Eric Berger

Moisture lined up in Gulf, will stream into upper Texas coast tonight

Moderate to heavy rains are falling tonight as moisture streams into Houston.  As Patricia’s remnants have moved across Mexico and into the western Gulf of Mexico this evening we have also seen increasing wind gusts, already over 30 mph in Galveston.

The big question, of course, is how much more rain the region will get tonight. Already, since about noon today, most of the Houston metro area has received 3 to 5 inches of rain. We’ve managed that OK, for the most part, because our very dry soils soaked that rain up, and rainfall rates weren’t exceptionally high — generally below 1 inch per hour.

But now the soils are soaked, bayous are beginning to rise, and the rain’s still coming. (Much of the metro area is presently under a flash flood watch.) I posted a similar image to the one below on social media earlier, and it highlights why meteorologists remain quite concerned about overnight rains.

(Intellicast)
(Intellicast)

 

There’s a lot going on here. The low pressure system off Brownsville is the remnants of Patricia, now back over the Gulf. It’s not expected to develop as it follows a trough of low pressure and moves up the coast. But to be a potent rainmaker it needn’t develop. As the system moves north-northeast it should help feed moisture (rain) into the upper Texas coast, including the Houston region.

At the same time the radar to the southwest of Houston — i.e. Corpus Christi — is dry. This is because dry air associated with a front is trying to move east, as well. This dry air will help to end rain showers tomorrow in Houston. But it could play some role tonight in weakening activity.

In the end my best guess is that we’ll see an additional 3 to 7 inches of rain over much of Harris and Fort Bend County, and coastal counties including Brazoria, Galveston and Chambers during the next 12 hours or so. If this rain comes all in a bunch, during a few hour period, it will overwhelm some bayous and exacerbate current high water problems on roadways.

White Oak Bayou in the Heights at about 10 p.m. (Jeff Lindner/HCFCD)
White Oak Bayou in the Heights at about 10 p.m. (Jeff Lindner/HCFCD)

 

It is going to be a close call tonight, and I will be up to track it. My next post will come around midnight or shortly after.

Posted at 10 p.m. CT

Houston bayous handling rains so far, still to be tested later

The first significant rains have moved into Houston this afternoon and early evening as 1 to 3 inches have generally fallen across the area during the last six hours.

Rain accumulations from 12:30 p.m. to 6:30 p.m. Saturday. (HCOEM)
Rain accumulations from 12:30 p.m. to 6:30 p.m. Saturday. (HCOEM)

 

Houston’s bayous have thus far handled the inflow of rain, no doubt aided by the fact that the region’s parched soils have sucked up some of the water and rainfall rates generally have been less than 1 inch an hour.

If the rains hold steady like this there will be few problems. But will they hold steady or increase in intensity? The answer is that, for some areas, tonight will bring mostly steady rains. But for other areas things will get much more intense.

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Heavier storms rotating into Houston, major flood event remains likely tonight


As expected, Houston today has so far only seen scattered light to moderate rain showers. However during the next few hours heavier storms are going to begin rotating into the region.

Radar snapshot at 3:45 p.m. shows somewhat stronger storms approaching Houston. (Intellicast)
Radar snapshot at 3:45 p.m. shows somewhat stronger storms approaching Houston. (Intellicast)

 

This won’t be the main event, but it’s going to soften up our soils for what should be considerably stronger storms later tonight.

Some of the latest forecast modeling continues to suggest the onset of this heavier rain, with rainfall rates of perhaps 3 inches an hour or higher, around 8 or 9 p.m. this evening. Such storms will have the potential to flood streets quickly.

Much of the latest modeling also indicates the very heaviest rains — locations where 10 or more inches might fall tonight — will come along the coast, from Matagorda to Galveston to Chambers and Jefferson counties. That doesn’t rule out inland counties, including Harris County, from such extremes, but that seems to be the way models are trending.

During the last few hours we have also seen favorable conditions for funnel cloud development, and most of the southern half of the Houston metro area is under a tornado watch until 10 p.m. tonight.

I’ll have a comprehensive update on the storms at 7 p.m. tonight.

Posted at 4:05 p.m. CT

Rains moving into Houston, flooding likely later tonight

Patricia has weakened into a tropical depression over central Mexico this afternoon, and it’s continuing to move north-northeast toward Texas. Although its circulation has diminished dramatically, its remnants will combine with an upper-level disturbance moving into Texas from the northwest, and also draw moisture from the Gulf of Mexico.

It looks something like this on the surface wind map:

Surface winds at noon. (earth.nullschool.net)
Surface winds at noon. (earth.nullschool.net)

 

This will lead to a substantial rain event for Texas, including the upper Texas coast. The principal threat remains heavy rain, and more specifically very intense hourly rain rates that exceed the capability of roads and bayous to carry the water away.

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