A large mass of storms continues to work through the Houston metro area this morning, but the rains have been manageable for the most part, with accumulations of 1-2 inches. However, we do have some significant concerns about areas to the southwest of Houston.
A particularly strong band of showers has established itself in Wharton and Fort Bend counties this morning. One location on the Colorado River, south of Wharton, briefly recorded rainfall rates in excess of 4 inches per hour, and has measured nearly 10 inches of rainfall since shortly before sunrise. A flash flood warning is in effect for this area through 9:45 a.m., and we anticipate these storms will slowly move east, toward Brazoria, southern Harris, and Galveston counties this morning. So if you live in the southern half of the metro area, pay close attention to the radar for the next several hours.
Area of flash flood warning in effect until 9:45am CT. (National Weather Service)
Most of the high-resolution modeling suggests this very moist air mass will shift mostly offshore by this afternoon, perhaps by around 2pm to 4pm. This should then lead to a reprieve in widespread storms at least through this evening.
The forecast for Thursday and Friday is not particularly clear, but we do not expect quite the organized storms that we are seeing across much of the Houston metro area this morning to persist. Nevertheless, heavy rain will remain a threat heading into the weekend. We will try to firm up this forecast in a new post later today.
We got through most of last night without any issues in Houston. Storms lined up well southwest of Houston near Matagorda Bay after midnight and have arrived across most of the metro area early this morning.
Radar at 5:40 AM shows widespread moderate to heavy rainfall across the Houston area. All this is moving slowly north and east and will be with us most of the morning. (RadarScope)
Radar as of 5:40 AM shows moderate to heavy rainfall across most of the area (with the exception of Freeport and north of The Woodlands). But everyone should see at least some rain through the morning.
As the day progresses, this rain will taper off or become more scattered in nature generally north and west of US-59/I-69. But heavy rain should continue into this afternoon generally south and east of there. A Flash Flood Watch remains hoisted for most of the area. We also have most areas south and east of US-59 in a “high risk” for flash flooding from the Weather Prediction Center today.
The Weather Prediction Center arm of NOAA has issued a “high” risk for flash flooding today for the southeast part of the area. (WPC/NOAA)
The WPC doesn’t hand out high risks easily, so that speaks to this system’s potential. A quick reminder from us: Please use caution when out and about today. It would be good to limit travel when you can on days like this, but if you are commuting or have to be heading out somewhere, be very careful and never drive through flooded roadways.
Total rainfall through this evening is expected to be on the order of 1 to 3 inches north and west of US-59. Some folks, particularly up in far northern regions (Conroe, Navasota, Cleveland to suggest a few) may see a bit less. The trouble spots are expected south and east of US-59. We expect 3 to 6 inches on average south and east of there, but some places will see higher amounts on the order of 6 to 10 inches or even a bit more.
Through this evening, rainfall amounts will average 1-3″ northwest of Houston and 3-6″ southeast of Houston, with higher amounts likely near the coast and bays. (NWS Houston via Weather Bell)
There are still some uncertainties with how this will exactly play out, but in general this will work for today as a forecast. This outcome would likely cause a good deal of street flooding in parts of southeast Harris, Galveston, Brazoria, and Chambers Counties. Bayou or creek flooding is also possible, especially along Clear Creek or perhaps some of the bayous in southeast Harris County.
The bottom line today: Flash flooding, particularly street flooding is likely in areas south and east of downtown Houston at times today, especially through early afternoon. Some more serious street or even creek and bayou flooding is also possible in a few places, depending on exactly how much rain falls and how quickly it does. Rain should taper off a bit, or at least become more infrequent toward mid-afternoon.
Storms that fired up on Tuesday afternoon have died down this evening, in part due to the loss of daytime heating. Unfortunately, this is just a lull, as the tropical disturbance that will make for wet conditions through Thursday morning remains in the Gulf, roughly centered near the border between Texas and Mexico. This pre-sunset satellite image captures the size of the tropical system, and amount of moisture it can potentially bring into Texas and Louisiana as it moves north-northeast. Fortunately, it appears the heaviest rains will probably remain offshore, but we’re still definitely in watch-and-wait mode.
Satellite image captured at 6:45pm CT Tuesday. (NOAA)
Our best tools to forecast rain totals over the next 24 to 36 hours, high-resolution models, have not done a tremendously good job so far today, and they’re not initializing well. This means that even 1 or 2 hours into an individual model’s run, it already is pretty far off what is actually happening on radar. So, to some extent, we’re flying blind in terms of forecasting.
Still, with high atmospheric moisture levels (precipitable water values will rise above 2.2 inches over the next day or so, which is a prerequisite for high hourly rainfall rates) and low pressure at the surface we’re all but guaranteed heavy rainfall for at least part the metro area. After the present lull, it appears as though rain showers will build back up sometime after midnight offshore, and begin to migrate inland again. It’s quite possible that Wednesday morning’s commute will be a soggy one, and with the potential for flooded streets please check road conditions before heading out. We’ll have an update before sunrise.
NOAA rainfall total estimates for now through Friday evening. (Pivotal Weather)In terms of storm totals, as mentioned, the forecast models are all over the place, but areas around Galveston Bay, including southeast Harris County, probably are at the most risk for heavy rainfall that will quickly flood streets. We’re still looking at likely rainfall totals of 2 to 4 inches for most areas, with higher localized amounts of 6 inches or greater. The region’s bayous are in pretty good shape and should be able to handle most of that. It still appears as though the heaviest rains will clear out of the area by or before noon on Thursday.
I want to preface this post by saying that this is a low-confidence forecast, overall. What we can say with some confidence is that heavy rains are moving toward Houston, and in some cases already moving inland between Freeport and Galveston. This will set the stage for a wet period in Houston from Tuesday evening through Thursday morning. A flash flood watch is in effect, and we are predicting a Stage 2 flood threat for the area. What we are not so confident about are the details—such as where will the heaviest rainfall occur, and will the big bullseyes of rainfall be 6 inches, 10 inches, or more? Let’s take it day by day.
Radar at 3:20pm CT on Tuesday (kktv.com)
Tuesday evening through Wednesday afternoon
We anticipate that this initial round of showers moving into the coast this evening probably will reach about to Interstate 10 before winding down, probably by or before midnight. After this, models are indicating that a more organized band of storm activity will move into the coast between midnight and sunrise Wednesday. This could occur anywhere between Matagorda Bay and Galveston Island, although at this point I’d probably lean toward the southwest, and Matagorda/Brazoria county area. These storms may very well be efficient rain producers, with rainfall rates of 2-, 3- or more inches per hour, which will quickly back up streets.
