It's already raining in southeastern Texas and there's more where it came from. The latest forecast from the Weather Prediction Center shows 5-10" of rain—with higher totals possible in spots—falling over the next couple of days. Forecasters painted a bullseye of 10"+ across a significant stretch of real estate between Corpus Christi and Houston. Not everyone in the 10" zone (or 7", or 5"...) will see 10" (or 7", or 5"...) of rain, but it's certainly possible where thunderstorms begin training, or repeatedly moving over the same areas.
The WPC's flash flood forecast has parts of coastal Texas under a moderate risk for flash flooding on Tuesday and Wednesday. The threat for flooding exists, but the fact that the rain will be steady over a few days rather than falling all in one horrendous downpour should lessen the risk to an extent. The threat for street flooding and natural waterways rising out of their banks will exist where heavy, persistent rains fall, especially in a short period of time. Flooding is flooding whether it's widespread or localized, and it's dangerous no matter what.
Why will the rain stick around in Texas without moving? You can thank the heat that'll roast the eastern part of the country for the next few days.
You usually don't have to worry about heavy rain or thunderstorms during a heat wave—the very pattern that allows it to get so hot is also stifling thunderstorm development. However, you often run into those problems on the outer periphery of heat waves. The high pressure in a heat wave acts like a dome that shunts active weather around it. This is why severe thunderstorms tend to move north toward the Canadian border around this time of the year. The ridge is also why tropical disturbances can stall out when they affect the southern United States.
Heat waves are products of stagnation, both at the surface and in the upper levels of the atmosphere. The lack of movement allows a tropical disturbance like the one enveloping eastern Texas this week to just sit there and rain for several days. There's nothing to move it along. The rain will come to an end once the ridge—and with it, the stagnation—breaks on Wednesday and Thursday.
The possibility of heavy rain in Texas this week has been advertised for more than a week thanks in large part to hair-on-fire social media pages that talked about a strong hurricane smacking into the Gulf Coast this week. Some weather models kept trying to turn the disorganized disturbance into a strong storm; spinning up phantom hurricanes is not an uncommon flaw in certain weather models (*cough* the GFS *cough*).
As a result of that irresponsible hype-mongering on social media, Texas meteorologists worth their weight have had to spend much of the past 10 days trying to calm down people whose anxiety is through the roof. Storm anxiety is a big issue in Texas as we're less than a year removed from the record-breaking devastation of Hurricane Harvey. The category four hurricane made landfall near Corpus Christi, Texas, in August 2017, and its remnants meandered over the Houston area for more than a week. The storm dropped two to three feet of rain and led to widespread flooding that dwarfed the inundation caused by Tropical Storm Allison in 2001.
Thankfully, this won't be like any of those record-breaking storms that come to mind when we think of tropical rainfall in Texas. If you stay alert for warnings and stay aware of your surroundings this week, you should be okay.
[Model Animation: Tropical Tidbits | Map: Dennis Mersereau]
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