Eric Berger

Good morning. It’s going to be a beautiful Saturday in Houston, in early September. We totally understand that people are focused on 9/11 remembrances, family gatherings, or other activities today. But there is a potentially serious weather situation developing in the Gulf of Mexico that you need to keep one eye on this weekend. I say potentially because there are some scenarios in which Houston sees only moderate rainfall, and there are others in which we get drenched.

Here’s what we know for sure: It is highly likely that a tropical depression or storm will form over the southwestern Gulf of Mexico within a day or two. This extremely moist system will bring heavy rains, winds, and high seas to the Texas coast beginning late on Sunday. But it’s the details that matter, and we can’t pin those down yet. Based upon the latest modeling and the atmospheric setup, I want to present three plausible scenarios for the next week. As we will discuss, the effects range from mild to extreme, and that’s one reason why it is so difficult to provide an accurate forecast at this time.

Three scenarios

The map below shows the European model’s ensemble forecast for the evolution of the tropical system, which has been designated Invest 94L. It shows tracks from Friday night through Tuesday evening, and I’ve boxed what I consider three of the most likely possibilities. Let’s discuss each of them.

Scenario A: Coast hugger

In this case the storm moves close to the Texas coast on Monday, but perhaps doesn’t come fully ashore. It then moves fairly rapidly to the north and then northeast, bringing its center close to the Houston metro area on Tuesday or Wednesday. In this case we would see higher tides—although probably not too great of a storm surge—and wind gusts of tropical storm force in the metro area. However, the heaviest rainfall would likely fall off the Texas coast and potentially in southwestern Louisiana. In this scenario Houston might see 2 to 4 inches of rainfall, with the 20-inch bullseye remaining offshore.

Scenario B: Tour of Texas

In terms of rainfall, this scenario is more ominous. A likely weak tropical storm would move into South Texas on Monday or so, and slow down for a couple of days. The center would remain close enough to the coast that the storm would be able to tap into Gulf of Mexico moisture. In this case, Houston might expect 5 to 15 inches of rain, with a 20-inch bullseye of rainfall coming somewhere in the area from Corpus Christi to Beaumont. But it’s impossible to say where. The potential for heavy rainfall would linger through Wednesday. Winds and seas would be much less of a factor.

Scenario C: Riding the Rio

It still is possible that the low moves into northern Mexico and basically tracks along the Rio Grande River, dying out after a few days of being inland. In this case the Texas coast would see some moderate rainfall for a few days, but totals for most areas would probably be 2-4 inches, or even less. This scenario seems a little less likely at this time, but it would certainly have the most benign effects for Houston.

Conclusions

So what actually happens? I wish I could tell you. But we’re talking about a tropical wave that has yet to form a semblance of a circulation, so the forecast models are going to struggle with its track. After that, it’s not entirely clear how much the wind shear currently hampering its organization will weaken over the next couple of days as the system moves northwest or north toward Texas. And these are just the beginning of our questions.

The bottom line is that Saturday should see fine weather in Houston. Sunday should start out sunny as well before rain and thunderstorm chances increase during the afternoon and evening hours. After that heavy rainfall is possible through Wednesday, and we just really can’t say how much. But this is a forecast you should be monitoring closely. We’ll have an update later this afternoon or evening.

To set expectations for next week’s heavy rains, we plan on implementing a Stage 2 flood alert on our flood scale, and anticipate this warning will be in effect from Sunday evening through Wednesday. This is what we mean by Stage 2 on our five-point flood scale:

Events falling into this category may cause significant, widespread street flooding across large swaths of the area, flooding numerous cars. Other examples of what we would consider stage 2 events are ones that flood dozens of homes in small, targeted areas or specific neighborhoods. These events are either moderate impact over a large area or high impact over a relatively small area.

A couple of notes on this before we jump into the forecast. First of all, it is quite early to be calling for this, as heavy rain is unlikely to arrive before Sunday night at the earliest. However, since most people probably will check out over the weekend—much of which will be sunny and pleasant—we wanted to give our readers a heads up now. Second, since we are issuing this flood alert early, it is very much subject to change. And finally, the area of greatest risk lies south and east of Houston, so that’s where we think Stage-2 like effects are most likely.

As to the overall forecast, not a whole lot has changed. There remain a number of meteorological variables that we can’t yet predict with great precision, and so the forecast models are struggling with rainfall totals. For example, a model might forecast 15 inches of rain for a location in one run, and drop to 5 inches the next run.

There is fairly good consistency, however, on the overall setup favoring heavy rainfall somewhere in Texas or Louisiana. (Or both!) So if you live within 50 miles of the coast, between Corpus Christi and Lake Charles, you’re potentially under the gun. In terms of accumulations, we anticipate 2 to 6 inches for most locations, but what we’re concerned about is potential bullseyes of 10+ inches. It looks like the most likely period for heavy rainfall will run from Monday through Wednesday.

The bottom line is this: Enjoy your weekend, but also be prepared for the possibility of heavy and potentially disruptive rainfall early next week.

We’ll update on Saturday and Sunday with the latest.

Good morning. Houston should remain in a drier pattern through the first half of the weekend—Friday evening through Saturday morning looks especially pleasant—before much wetter weather arrives by Sunday. As tropical moisture increases, so will rain chances, and we’re tracking the potential for heavy rainfall from Sunday night through the early part of next week.

Thursday

The next weak front is located north of the metro area, but should slide into the region today. There will be a subtle shift in winds from the northwest to the northeast, but skies should remain sunny regardless. Accordingly highs will be toasty today, likely reaching the mid-90s, with the possibility of a few locations seeing the upper 90s. Lows tonight will drop into the low 70s in Houston, with the potential for upper 60s further inland.

Friday and Saturday

This looks like a pretty stunning period, at least as September goes, through about Saturday evening. The driest air should push into the region on Friday, with the potential for dewpoints to drop into the 50s. Expect daytime highs around 90 degrees, with sunny skies, and lows Friday night in the upper 60s across much of Houston.

Saturday night through Monday

The period turns sharply wetter with the arrival of tropical moisture beginning Saturday night or Sunday morning. The overall threat is still not particularly well defined, but a tropical wave should move into the southern Gulf of Mexico this weekend, and associated moisture will push into the Texas coast. The forecast models are hinting at some significant rainfall totals from this, especially for locations closer to the Gulf of Mexico. For now, as a guess, we’re probably looking at rain totals of 3 to 5 inches south of Interstate 10, with lesser amounts inland through early next week. Our main concern is the potential for higher localized rain totals. It’s impossible to say where that will happen, but the potential is there.

After Monday

A fairly wet period should persist into the middle of the week, with sunnier weather potentially returning by Thursday or so. Until that time highs will only be around 90 degrees, with muggy nights in the upper 70s. Those deliciously low dewpoints will be long gone.

Tropics

It’s September 9, so as usual there is a lot of activity in the tropics. But for the western Gulf of Mexico we need only concern ourselves with the aforementioned tropical wave. This feature, which we’ve mentioned several times this week, is now given a 30 percent chance to develop into a tropical depression or storm by the National Hurricane Center. The most likely outcome is that the system will move into the Mexico coast, or possibly south Texas, but we can’t entirely be sure of that yet. In terms of the overall rainfall threat early next week, it probably won’t matter too much.

Good morning. Most of Houston is experiencing temperatures in the upper 60s to lower 70s this morning, with modestly lower dewpoints. This is not exactly fall-like weather, but it’s a reminder that we’re much closer to fall than you might realize. Moreover, there’s another weak front on tap in a day or so to keep our “September-pleasant” weather in place for the rest of the week.

Wednesday

Today will be hot, as drier air allows the air to warm quickly into the low- to- mid 90s under sunny skies. Light northerly winds will shift to come from the east later today, and eventually the southeast. This will herald the return of somewhat muggier conditions later tonight as the first weak front washes out. As a result low temperatures Wednesday night may be a few degrees warmer than Tuesday night.

Thursday and Friday

Another weak front will be on the move Thursday, however, and it should reach the coast by around noon or shortly thereafter. This one should have even a little bit more drier air with it. So while highs on Thursday will warm into the mid-90s beneath sunny skies, lows Thursday night should drop to around 70 in the city, with cooler temperatures in outlying areas. It will be nice. Expect similar conditions for Friday, which should see the driest air of the week.

Saturday

The drier air should hold into Saturday before our air mass becomes modified by the onshore flow. Still, I’m expecting mostly sunny skies for the first half of the weekend, with highs in the low- to mid-90s. Saturday night should be warmer and muggier.

Sunday and beyond

The party ends on Sunday as notably higher dewpoints in the mid- to upper-70s return to the region. Along with this we’ll see an abrupt shift in cloud cover and increasing rain chances. We still don’t have a great handle on rainfall amounts, but daily chances should be about 50 percent beginning on Sunday, continuing through much of next week. Highs will be around 90 degrees each day, with lows in the mid-70s.

Tropics

In the tropics we’re still tracking Hurricane Larry, which will avoid Bermuda and should gradually weaken as it lifts to the north. Closer to home, in the Gulf of Mexico, Invest 91L is moving toward the Florida Panhandle, where it has a 50 percent chance of becoming a tropical depression or storm before landfall. Regardless, it will make for a wet few days in Florida. Finally, we’re continuing to see the potential for a weak tropical system to develop in the Bay of Campeche late this weekend. However there is no real signal in the forecast models that this system will either develop further or move that much northward. Still, its moisture could play a role in our rainfall next week.