Matt Lanza

A tropical storm or hurricane is likely in the western Gulf of Mexico this week (UPDATED)

Next update will be after the 10 AM CT advisory on PTC 6 Monday. Changes overnight were minimal with a track toward the Louisiana coast, minimal impacts to Houston, and more significant impacts in central Louisiana. PTC 6 is expected to become a hurricane before landfall.

Headlines

  • Invest 91L is expected to develop into a tropical storm or hurricane in the western Gulf of Mexico by midweek.
  • The track forecast is generally pointed toward the extreme upper coast of Texas or Louisiana.
  • Coastal impacts are likely between Matagorda Bay and New Orleans.
  • Inland impacts will depend on exact track and intensity, but at this point we do not believe Houston is the primary target of this storm.
  • Heavy rain and flooding on the coast is a good possibility.
  • Invest 92L in the deep Atlantic is not a land concern at this time.

Invest 91L to likely become a tropical storm or more in the western Gulf

UPDATE (4:20 PM Sunday): The NHC is issuing advisories on Potential Tropical Cyclone 6. Their first map is shown below, which we telegraphed a bit in the post below from earlier.

(NOAA NHC)

We continue to watch Invest 91L, which is likely to be upgraded to a potential tropical cyclone this evening by the National Hurricane Center. This will probably mean the issuance of tropical storm watches on the Texas and Mexico coasts.

Key messages from the NHC on Invest 91L this afternoon. (NOAA NHC)

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.

Invest 91L is producing plenty of thunderstorms, but it currently lacks any real organization. (Weathernerds.org)

Look for things to start trying to get in gear later tomorrow.

Track

So where will Invest 91L go once it develops? Some of this will depend on exactly *where* Invest 91L formally organizes. The final track will ultimately be dependent on the intensity which will be somewhat dependent on where it forms, so everything is connected. In general, however, Invest 91L is going to follow the periphery of high pressure centered near Florida.

Invest 91L should basically follow a track briefly NW, then due N, then NE in the western Gulf, which will likely track it toward somewhere in Louisiana. (Tropical Tidbits)

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.

The track density of the various forecast ensembles shows a turn to the northeast occurring off the coast of Corpus Christi, sending 91L probably toward Louisiana or the extreme upper Texas coast. Impacts will be felt at the coast in Texas, regardless. (Tomer Burg)

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.

Rain totals as shown on the European model will likely be highest to the east of the Texas/Louisiana border, possibly extending into Mississippi and Alabama. (Pivotal Weather)

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. More either tonight or tomorrow morning.

Invest 92L

Meanwhile, way out in the middle of the Atlantic, we have Invest 92L, which has 70 percent odds of developing in the next several days.

Invest 92L is going to track generally north, then west-northwest, likely staying out over the open Atlantic. (Tropical Tidbits)

This one will take a day or two to start organizing, but once it does it should track west-northwest, likely strengthening slowly before turning more northwest later this week, probably staying out at sea. For now, interests in the Caribbean islands should keep tabs on this, but it is not currently expected to deliver significant impacts there.

Beyond 92L, we have another wave likely to emerge off Africa later in the week that could develop out at sea in the eastern Atlantic. But there are no other land concerns besides Invest 91L at this time.

Odds of development in the southern Gulf and heavy coastal rainfall increasing next week

Headlines

  • Development of some sort of tropical system is becoming increasingly likely in the western Gulf next week.
  • There are two general thoughts on outcome: Either a better organized system that tracks offshore toward Louisiana or a lesser organized system that tracks offshore but closer to the Texas coast.
  • Either outcome will produce rough seas, gusty winds, and heavy coastal rainfall with flooding possible on the coast.
  • Houston & Corpus Christi proper likely don’t have to worry about significant impacts, but coastal areas between Matagorda Bay and central Louisiana should be on guard for tidal flooding and potential strong winds (mainly in Louisiana).
  • No other notable tropical concerns exist at this time.

Gulf of Mexico development odds increasing

First, a point of clarity: Invest 90L was declassified yesterday, and Invest 91L will be the designation for the tropical disturbance in the Gulf this weekend.

Starting off this afternoon, we have Invest 91L with thunderstorm activity in the southern Gulf but no real organization. We think this will take a couple days to do anything.

Invest 91L is somewhere in the southwest Gulf without a whole lot of organization. (Weathernerds.org)

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. And development odds 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.

Dry air is likely to work somewhat against development and organization. It will almost certainly limit how far inland the heaviest rain can make it next week. (Tropical Tidbits)

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.

Four operational model forecasts on Wednesday morning, with the AIFS & ICON showing a stronger tropical storm or even hurricane risk near Louisiana, whereas the Euro and GFS are weaker and slower (farther south) with more rain in Texas. (StormVista)

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.

Regardless of development, heavy rainfall is likely on the coast of Texas and into much of Louisiana. The inland extent of rain in Texas will be limited, and the gradient, or difference between high and low amounts of rain could be much sharper than shown in today’s NOAA rainfall forecast. (Pivotal Weather)

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.

Elsewhere, nothing else of note in the tropics today.

The Gulf of Mexico remains the hotspot with another soaker on tap next week, with or without a named storm

Headlines

  • Invest 90L will drift south into the weekend and eventually partner up with a tropical wave moving into the Bay of Campeche.
  • Development odds are up to 40% on that as it tries to get started off the coast of Mexico.
  • There is uncertainty on whether it will develop or how close to the coast it will be if it develops.
  • We do not currently see much risk that this becomes a hurricane.
  • Regardless, interests between Mexico and Louisiana should monitor this disturbance, and we are watching the potential for another round of locally heavy rain, with or without a named tropical system.

The Gulf will not stop making noise

The main focus of activity, at least in terms of any practical, meaningful impact of late has been the Gulf of Mexico. After I posted yesterday, the low pressure system was defined as Invest 90L, our second cycle through the list of invests. I would have predicted we’d be on the third cycle through by now. (Invests are numbered 90 to 99 and then repeat, as they’re really just placeholders to run models on)

Anyway, looking at the Gulf today, you can see Invest 90L in all its glory. It’s drifting southward, while a lot of its moisture gets sheared off to the east. Basically, it’s beginning the transition into its next phase of life now.

Invest 90L is a little tough to pinpoint, but it’s technically drifting south, while a lot of the moisture and rain associated with it lifts off to the east and northeast. (Weathernerds.org)

From here, 90L should drift all the way south into the Bay of Campeche where it’s going to finally meet up with the tropical wave we’ve been discussing ad nauseum that’s exiting the Caribbean today. Whether this gets classified as Invest 91L or stays 90L, I don’t know. It’s a procedural mystery. Whatever the case, I’m going to refer to it as 90L.

Anyway, by the time we get to Sunday, this whole mass congeals in the Bay of Campeche. It probably won’t develop right away, but it will begin to stir a bit.

By Sunday, the GFS model above shows Invest 90L or whatever it is organizing in the Bay of Campeche, not far off the coast of Mexico. (Tropical Tidbits)

In general, from here we expect this thing to track northward. I think we stop at this point in terms of talking about specifics. Everything becomes kind of theoretical. If 90L forms farther offshore, it may have a better chance to organize a bit more and track more due north or north-northeast toward extreme east Texas. The stronger it gets, the farther northeast it will go, deeper into Louisiana. If 90L continues to hug the coast of Mexico, as shown on the GFS here, it would likely try to become a tropical storm and then slide inland. A weak system would probably come ashore *in* Mexico, whereas a slightly more organized depression or tropical storm would track more toward the Texas coast.

The ceiling on this is *probably* below hurricane intensity right now, if it develops. Never say never obviously, but virtually all the signals we are getting from tropical models, operational models, and ensemble guidance keeps this as a tropical storm or weaker. So from a “will we see widespread power outages and/or major hurricane damage” perspective, the answer is almost certainly not at this point.

But, I would advise folks between northern Mexico and Vermilion Bay in Louisiana to keep monitoring this through the weekend.

Gulf Coast rainfall concerns

Now, the bigger concern I have with this system is rain. Rainfall over the last 10 days or so has been prolific in portions of Texas and Louisiana.

The percent of normal precipitation over the last 2 weeks has been over 200 percent of normal across much of coastal Texas and portions of Louisiana, as well as interior Texas. (High Plains Regional Climate Center)

The Houston area has been primarily spared significant rain, but Galveston has seen over 10 inches. Louisiana has seen significant totals also. As has Corpus Christi. So there are a lot of vulnerable areas in between some areas that could handle rain fine next week. I won’t post a rainfall forecast because that outcome will depend on if a storm develops and how it tracks. There will be locally heavy rain even without a formal named storm, so no matter what, we’re looking at the potential for another 4 to 8 inches of rain or more in spots next week as this comes northward Tuesday through Thursday.

Bottom line: Check in on this again this weekend.

Elsewhere

There is one system in the deeper Atlantic that has some potential to form next week, but it almost certainly looks destined to track out to sea right now. Either way, it’s so far off and so undeveloped at this point that it’s barely worth mentioning.

Atlantic Canada will see heavy rain and gusty winds from the remains of Invest 99L in the North Atlantic this weekend. That should be fairly quick moving but reasonably noteworthy.

Beyond all that, I don’t see anything of note outside the Gulf right now. We’ll have more tomorrow!

Lemony: A series of unfortunate Atlantic disturbances

Headlines

  • There are multiple areas to watch in the Atlantic, none of which is really a major concern in terms of development.
  • The main place to watch is the Gulf of Mexico, where heavy rain in Louisiana today from a frontal low is causing localized flooding.
  • The Caribbean wave may make a slight effort to develop next week in the western Gulf, but again, the primary concern will be rainfall in coastal Texas and Louisiana as that moisture lifts north and northeast.
  • A return to more “average” basin conditions may unfold late in the month.
Lemons all over the NHC outlook map today, but none of these areas is of serious concern at this time. (National Hurricane Center)

If you asked me in May to tell you what the NHC outlook map would look like on September 5th, I would have said that it would look something like the map above, though perhaps with more orange and red shaded regions and/or named storms. But, busy. If you asked me how many of those areas on that day would be of actual concern, I would have guessed about four. Instead, we got the map, but of the 5 outlined areas, maybe 0.5 is of actual concern — and not even really because it has a chance to develop.

The three Atlantic disturbances are honestly of no consequence. The one northwest of Bermuda (Invest 99L) is likely to track toward Atlantic Canada as a rain maker and gale heading toward the weekend. We’re looking at 20 to 60 mm of rainfall for Nova Scotia, PEI, and portions of eastern New Brunswick from this in addition to rough marine conditions.

Invest 99L will produce some rough marine conditions and locally heavy rain as it moves into Atlantic Canada this weekend. (Pivotal Weather)

The other two disturbances in the Atlantic are likely to stay out at sea and end up on the lower-end of the intensity scale as it stands right now.

Caribbean wave & Gulf of Mexico permalow: Mainly a rain concern

Flash flooding is ongoing in parts of Louisiana as heavy rain associated with a frontal low in the Gulf of Mexico expands north and east today.

Because this low tried to consolidate a bit this morning, the heaviest rain has occurred well offshore with close to 15 inches estimated in some cases.

Estimated rain totals of 1 to 3 inches on the coast of Louisiana and Texas have occurred in the last 24 hours, with heavier rain offshore and farther east around Lake Pontchartrain, where 2 to 7 Inches or more has fallen. (NOAA MRMS)

However, very heavy rain has occurred and is continuing in parts of eastern Louisiana and even southern Mississippi where upwards of 5 to 7 inches has occurred in spots, heaviest between I-10 and I-12 near Lake Pontchartrain and just east of New Orleans into Hancock County, Mississippi. This low will be sheared apart, with one piece heading eastward and another southward over the next 48 hours. The first Gulf Coast cold front of the season arrives in places like Houston and Lake Charles into Mississippi and Alabama this weekend. That will help clear the deck.

So then what? Well, this tropical wave that we’ve been discussing for days now finally makes it into the Bay of Campeche this weekend. It will sit and fester a bit, sort of merging together with the piece of the current system in the Gulf that will also fester down there. And you get another low pressure system. The Gulf is home to a permalow this month. Modeling goes two ways with this. The generally trustworthy European ensembles limit development risk of this area to maybe 40% for a depression and 30% or less for a tropical storm.

Probability of a tropical depression based on the European ensembles is around 40 percent or so (this tends to get overdone a bit) and odds of a tropical storm are 30 percent or less in the Gulf. (Weather Bell)

The storm track would probably be north and northeast toward Louisiana, and the ceiling on this would be low, probably below strong tropical storm intensity. However, more volatile models like the European AIFS (AI model) and ICON (German model) show this developing into a tropical storm, tracking toward Louisiana as well next Wednesday. In the former case, with no real development, we end up with a situation like we saw this week: Heavy rain at times near the coast midweek next week. But no organization. In the latter case with development, we get a coherent tropical storm and heavy rain offshore that crashes into Louisiana next week.

The bottom line: The primary concern next week will continue to be excessive rainfall. Secondary will be tropical development which does not appear to be a serious concern at this time.

GFS model forecast rainfall for next Wednesday and Thursday showing pockets of isolated heavy rain again on the Texas coast, but little to no tropical development. (Pivotal Weather)

The map above is the GFS model forecast for Wednesday and Thursday next week which shows isolated heavy rain on the Texas coast and near Louisiana, very similar to what we’ve seen this week. Even if no tropical development occurs, a localized flooding concern may emerge again next week on the Gulf Coast of Texas or Louisiana.

Beyond all this, there’s not much else doing out there that’s of concern. There are hints that the widespread sinking air in the background of the Atlantic basin may relax a bit in the final third of the month, but we also saw that possibly happening a few weeks ago and it didn’t. So while I would suspect things could turn more active toward October, I also want to be cognizant of the fact that this a forecast we’ve made before that hasn’t panned out. So for now, we’ll call for a gradual return to more normal activity in the Atlantic heading toward October, which is to say not as active as feared this season but more active than it is presently.