In brief: It continues to look as though formation of a tropical storm in the Gulf of Mexico near Texas will happen soon. At this time, the majority of our modeling guidance still points toward the storm’s center remaining off the Texas coast and eventually moving into Louisiana. This forecast could change, however, and we’re watching closely.

Good evening. It has been a lovely early September day in Houston, and we’ve got about 12 hours more to enjoy the dry air before it exits on Monday morning. As first fall fronts go, this one was fairly standard: short-lived, modestly impactful, but nevertheless deeply appreciated. Alas we now probably will have to wait awhile for the next cool front. And so we turn our attention to the tropics where we have a “potential tropical cyclone.” The National Hurricane Center uses this term to designate a system that is close to land, which it expects to develop, and for which it wants to begin issuing public advisories.

It has been nearly a month since the last named storm formed in the tropics, Ernesto, back on August 12. But soon, likely within the next day or so, we will have Tropical Storm Francine in the western Gulf of Mexico. Our confidence is high that a tropical depression or storm will begin lifting north on Monday, and move to within about 100 miles, give or take, of the mouth of the Rio Grande River on Tuesday afternoon or evening.

Not whole lot has changed in our thinking about the forecast today. It still appears most probable that the tropical system will turn north, and then northeastward, remaining off the Texas coast all the while. Yes, this is not a fully locked in forecast, and some uncertainty remains as indicated in the National Hurricane Center’s “cone of uncertainty.” Moreover, due to the storm’s angle of attack, even a subtle shift could bring the storm closer to the Texas coast, or possibly even inland.

However, at this time the most likely scenario is that the center of the system remains offshore and ultimately makes landfall somewhere in southwest or south central Louisiana on Wednesday or Wednesday night. A track toward Louisiana would mean that the system remains over water longer, and this among other factors favors additional intensification. It is possible that a Category 1 or even Category 2 hurricane ultimately makes landfall if the storm tracks toward Vermillion Bay and Lafayette, or further east.

For Houston, our potential impacts range from moderate to not at all impactful. This will depend on how close the center of the storm comes to Houston. Most likely, the majority of the Houston area will see only see modest rainfall totals, perhaps 1 to 3 inches, or even less. The coast could be more vulnerable to heavy rainfall, especially with a closer pass of the storm’s center. But I am not certain that even places such as Galveston Island will see heavy rains from the system. This forecast should be clearer tomorrow.

As for local winds and seas these are highly dependent on the track of this system/Francine. We should have more actionable information here by tomorrow morning. The high end for Galveston Island is probably tropical storm force winds, but I want to see more data overnight and on Monday morning.

Note: We’ll have a comprehensive update on the tropics, as well as a general forecast for Houston next week, first thing in the morning.

In brief: It’s a fantastic day in Houston, with amazing weather—this evening will feel great—and an impressive season opening win by the Texans. Unfortunately, we need to keep one eye upon the Gulf of Mexico, where there is tropical activity. Here’s the latest, via The Eyewall, on what to expect in Texas and Louisiana from the impending storm.

We are continuing to watch Invest 91L, a tropical disturbance in the southern Gulf of Mexico that is likely to be upgraded to a potential tropical cyclone later today or tonight by the National Hurricane Center. This will probably mean the issuance of tropical storm watches on the Texas and Mexico coasts.

The disturbance continues to produce ample thunderstorms in the Bay of Campeche, but it remains a day or so away from actually organizing into a formal tropical entity. Look for things to start trying to get in gear later tomorrow.

From a forecast perspective, this setup is certainly not without nuance, but it does make the track forecast a little more simple. Initially, 91L will track northwest in the Bay of Campeche. From there, as it organizes, it will begin to turn toward the north. Eventually, it should turn northeast, which, depending on where it forms, puts it on a track likely between Galveston and central Louisiana. Again, there is nuance here in that a weaker outcome would lean left, closer to the Galveston-High Island corridor, whereas a stronger outcome would track a bit closer to Vermilion Bay in Louisiana. But for the most part, I think the track forecast is relatively well understood at a high level today.

Trends in the last 24 hours have been toward a slightly stronger storm closer to central Louisiana. But there remains a relatively wide berth of possible outcomes. So don’t write it off in Galveston yet, but it is likely that if it hit Galveston directly, it would be a weaker storm.

Intensity

So let’s talk about intensity. Operational modeling has come around to the idea of a more well developed, stronger storm now. Earlier this morning, most tropical modeling was spread between high end tropical storm and low end tropical storm intensity. This afternoon’s runs have tended to bump this up a little, ranging from weak tropical storm to hurricane intensity. SHIPS guidance, which forecasts the odds of rapid intensification suggests about a 6 to 8 times greater than normal potential of this rapidly intensifying in the next 72 hours. Wind shear looks low, and while sea-surface temperatures are not ballistically warm in the western Gulf, they are at or above normal away from the immediate coastline and more than supportive of intensification. It appears the environment will be favorable for intensification.

Based on all this, we are likely heading for at least a moderate to strong tropical storm and a reasonable chance at a hurricane assuming this tracks as shown above toward Louisiana.

Impacts

Obviously, we’re going to be concerned with tropical storm or hurricane impacts near and especially east of where this comes ashore, which I won’t try to pinpoint exactly right now, but they’re primarily on the Louisiana coast at this time. We will cover that in more detail tomorrow as more becomes known with respect to track and intensity. We should expect waves of 10 to 20 feet offshore with this as it comes north. Gusty winds will occur on the coast between Matagorda Bay and Sabine Pass in Texas, possibly up to tropical storm intensity (35 to 45 mph). Inland locations like Houston should see much less of that. And again, Louisiana will likely see stronger winds. If the storm comes in at Galveston or High Island, there will be stronger winds in the Beaumont-Port Arthur area.

One of the bigger impacts with this storm will likely be rainfall. Somewhere will likely see 10 to 15 inches of rain from this storm with widespread amounts a little under this elsewhere. For Texas, with a track more to the east, this has generally lowered rain totals there. However, that has led to higher totals in parts of Louisiana. The map below shows the European operational model’s forecast of rainfall. Normally, I don’t care to show operational model guidance rain maps, but I think this is a decent representation of risk. The highest totals will be along track and to the east, but the entire coast, even west of the landfall point should see at least some heavy rainfall.

I expect flash flooding to be a concern in Louisiana, which has seen a good bit of rain lately, as well as in southern Mississippi and Alabama. Coastal Texas will be dependent on exact track, but flooding risk doesn’t look overly concerning right now. Still, check in on this again to see if anything’s changed.

Storm surge will also be an issue, but we will await guidance from the National Hurricane Center on that before speculating. And as always, tropical systems can and do produce isolated tornadoes.

At this point, interests on the Texas and Louisiana coasts should continue paying close attention to the forecast updates on Invest 91L or the potential tropical cyclone. The biggest concerns right now are for Louisiana, but continued monitoring is advised in Texas too.

Note: Space City Weather will have a brief update this evening by or before 10 pm CT with the latest.

In brief: A tropical storm is likely to form just off the Texas coast within a couple of days, and it could bring some rains and winds to Houston on Tuesday and Wednesday. How impactful the storm is will depend on how close to the Texas coast it gets. For now, we are leaning toward far enough offshore to avoid significant disruptions in Houston. But the forecast is not locked in.

All of our available data continues to point toward the formation of a tropical storm in the western Gulf of Mexico within the next 48 hours or so. Our confidence is pretty high that by around the Tuesday afternoon to Tuesday night period this system will be positioned 50 to 150 miles offshore the Texas coast, about due east of the mouth of the Rio Grand River.

The question for Houston is, what happens after that?

Over the last several runs, we’ve seen better model agreement in those outcomes. So while I’m not ready to say this is a high-confidence forecast, I do feel as though it is fairly likely to occur. By Wednesday the storm will probably be moving more or less parallel to the Texas coast, to the north-northeast. Then by Wednesday evening or Thursday, the system—most likely a tropical storm, but it’s impossible to rule out strengthening into a hurricane—would make landfall somewhere in southwestern Louisiana.

This forecast can change, and indeed anyone who has followed tropical weather knows to expect the unexpected. Additionally, this area of low pressure that we’re talking about remains a fairy disorganized mass of showers and thunderstorms in the southern Gulf of Mexico as of Sunday morning. The accuracy of the models should increase as a center of circulation forms today and Monday. However, at this time all of our guidance is pointing to a scenario in which this tropical system gets fairly close to the Texas coast, but then remains offshore as it moves to the northeast.

Ok, with those caveats aside, what happens in Houston under such a scenario? Basically the same areas that saw a lot of rain last week are going to see more rainfall. That is, coastal counties will be most at risk for heavy rainfall, with the possibility of picking up an additional 3 to 6 inches. This forecast remains highly dependent on how close the tropical system passes to Houston, of course. A storm closer to shore would nudge the heavy rainfall into all of the Houston metro area, and a storm a bit further offshore keeps the heavy rain away from even places such as Galveston Island.

As for winds and seas, with the storm offshore, the worst of these effects would be to the east of the center. Therefore, while winds and seas should increase along the upper Texas coast, with the current forecast they would not be anything extraordinary. We’re talking something like wind gusts of maybe 30 to 35 mph right along the coast, with lesser winds inland; and tides 2 to 3 feet higher than normal. Remember, both of these effects are very much tied to the track of the storm, so precise forecasts are impossible at this time.

In terms of timing, the most impactful days for Houston’s weather will probably be Tuesday and especially Wednesday.

The bottom line is that, right now, we don’t anticipate major impacts in the Houston area from this tropical system. That could, of course, change. If it does we’ll let you know as soon as our thinking changes. Expect another post later today, from Matt, on the latest forecast and a broader look at impacts for the Texas and Louisiana coasts.

In brief: Development of some sort of tropical system is becoming increasingly likely in the western Gulf of Mexico next week. Generally, there are two potential outcomes: Either a better organized system that tracks offshore toward Louisiana, or a lesser organized system that tracks offshore but closer to the Texas coast. In this post, also published on The Eyewall, we go deeper on what could happen and its implications for the greater Houston region.

The state of play as of early afternoon on Saturday is that we have a fading system in the northern Gulf of Mexico, which was responsible for much of our rainfall this past week; and we also have Invest 91L with thunderstorm activity in the southern Gulf, but no real organization. Our focus should now turn toward 91L, in the southern Gulf.

At some point heading into later tomorrow, Invest 91L will probably halt its southward progress, slow down and begin to make a turn back northward later on Monday. From here, we’re beginning to see some model consensus increasing around this becoming at least a tropical storm by Tuesday or Wednesday. Development odds from the National Hurricane Center have increased to 70 percent as of this afternoon.

As 91L comes north, it will enter a tricky environment from a forecast point of view. On the one hand, you will likely have low shear and warm Gulf waters to help it along. On the other hand, there is likely to be a lot of dry air over Texas thanks to this weekend’s early fall cold front. That dry air works against tropical development. We’ve seen dry air in Texas take its toll on tropical systems before, so that’s one reason to be cautious about some of the more bullish models.

Whatever the case, slow, gradual development is likely late Monday and Tuesday as this comes north about 100 to 200 miles off the coast of Mexico. Modeling is actually in very good agreement on all this through Tuesday morning. From that point, the models diverge. The European model, which I might argue would have a better handle on more of the nuance at play here, tends to develop this slowly. The GFS, ICON, and Euro AI (AIFS) modeling shows a slightly faster development path for 91L on Tuesday into Wednesday.

This poses an interesting forecast challenge. The upper pattern on Tuesday night/Wednesday morning will support steering currents around the periphery of high pressure off the west coast of Florida. This should allow for a north and northeast track in the Gulf. A stronger storm would probably be more apt to take that northeastward movement, where as a weaker storm may come more due north. We see this as both the ICON and AIFS show a faster, stronger storm farther out in the Gulf headed toward Louisiana, whereas the European model keeps it weaker and close to the mouth of the Rio Grande River.

The GFS eventually caves and strengthens it, allowing the system to follow the AIFS/ICON group toward Louisiana, whereas the European model just brings it into Texas as a depression or low-end tropical storm.

Obviously, this gives us a forecast challenge, but I think we’re in two very distinct camps right now.

• Camp 1: A strong tropical storm or hurricane that tracks off the Texas coast toward Louisiana arriving Wednesday-ish.
• Camp 2: A depression or loosely organized tropical storm with a lot of rain that impacts Texas, especially at the coast Tuesday through Thursday, coming ashore between Galveston and Cameron, LA.

I am not a betting man, but I would probably say the odds right now are 70/30 in favor of camp 2, but that 30 percent is a weighty one given that the system could be a hurricane in that scenario. Normally, I’d discount the ICON model, but given its performance this season and the consistency it has had with track and intensity here, I think there’s merit to considering it with this particular system.

So what do you do? You check back in again tomorrow for more. If you’re in Louisiana, it’s probably a good idea to make sure you have your hurricane kits up to date and know what you’ll do in the lesser chance this comes your way as a stronger storm. In Texas, I think Houston and Corpus Christi are fine. However, I think folks from Matagorda Bay through Sabine Pass along the coast and bays should probably be aware of both a rainfall flooding risk and a tidal flooding risk that may develop from this. More to come.

Note

We’ll continue to monitor this storm closely. If the forecast materially changes, and we are likely to see more directly threats in terms of wind and surge in the Houston area, Space City Weather will publish an update early on Sunday morning. If the forecast remains more or less the same, look for an update later in the day.