipitable water values may exceed 3 inches. This indicates an extremely moist atmosphere, with all signs pointing towards some very heavy rain. Rounds of rain and thunderstorms are likely across much of Louisiana and into southern and eastern Texas.
We’ll begin to see changes occur on Tuesday, however, as the trough of low pressure stalls over northeastern Mexico. Over the Southeast, high pressure will nudge further into Louisiana and Texas. This high pressure will lower the risk for rain across Louisiana and eastern Texas, although a few thunderstorms will still be possible. Meanwhile across southern Texas, the heavy rain may takeover. Parts of this region are in a severe and extreme drought so rain is needed, but if too much falls then flooding can occur.
By Wednesday, an isolated thunderstorm or two will be possible across the Gulf Coast, but otherwise the region and surrounding areas will be dry thanks to the high pressure. Across the Rio Grande Valley, however, another day of heavy rains will threaten the region.
It’s not until either Thursday or Friday when this disturbance finally falls apart and the risk for heavy rain is gone. Until this, scattered showers and thunderstorms will likely persist through next week in the Rio Grande Valley.
The rainfall forecast through Thursday night is still uncertain. We know coastal areas can expect a widespread 1 to 3 inches of rain and that localized areas will receive over 6 inches, but it’s uncertain where that best chance for the heaviest of rain will occur. Therefore, our rainfall forecast below is subject to change. The European model features of big bullseye of 4-8+ inches of rain in southern Texas, while the American model features a more broad area of heavy rain but with lighter totals downwards of 2-4 inches.