After between 8"-9" fell last night in the hardest hit areas, near Katy, resulting in widespread street flooding, we could face a similar setup tonight. The location will be slightly different, but pictures on tomorrow morning's news could be much the same: brown flood waters and stalled cars.
The latest data suggests we'll most likely see areas southeast of Houston most soaked. This will favor Chambers and Liberty Counties, but if the weather system responsible drifts a bit farther west (which it could do), inland Galveston County and Chambers County, plus Brazoria (City of Pearland) and eastern Harris Counties, could get drenched.
UPDATE: Flooding possible tonight southeast of Houston. This is where latest data places heaviest AM commute rain. pic.twitter.com/vyebQqyEpx— Brooks Garner (@BrooksKHOU) August 8, 2017
A stalled low is the force causing this trouble. After more afternoon heating from sunny breaks and tons of deep, tropical moisture enveloping the region, we could face hourly rainfall rates of over 2" per hour where the rain bands develop. It could rain in the same areas for hours on end, resulting in over 7"+ of rain in a few spots.
The best advice I can offer if you're out late tonight, is to with extra caution. Many will be heading to work at the refineries east of downtown, where some of the heaviest rain could fall. The most likely onset is after midnight, and it could continue through the morning commute. Remember, at night it's harder to tell the difference between a puddle and a flood zone so assume the worst if you see reflections on the street.
There were almost, 'comical' moments early today when monster trucks were required to rescue stalled vehicles, but for the folks who got stuck facing thousands of dollars in car repairs, it's no laughing matter.
So what's driving this low pressure? It's called a, "Meso-Convective Vortex" (MCV). This is a system which is most active at night because of how it works. It's like a heat engine, sucking-in surrounding moisture to its core, making it stronger. It's similar to how a tropical cyclone works. In this case, cooler air outside of the warm-core low is naturally attracted to the lower pressures inside the comparatively sultry center. Moisture blows-in from all sides toward the center, combining for heavy rain.
It's a good thing that this system is forecast to remain over land because if it were to drift into the waters of the Gulf of Mexico, we could quickly witness a tropical storm form. For now we'll only see isolated flooding rain, which might resemble a tropical system.
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