Discussion – 

0

Discussion – 

0

Significant Flash Flood Event Possible Overnight along the Upper Texas Coast & Houston Metro

The stage is set and we appear on the cusp of the play beginning. Heavy rainfall associated with the low-pressure area known as Imelda has fallen over the southern Houston Metro and Upper Texas coast this evening. Flash flooding has not occurred yet because of the recent dry weather. Most of the rain that has fallen thus far has been absorbed by soils. However, soils are approaching saturation and we anticipate run-off to increase substantially over the next few hours. As run-off increases and heavy rain continues we’ll start to experience more rapid rises on bayous and drainage systems. Roadways that typically flood or are low-lying will become dangerous to travel.

Simulated weather model radar for the overnight hours. Notice how heavy rain sets up along the Upper Texas Coast northward toward the Houston metro… and sits.

Advertisements

Short-term high-resolution weather model guidance is showing a rather ominous scenario overnight for south and eastern of the Houston metro. Evening weather balloon data confirmed the presence of a very moist airmass – as is typical with landfalling tropical systems. Also observed was a decent amount of atmospheric instability. That’s not being used to analyze severe weather potential tonight, but another way of saying that thunderstorms with extremely heavy rainfall are possible, if not likely at times. There will be a narrow corridor where the extremely high moisture values juxtapose with that more unstable airmass. That’ll generally occur near and east of the area of low pressure. With the area of low pressure moving over/near Houston later tonight, that’ll only enhance the concern of significant flash flooding over a large population center, especially across eastern Harris County south into Matagorda, Brazoria, Galveston, and Chambers counties.

For what it is worth – some of our weather model guidance are showing an additional three to six inches of rain falling along with parts of the Upper Texas Coast and Houston Metro by 4 AM. Isolated higher amounts (8-10 inches) cannot be ruled out. Keep in mind that at the time of this writing that those are rain totals for the next six hours. Where it has not yet rained it soils will be able to absorb initial rains. However, if those rains are falling at three to four inches per hour, even dry soils will not be able to handle it. On the opposite side of the spectrum – if we can keep the heavy rain ‘moving along’ and get some breaks in-between that would allow drainage systems to cope a bit better.

Tonight’s round of heavy rain may end up priming us for a more significant flooding threat tomorrow and tomorrow night when we see more heavy rain develop and fall on fully-saturated soils. Even if we get by tonight without many issues we still have to deal with several more rounds of heavy rainfall. 

Tags:

David Reimer

0 Comments

You May Also Like

Share to...