Eric Berger

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.

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.

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.

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.

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.

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.