Invest 91L Gulf Coast Impact – A hype-free look at the forecast and potentials

Invest 91L is finally getting its act together in the Bay of Campeche. The wave traversed most of the Atlantic with a lot of attention and very little action. Now that it has met up with the tail-end of a front and some lingering vorticity, it looks like it may be trying to get its act together.

The NHC currently gives the Invest a 90% chance of development during the next 7 days. They’re update reads:

Showers and thunderstorms have increased this morning in association with a broad area of low pressure located over the southwestern Gulf of Mexico. This system is forecast to drift slowly northwestward during the next couple of days, and environmental conditions are expected to become conducive for additional development. A tropical depression is likely to form during the next couple of days as the system moves generally northwestward and then northward near or along the Gulf coast of Mexico and Texas through the middle of the week. Interests along the western and northwestern Gulf Coast should closely monitor the progress of this system. Watches could be required for portions of the western Gulf coast later today or tonight. An Air-Force Reserve Hurricane Hunter aircraft is also scheduled to investigate the system later today.
* Formation chance through 48 hours…high…80 percent.
* Formation chance through 7 days…high…90 percent.

nhc.noaa.gov

Looking at satellite data, there is a fair amount of convection associated witht eh area this morning. The Infrared imagery shows plenty of tall, cold cloud tops, but on Water Vapor, it could be argued that convection to the north of the current “center” of the system may be quickly developing.

I put center in quotes because there is no real center to this blob of storms just yet. The term “middle” may be more appropriate, I suppose.

Either way, where the deepest convection forms will likely be where the center forms. So storms developing farther north may impact where the eventual center decides to develop.

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MODEL DATA

If you’re new here or just need a quick refresher, a reminder here: Looking at model data on an Invest is always tricky.

Computer weahter models are only as good as the data you put into them. And when systems are just starting to form or develop, often the available data to put into the model is incomplete. So we can end up – at times – with model data that doesn’t do a great job at predicting the outcome.

That said, here is a look at the available data with some context to help….

Invest 91L track guidance is holding pretty steady across the model tropical model guidance. We have seen a pretty steady set of forecasts suggesting this thing will scrape up the Texas coast and make landfall somewhere near the Louisiana / Texas border.

Intensity modeling has been reasonably steady, too, showing a strong Tropical storms at landfall.

That said, I think there are some places where where we will see some potential movement of the tracka nd intensity forecasts.

Looking back at the Water Vapor imagery, 91L is on the tail-end of a cold front that is going to be exiting the region in the coming days. The current “flow” it is feeling is gentle tug to the northeast, along that boundary.

But with general high pressure aloft in place, it has a good stable environment with not a ton of shear to grow.

But the combination of the convection to the north and the gentle tug it is feeling now, may manifest in some changes down the line and I think it opens the door for a farther east exit path as it moves northward.

On the map above, I’ve annotated the Highs that are going to be in place with Invest 91L riding between the two. Given the fact it’ll be between two ridges and the ridge to the southeast may tug a bit more along with some of the tug from the exiting trough, I think there is a chance that this system drifts farther east than currently shown in the Tropical Models above.

And looking at the Global Models as well as the AI Models, the 500mb maps could generally agree that there is a chance things shift eastward a bit.

This is further echoed by the ensemble model guidance.

But I will add the asterisk & caveat that until we get a center to form on this thing it can be difficult to pin down specifics like where landfall will be. We can talk about percentages and risks just fine. But specifics are still a bit too tough to nail down.

And specifics are going to be the thing that dictates who sees the worst.

How “worse” is the worst? That is also an unknown at this point. Tropical Models shown above have been suggesting a strong Tropical Storm. And the SHIPS Model guidance is suggesting similar.

This is showing a 4x to 8x normal chance that we see some sort of Rapid Intensification during the next 24 to 72 hours.

And, given recent history, I think we can probably trust those numbers. And I would say, we can expect RI to happen in some form or another.

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WHAT DOES THIS MEAN FOR ME, NICK?

Specifically, that will depend on a few things. How strong it gets, how quickly it gets that strong, and where the puzzle pieces are located that will guide the system to the north.

But generally, I think we can say a few things based on your location.

The timeline

Right now, the timeline of events shows this thing getting its act together through the early part of this week and making landfall sometime between Wednesday midday and pre-dawn hours Friday morning.

That is a pretty big window, I know. But it will depend on the track. Given it will be moving northeast, if it takes more of an easterly track, it will take longer to make landfall. And if it slides up the Texas coast, it could make landfall much earlier.

The track

The longer the system stays over water before landfall, the more likely it will strengthen. There is a possibility that the system could intensify as it approaches land, similar to what we saw with Hurricane Beryl, leading to even more significant impacts in affected areas.

If the track moves westward:

• South Texas Coast: Brief heavy rain and gusty winds, but overall impacts will be limited and not severe.
• Southeast Texas: Expect heavy rain, strong winds, some flooding, and potential storm surge, especially in coastal areas.
• Southwestern Louisiana: Anticipate significant impacts, including heavy rain, damaging winds, flooding, and impactful storm surge.
• Southeastern Louisiana: Similar to southwestern Louisiana, with heavy rain, damaging winds, flooding, and impactful storm surge expected.
• South Mississippi: On-and-off periods of heavy rain, gusty winds, localized flooding, and potential storm surge.
• Lower Alabama: Brief heavy rain, breezy conditions, and some coastal surge.

If the track shifts farther east:

• South Texas Coast: Minimal impact, with only some rain and possibly isolated showers.
• Southeast Texas: Rain showers with the possibility of isolated flash flooding and breezy conditions.
• Southwestern Louisiana: Expect brief heavy rain, isolated flash flooding, and breezy conditions.
• Southeastern Louisiana: Significant impacts remain likely, including heavy rain, flooding, damaging winds, and impactful storm surge.
• South Mississippi: Heavy rain, flooding, damaging winds, and some storm surge are possible.
• Lower Alabama: Brief heavy rain, windy conditions, and some storm surge

But beyond those general ideas about the potential outcomes, I don’t think we can say much more at this time about what may or may not happen.

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THE BOTTOM LINE

While this – so far – does not look like a “major, catastrophic hurricane” type of event, that can change quickly. So, for now, please make the effort to check your Hurricane Preparedness kit if you live anywhere from Corpus Christi, TX to Destin, FL and anywhere with 50 miles of the coast between those two areas.

Talk with your family and friends about your storm plan and make sure folks you know are paying attention to the forecast and are ready should the storm pass close to your location.

But that said, these are things you should be doing during Hurricane Season anyway, so for the moment I don’t think any extra precautions need to be taken anywhere along the Gulf Coast because we simply don’t ahve enough information about specifically where this thing will be going.