Heavy rainfall coming to the Houston region this week

The big weather story for our week will be a slow-moving tropical system pushing into Texas beginning late Monday, and bringing the potential for heavy rainfall from Tuesday through Thursday. It still is not entirely clear where the heaviest rain will come, but there definitely is the potential for some 10-inch bullseyes, or greater. The region most likely to see this rainfall is somewhere between Matagorda Bay and Beaumont. We are more concerned about this event than we were on Sunday, and are forecasting it to be a Stage 2 flood event.

Latest NOAA rain accumulation forecast for this week in Texas. (Pivotal Weather)

As of Monday morning, here are rainfall predictions from the National Weather Service and NOAA Weather Prediction Center for this system, and we see no issue with these forecasts after looking at the current models:

  • Widespread rainfall of 3 to 6 inches through Friday
  • Some areas are going to see amounts of 6 to 9 inches, with isolated amounts in excess of 12 inches possible.
  • Rainfall rates of 2 to 3 inches per hour are going to be common during the event, which will quickly back up streets and push water into yards.

One problem with forecasting the locations facing the greatest rainfall threat is that this tropical system probably won’t move too much until later this week, as high pressure to the region’s north should allow it to meander for a couple of days.

To be clear, this is most definitely not a Hurricane Harvey type situation—it will not produce anything like Harvey’s totals, nor over such a large area. There also remains a reasonable chance—perhaps 25 percent—that the forecast busts and most of Houston sees 1 to 2 inches of rain this week. However at this time we definitely see the potential for flooding and are classifying this as a Stage 2 flood event on this site’s flood scale. For now, we don’t envision significant home flooding, but these are definitely “turn around don’t drown” conditions, during which isolated underpasses and high-water crossings may become life threatening.

We are forecasting a Stage 2 flood event for Houston this week.

The general pattern we can probably expect is for scattered showers on Monday and likely most of Tuesday. The period of greatest rainfall threat will probably come from Tuesday night through Thursday—with some of the latest models pinpointing Thursday as the day of biggest concern. Days will be mostly cloudy otherwise, with highs of around 90 degrees. Partly sunny skies should return by the weekend.

For those who live along the coast, we also have some high-water concerns as the low pressure system approaches Texas. According to the National Weather Service, through Tuesday morning, low lying areas along the immediate coast may experience minor coastal flooding during high tide times. Additionally, strong rip currents along Gulf facing beaches, and minor flooding along flood prone roads such as Highway 87 near High Island and Blue Water Highway may be possible.

We will update accordingly throughout the week.

Sunday update on tropical disturbance tracking toward Texas

A broad area of disorganized showers and thunderstorms continues to move westward across the Gulf of Mexico, and should push into the Texas coast late on Monday or early Tuesday, based upon present trends. As it has so far failed to coalesce into a better organized system, the National Hurricane Center has dropped the chance of development to 10 percent. However, this was never really the issue with this system—as mentioned on Saturday our concern with this tropical swirl has been moisture and precipitation rather than winds and storm surge.

National Hurricane Center update on Gulf disturbance.

It is quite hard to say how much rain the Houston area, and by extension, the Texas coast will get. Much of the model guidance is fairly well behaved, bringing 1 to 3 inches to the coastal areas of the state from Monday through Thursday. The best rain chances are most likely around the Coastal Bend of the state, including the Matagorda Bay area. However, there are some outlier forecast models that bring quite a bit more, like 5 to 10 inches (i.e. Canadian and ICON models) and to different parts of the state. It is hard to totally discount these outliers given that this is a a fairly slow-moving system, and will be bringing a lot of tropical moisture with it.

NOAA’s rain accumulation forecast falls into the “80 percent” category discussed below. (Pivotal Weather)

Until the models come into agreement it’s hard to have too much confidence in what will happen. I’d say there’s an 80 percent chance, roughly, that most of the Houston metro area sees 1-3 inches of rain this week—which is fine, the region needs the rain and the cloud cover should knock high temperatures down to around 90 degrees. But there is probably a 20 percent chance that we’ll see somewhat more rain than that, and attendant flash flooding on roadways and such.

For planning purposes, expect he heaviest rainfall to begin on Tuesday, and probably run through Thursday morning. If this outlook changes dramatically, or we get some more clarity in the forecast, we’ll update later today.

Tropical system may bring heavy rain to Texas next week

Some readers may note that the National Hurricane Center has begun tracking an upper-level low pressure system over the eastern Gulf of Mexico (note, this is distinct from Tropical Storm Humberto). This is because the forecast models have gotten a little bit more excited about the possibility of this system evolving from a low pressure system in the upper levels of the atmosphere into a low pressure circulation at the surface.

National Hurricane Center tracking map for 7am CT Saturday.

The hurricane center gives this feature a 30 percent chance of developing into a tropical depression or storm as it moves westward toward the lower or central Texas coast, probably coming ashore on Monday or Tuesday.

I’m sure there will be a lot of hoopla about this system over the next couple of days, and some of that is justifiable because one never likes to see low pressure over the Gulf of Mexico in mid-September. With that being said, this one has a long way to go before becoming organized. All of the best global models keep it at tropical depression status right now. So while we cannot rule anything out. I am reasonably confident that we are not looking at a situation in which a hurricane approaches Texas early next week.

Satellite image of the Gulf system on Saturday morning. (NOAA)

However, even disorganized tropical systems can produce heavy rainfall, and that will be a threat along the Texas coast beginning on Monday. How much of a threat remains to be seen, as there is a considerable spread in the model forecasts. The European model paints a bullseye of 4-6 inches around Matagorda Bay and Victoria, with lesser amounts north and south of there, including for the Houston region. The GFS model keeps totals mostly confined to 2 to 3 inches along most of the Texas coast. Another model we’ve been following more, the Germany-based ICON forecast system, keeps the heaviest rain offshore but does bring 4 to 6 inches into Harris County during the middle of next week.

Cumulative precipitation forecast for next week from the GFS model. (Weather Bell)

The bottom line is that we are not overly concerned about development of this system into something that threatens Texas from a wind or surge perspective. However, we are watching for the potential for heavy rain during the Monday through Wednesday period next week. We’ll be watching it closely and updating accordingly.

Hot and mostly dry weekend, with an update on the tropics

Over the last 5 days, most of us have seen at least some rainfall with a smattering of storms each day. Not all of us have seen significant rainfall, however.

Feast or famine in the rain department over the last 5 days. Some places have seen 2 to 3 inches, while others have seen next to nothing. (Harris County Flood Control)

Apologies for the map that is clearly excluding some parts of the area. If you’d like a bigger view, you can view recent rain totals at Harris County Flood Control. Amounts of up to 2 inches or so have occurred near Acres Homes, Sugar Land, and out by Katy, with higher amounts in a few spots near there. Then, you have spots like the East End, far northwest Harris County, and some pockets south and also northeast of Houston that have registered little to no rain at all. For those seeking rain, we’ve got nothing good to report for the next couple days.

Today & weekend

Today and tomorrow should be fairly straightforward forecasts. We should see ample sunshine and hot temperatures. Look for daytime highs in the mid- to upper-90s both days. Nighttime lows into Saturday morning should get to the mid- to upper-70s. If we’re looking for a bright spot in the relentless heat, it’s that the nighttime temperatures and humidity levels will not be terribly oppressive. Heat index values should be mostly under control.

High temperatures on Saturday will probably hit the upper-90s in most of the area. But humidity will not be terrible. (NWS forecast via Weather Bell)

Sunday gets a tiny bit trickier. Moisture from an area of low pressure in the upper atmosphere will take over most of the western Gulf but primarily offshore. We should see at least a few showers being flung toward Galveston and other areas southeast of Highway 59/I-69 on Sunday morning or afternoon. But most places will probably stay dry. We’ll start in the 70s and end in the mid-90s.

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