We continue to monitor Invest 94L Potential Tropical Cyclone 14 Tropical Storm Nicholas in the Bay of Campeche, which is likely to become a tropical storm before the day (or possibly the morning) is out. As I write this, hurricane hunters are investigating the storm and they have found tropical storm force winds, and subsequently they have tagged this as a PTC, as it lacks a defined low level center. In other words, it quacks like a duck but it doesn’t yet look like a duck, so we can’t technically call it a duck. But from your perspective, it’s basically a duck. Sorry, Ohio State fans.

Nothing better than writing a bunch of stuff only to have it get blown up. Anyway, we now have Tropical Storm Nicholas. Here’s the forecast track from the National Hurricane Center.

With the formation of Nicholas, we now have Tropical Storm Watches along the coast and in Galveston Bay. The initial read on Nicholas from the NHC is to strengthen it to a moderate to strong tropical storm before making landfall somewhere between Rockport and Sabine Pass. The Matagorda area is favored at this time, but that could always change.

From our vantage point: First, we will be holding this at a Stage 2 flood event. Given the higher end risks and uncertainties involved in this forecast, it’s important to note that this is pretty low confidence. We would continue to skew this as lower risk for a Stage 2 event north and west of Houston and higher risk south and east. In other words, the farther south and east you are in the metro area, the more likely you are to receive heavy rainfall that could produce flash flooding. Or at least that’s our going assumption sitting here today.

Sunday/Monday

Next, let’s talk briefly about today and tomorrow. We are expecting thunderstorms at times, especially along the coast. And those could easily produce 2 to 3 inch per hour rainfall rates which could cause flash flooding eventually. It’s important to note that this rain today and tomorrow is indirectly related to Nicholas, and what we see on Tuesday into perhaps Wednesday would be directly related. In other words, we are expecting multiple rounds of rain and storms between now and Wednesday. If you don’t get rain today or tomorrow, that doesn’t mean you won’t on Tuesday or Wednesday and vice versa.

The Weather Prediction Center arm of NOAA has placed the southeast metro in a slight risk (level 2 of 4) of excessive rainfall today and the bulk of the metro area in that slight risk tomorrow.

This means that there is at least some chance that we get enough rain to produce flash flooding in spots today or tomorrow. Rain will likely fall at the rate of 1 to 3 inches per hour in the heaviest storms, and any storms that linger awhile or “train” repeatedly over the same areas could begin to produce some street flooding. This would be most likely at the coast or just inland today and tomorrow, but some risk exists farther inland as well tomorrow.

How much rain do we expect today and tomorrow? Well, here’s the official NWS outlook for rainfall through Tuesday morning.

We would expect to see about 3 to 5 inches of rain along the immediate coast with 1 to 3 inches inland. There will likely be isolated higher amounts in here — through late Monday night or Tuesday morning.

Beyond Monday night

Here’s where forecast confidence drops a good bit. When we have tropical storms we often tell you not to focus on the center line because impacts will extend far from the center. That’s as true as always with this storm, but the reality is that: Because of the angle at which this is coming up the Texas coast, that track actually really matters in terms of what we experience in the Houston area and coast on Tuesday into Wednesday. Why is this? We can look at two goal posts here to get a sense of why this is important.

Last night’s GFS model took the storm into Cameron Parish, Louisiana and because it spent a lot of time over water, it basically intensified it into a hurricane. But! Because it tracked offshore, the bulk of the tropical storm and hurricane force winds stayed offshore, and Galveston saw just moderate tropical storm conditions. The Euro brings the system inland over Matagorda and because that’s far enough south Galveston again just saw moderate tropical storm conditions on that run. But from a rainfall perspective, the farther east GFS directs most of it into Louisiana, while the west tracking Euro brings it more into the Houston metro area.

The final track of Nicholas will be dictated by where exactly the low level center forms. So in terms of Houston rainfall, a solution like the GFS provides minimal impacts Tuesday and Wednesday, whereas the Euro implies significant risk of flash flooding. It’s important to note that both solutions imply heavy rainfall risk is likely along the immediate coast, so for places like Galveston, you should expect at least another period or two of heavy rain Tuesday into Wednesday regardless of the exact track.

The good news is that with a defined tropical storm now and hurricane hunters continuously investigating, and better data going into our models, we should have some clarity on this by tonight, or so that’s the hope!

In terms of tropical impacts: Based on the track above. Winds will likely approach 30 to 40 mph at times beginning late Monday night or early Tuesday along the coast. Winds will likely be sustained at 30 to 45 mph on the coast Tuesday, with gusts of 45 to 55 mph possible. Higher winds are possible with a stronger storm or one that splits the model difference right now and comes ashore near Galveston. A storm tracking farther east would likely result in slightly less wind at Galveston and more impacts to Port Arthur or Cameron, LA. Inland winds should remain below tropical storm force, but it would likely be a breezy day at times on Tuesday, especially south and east of Houston. This doesn’t appear to be a major power outage risk event for the majority of the Houston area, but coastal areas could have a few issues.

Tides are going to approach levels of about 3 to 5 feet above mean low lower water (MLLW). This may lead to impacts close to what you may have experienced during Tropical Storm Beta almost exactly one year ago. This is mostly minor coastal flooding. If Nicholas does intensify beyond current expectations or come ashore closer to Galveston, tides could be a bit higher and flooding would become more of a concern along the bay communities as well as in Galveston, Surfside, and Bolivar.

So just to summarize:

• Periods of heavy rain, indirectly associated with Nicholas are likely today and tomorrow, with the highest amounts likely closer to the coast. Flash flooding is possible with those storms.
• An additional period of heavy rain is likely on Tuesday into Wednesday, contingent on the exact track of Nicholas. That is where we have significant forecast uncertainty still. Additional, possibly more significant flash flooding is possible then.
• Tropical storm conditions are becoming more likely along the immediate coast, with Galveston likely to experience tropical storm conditions on Tuesday. At this time, we don’t expect inland locations, including the city of Houston to see significant wind, though it will be a bit breezy Tuesday.
• Minor coastal flooding is likely, with impacts possibly similar to what was seen during 2020’s TS Beta. A stronger storm or a storm closer to Galveston would likely yield slightly worse impacts, but a storm passing east of our area may reduce impacts some.
• We expect better model data this afternoon and evening to hopefully help boost some forecast confidence.

Eric will have the latest based on morning model data around 2 P.M. today, and we’ll have another post this evening as well.

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Ok, now on to the forecast. With this evening’s post we are going to give a general sense of the timing for what to expect, and when. We have some answers about the near-term forecast through Monday, but the bigger and perhaps more important question concerns what comes in the middle of the week.

Invest 94L

As of Saturday afternoon, the Gulf storm, or Invest 94L, remains poorly organized (see for yourself). It is difficult to assign a center to the low pressure system, and this lack of definition is one reason why forecast models are struggling a bit. However, the overall picture seems fairly clear. As the system moves northwest across the Bay of Campeche, it is likely to become better organized on Sunday, and should become a depression by Sunday night or Monday. By that time it should be approaching the northern Mexico or southern Texas coast. After this things the forecast becomes murky. By Monday night or so, the system may either move inland near the Rio Grande River, or turn northerly and track up the Texas coast. If it remains offshore, Invest 94L has a chance to become a reasonably strong tropical storm on Tuesday.

Sunday

Skies should remain mostly clear overnight, but clouds will begin to build across the upper Texas coastal region on Sunday. However, for much of the day any showers and thunderstorms we see should be scattered in nature.

Monday and Monday night

By Sunday night or Monday morning we should start to see more organized storms moving in from the southeast, off the Gulf of Mexico. It’s important to note these rains will not be directly related to the core of Invest 94L, which will remain far to the south. However, as a slug of moist tropical air moves inland we should see widespread accumulations of 1 to 3 inches for inland areas, and 3 to 5 inches of rain for coastal counties. We can’t rule out some bullseyes of 7+ inches. It seems possible that this initial round of storms may wind down on Monday evening or over night.

Tuesday and Wednesday

The real question is what comes after this point, and that will be determined by what the center of Invest 94L does. If the storm’s core moves up the Texas coast (the “Coast hugger” scenario in this morning’s post), our region would probably see manageable rain totals on Tuesday and Wednesday, with the heavier rains offshore or falling over southwestern Louisiana. However if the low moves into Texas and then wanders upward through state—perhaps along the Highway 59 corridor or further inland as in the “Tour of Texas” scenario—we could see a second round of even heavier showers on Tuesday night and Wednesday. For now, it is impossible to say which of these situations will play out, but ultimately this is probably the most important thing to watch in terms of flooding for the greater Houston region. If we’re going to get rocked, it probably would come then.

Our confidence is reasonably high that the rainfall event, whatever comes our way, will begin to wind down on Wednesday afternoon or evening.

Matt will have a full update in the morning, and we’ll have all-hands-on-deck coverage with myself, Matt, and Maria tomorrow.

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.