Matt Lanza

Increasing risk of a central or eastern U.S. Gulf Coast impact from a tropical system late this coming week

Headlines

  • Odds of tropical development next week are increasing, likely beginning Tuesday or Wednesday.
  • There is a growing consensus among modeling that this system has the potential to strengthen a good bit as it comes northward and is likely to accelerate toward the central or eastern Gulf Coast late in the week.
  • The odds of a system getting buried in the Bay of Campeche are lessening.
  • The odds of an impact to Texas are lessening.
  • People on the Gulf Coast between Louisiana and Florida should be following forecasts closely and beginning to think about their plans for the upcoming week should they need to evacuate or hunker down.

Odds of development increasing

The National Hurricane Center continues to raise the odds of tropical development over the next seven days. We’re now up to a 60 percent risk of development.

Tropical development odds continue to inch up, with development possibly initiating around Tuesday of this upcoming week. (NOAA NHC)

Again, this is a rather conservative view of things, and I anticipate we’ll see this continue to inch up today and tomorrow and push into the “2 day” development map tomorrow or Monday. Modeling is beginning to coalesce around the idea of development north of Honduras or just east of Belize, or on the Caribbean side of the Yucatan. The general theme of the models since yesterday has been to align more with the faster, stronger solutions which would be apt to bring a storm north or north-northeast across the Gulf of Mexico and toward the coast between Louisiana and Florida. There is still a good deal of uncertainty on specifics here, including whether or not it develops. There is still a minority of ensemble members in modeling that struggle to get this going. Not likely to happen, but it’s a non-zero possibility. I just want to highlight that there are reasons this isn’t a 100 percent chance of development right now.

A potential threat to the U.S. Gulf Coast

All that said, I just want to make clear right now that this has the potential to be a strengthening storm in the Gulf, moving north, fairly fast later this coming week. When Francine moved into Louisiana it passed over warm but not super warm waters in the central and western Gulf of Mexico. If this upcoming system tracks farther east of Francine as seems likely, it will be passing over much warmer Gulf waters.

The Gulf of Mexico as a whole is just shy of record warm levels, and most of that is being driven by the waters in the eastern Gulf. (University of Arizona)

The near-record warmth of the Gulf is being driven almost entirely by the eastern half of the Gulf of Mexico, close to where this system will likely pass.

I don’t want to overstate the risk at this point, but given the scenario (Quick moving, very warm water, generally favorable upper level conditions, and less dry air than Francine contended with), there is some legitimate risk of a significant storm on the central or eastern Gulf Coast late next week. You should be following this forecast closely if you live between Florida and Louisiana, and you should be ready to put your hurricane plans into motion quickly this week once we see further agreement on possibilities.

So what do the models say?

We have seen the operational models reduce the spread between each other considerably in the last 24 hours. We still have some variability on track and timing, but there has been a tendency to push toward a track northward between Louisiana and Florida sometime between Thursday and Sunday next weekend. The odds of the system getting buried off the Yucatan in the Bay of Campeche has dropped off some since yesterday.

Today’s European ensemble at 12z, hot off the presses still shows a very wide spread of possibilities, from a system getting buried in the Bay of Campeche to one tracking southeast into South Florida. But what I pay attention to with these runs is what has changed or where the “clustering” is occurring. If we compare the same image at the same time 24 hours ago, we can see a shift in both the ensemble mean (solid black lines) to the northeast and a decline in the number of Euro ensemble members that bury this system in the Bay of Campeche.

A comparison of yesterday’s Euro ensemble mean and individual member forecasts for next Thursday evening versus the same view today shows a marked shift to the northeast with the mean and fewer members in the Bay of Campeche, an indication that trends are shifting north and east in the Euro, closer to what the GFS suite has been showing. (Tropical Tidbits) (Editor’s note: This image was adjusted at 4:45 PM CT Saturday to align the forecast times which were previously askew by 6 hours)

This further indicates that there is a definite trend toward a faster and more progressive storm to the north or northeast within the modeling. We can see further evidence of this in a consistent GFS, the ICON, and the Euro AI model (AIFS) showing similar type of outcomes now.

Why is this? Since yesterday, we have seen a bit of a signal in modeling for a cutoff low or secondary trough to develop over Arkansas or Oklahoma. This is something of a new wrinkle.

The last 6 runs of the Euro ensemble mean showing a developing and farther east trough or cutoff low over Arkansas that is likely helping to “pull” the tropical system straight north. (Tropical Tidbits)

Whatever the case, this slightly stronger and farther east trough is helping to “pull” at the tropical system in the Gulf and force it to the north. This is what is likely shifting the Euro ensemble to the side of the GFS and other modeling now and why we’re seeing some additional agreement develop on a threat to the central or eastern Gulf Coast.

The bottom line: There is building agreement in the modeling that a tropical system is going to come north late this coming week toward the central or eastern U.S. Gulf Coast. While details remain elusive there is enough evidence of a threat to that region that folks should be paying close attention to forecasts and thinking about their plan for later this week should they need to evacuate or hunker down. We’ll have more on this tomorrow.

Trying to narrow down the development setup next week near the Yucatan

Headlines

  • We are likely to see development in the Caribbean or near the Yucatan next week.
  • Model guidance suggests that there are a few possible outcomes, including a quicker, stronger storm that tracks north or northeast or a slower, weaker outcome closer to the Yucatan.
  • Folks on the Gulf Coast, particularly between New Orleans and Florida should be flexible with their preparedness plans and be ready to implement them if necessary early next week.

We are still a few days from Caribbean development

I feel like we’ve been talking about this potential development in the Caribbean for days now. That’s one element of hurricane season that has gotten worse in recent years: The availability and democratization of weather data has kept any and every potential disturbance in the conversation for a week or two before they even form, then for a week or two as they do their thing. In some cases, you can be talking about one system from pre-inception to finish for a month! But the availability of all this information has made our job more important to help y’all make sense of what it’s saying.

The probability of Caribbean development remained at 40 percent this morning. We’ll see if the afternoon update in a bit increases those odds. (NOAA NHC)

Yesterday’s post has aged pretty well, thankfully. Frankly, not a whole lot has changed. But I think there’s a clear dichotomy taking shape now between the European modeling and the GFS modeling Yesterday, I noted how the Euro was apt to consolidate the disturbance next week near or over the Yucatan, whereas the GFS did so mostly in the Caribbean. Those models have not changed their view on this today. Trends over the last couple days have led to the European AI modeling, the AIFS to trend a little closer to the GFS solution of stronger, faster, more north and east. The ICON model is also taking that stand, so there is some slowly building support for the GFS here, I think.

The last 5 AIFS runs showing an erratic but general trend toward the more eastern outcomes for late next week. (Tropical Tidbits)

That said, if we look at ensemble guidance, there continues to be a gigantic split among the 30 to 50 ensemble members in both the GFS and European suite. The Euro seems to be split about 80/20 favoring the western/weaker outcome, whereas the GFS is more of a 40/60 blend favoring stronger and more east/north leaning outcomes.

Latest 12z GFS Ensemble outlook shows about a 60/40 or 70/30 type split in outcomes favoring a stronger, more east and north type track over a system that stays stuck near the Yucatan. (StormVista)

It may have even gotten more confident in that eastward lean in today’s 12z model guidance as seen above. The one big, big takeaway from both of these examples showing the AIFS and GFS Ensemble members is that there is still *very* little agreement on track, just many generalizations that can be inferred from this output.

I continue to think this sort of scenario favors either a Mexico or Yucatan impact or a Florida through New Orleans type impact on the northern Gulf Coast. I remain convinced that Texas is *not* the most likely outcome here, but I would continue advising Texans to monitor things heading into next week.

There are also gigantic timing differences here. The storms that come north and northeast tend to do so quickly, with impacts possible as early as next Thursday. So for folks in Louisiana through Florida, you would need to be ready to act as soon as Monday if this looks like a building threat. For Texas and Mexico, if the western outcome happens, this would likely remain a middling system for several days before organizing later next week and coming north next weekend. This would deliver impacts to the central Gulf Coast by next Sunday or so. That’s a large spread of timing options, so folks on the Gulf Coast should be flexible with their preparedness and be ready to act early next week once things become clearer.

We will have daily posts this weekend to keep you all informed.

Elsewhere in your tropical Atlantic!

Invest 96L has developed in the open Atlantic, and between it and the remnants of Gordon, we could maybe see something try to form over the next few days. Neither system is likely to impact land.

More interestingly, we have potential for a Cabo Verde system to develop later next week. The European ensemble has been quite bullish on this. There is plentiful support for this from other modeling as well. Expect this potential to show up around midweek next week.

The Euro ensemble, as well as other models show a growing likelihood of development later next week off Africa. (Weathernerds.org)

Now, is this system likely to be a land threat? It’s too early to say definitively, but the current thinking is that this would probably end up moving out to sea ultimately. Plenty of time to watch. No other threats are seen closer to home right now after next week’s Caribbean/Gulf story.

Taking a closer look at how next week’s Caribbean or Gulf development might behave

Headlines

  • Model support for development in the Caribbean or near the Yucatan is increasing next week with development likely to begin after this weekend.
  • Models continue to disagree significantly on track outcomes and intensity outcomes, not to mention timing outcomes with weak solutions, strong solutions, late week solutions and next week solutions all on the table.
  • We explain below why Texas is not currently favored but should still at least keep tabs on things.
  • No other significant tropical concerns exist beyond this feature.

Honing in on Caribbean possibilities

Apologies for the late post today. As many of you are well aware, Eric and I both have day jobs which occasionally do have to take priority! The good news is that not a whole lot changed between late morning or afternoon and this evening, which is to be expected when a storm is about a week or more out.

Yesterday, I noted how modeling did not exactly seem helpful at this point because there had been much bouncing around, little strong ensemble signal, and no one model being more consistent than others. Today, let’s re-evaluate things and also take a look at the upper air pattern that may be in place around the time this system develops in the Caribbean. First, I also noted yesterday that the NHC tends to be conservative with development odds this early in the game, and the 20 percent was probably a little low in reality. Well, they’ve doubled those odds today, and we’re now at 40 percent.

NHC odds of development are up to 40 percent now over the next week with the Caribbean disturbance next week. (NOAA NHC)

The Hurricane Center has to do things fairly by the book, which is understandable. The biggest reason I think their odds are not higher is because we’re talking “over the next seven days.” If it were over the next 10 days, I might say this would be up and over 50 percent. Either way, we’re kind of getting way too in the weeds of nuance: The takeaway is that development odds are elevated and continue to increase.

We still don’t have a disturbance to latch onto. We tend to take this for granted sometimes. Weather models are literally sniffing out a disturbance that has not even formed yet and sending up caution signals that something will form, and they’ve been doing it for days. That’s pretty wild. Anyway, all we have is an area of disorganized thunderstorms in the eastern Pacific and near Panama.

Disorganized thunderstorms will likely persist for at least another 2 to 3 days before any sort of consolidated development attempts to begin. (Weathernerds.org)

Over the next few days, we’ll probably see this mass of thunderstorms wax and wane but generally persist in this area. It will gradually ooze northward into the weekend before any sort of attempt at consolidation occurs. When and where that happens is critically important for the future of this system. If those storms end up a bit west and more focused near the Yucatan, then development will struggle to occur. If that occurs a bit east, more into the very warm waters of the northwest Caribbean, then development and organization may begin to occur more rapidly next week.

The problem with these gyre-type systems is that modeling struggles in telling us where that consolidation will occur. For example, the 12z European model today takes the western track of things and basically buries this over the Yucatan or Bay of Campeche for a few days before eventually blowing it up over the western Gulf. The GFS on the other hand does this closer to the northwest Caribbean, which leads to a stronger storm quicker and a more eastward leaning track into Florida.

12z Euro and 18Z GFS operational model guidance presents a good example of the forecast risks with this system, as one keeps it weaker and to the west, while the other goes farther east faster. (Tropical Tidbits)

For those curious about such things, the ICON model leans toward the European model, while the ECMWF AI model, the AIFS is more apt to split the difference between the two possibilities. We can get a sense of timing with this now too. The faster GFS brings this across Florida next Thursday/Friday, while the Euro keeps this sitting in the western Gulf through at least next weekend. So not only do we have limited track confidence, we also have limited timing confidence.

Sidebar: If you are planning a trip to the Caribbean next week or weekend, I cannot tell you what to expect right now. You will need to monitor the forecast, stay in touch with your hotel or cruise line, and just be prepared for some disruption potentially. Everyone has unique circumstances and we just can’t get to every trip question.

Anyway, let’s take a quick look at the ensemble guidance from earlier today. The European ensemble shows nicely what I explained above. A bunch of the 51 ensemble members follow the operational Euro and keep this buried in the Bay of Campeche, while a minority are more GFS-like and go toward Florida or the eastern or central Gulf.

A bit of an ensemble “bifurcation” exists with a majority weaker/westward cluster and a minority stronger/northeastward cluster. (Weathernerds.org)

So, there remains significant spread in possibilities with this system and no one should ignore it on the Gulf Coast for now. But any land impact should not occur before next Thursday, outside of perhaps the Yucatan or Cuba.

Bottom line: Interests along the Gulf Coast should continue to monitor the progress of this system as it evolves over the next week.

The Texas angle on all this

With so many readers in Texas, I just want to jump in here and explain why I think we should continue to watch this storm — but should not lose sleep over it. The other aspect of this setup that will be critical to where it goes is how strong and deep troughing over the Eastern U.S. gets. A deeper trough means a stronger push of cooler air and a much easier scenario to “capture” the storm. The GFS shows this rather progressive pattern outcome. The Euro does too to some extent, but because the storm is weak and over the Yucatan it gets left behind and has to wait for the next one.

Caribbean system likely to get trapped between two areas of high pressure. The strength of an incoming trough, in addition to the position and strength of the system itself will help determine where it goes. (Tropical Tidbits)

You can see this on the Euro ensemble panel from day 10 above, next weekend. High pressure over west Texas and the Southwest will impart a north to south component to the steering currents, while high pressure to the east of the system will impart a south to north component. This effectively cancels out any real storm motion, and it will probably be at the whim of whatever comes through the Eastern U.S. or it has to wait for that pattern to change.

So if you live in Texas and you look at the Euro and the ICON model and see this thing inching west or northwest, it would be natural to start to panic. However, when you look at the bigger picture, the sense I have right now is that this is going to take a hard right turn before it would get to Texas. Of course, that’s not great news in Louisiana or the eastern Gulf through Florida. So, yes, we should continue to watch this for changes, but the upper pattern supports a slow movement until an upper level trough can grab this thing and whisk it northeast.

Bottom line: Keep watching in Texas but there’s some meteorological support to believe this isn’t our storm.

Elsewhere

The remnants of Gordon have a 30 percent chance to develop over the next week. Another disturbance to the east of there also does, but neither is a threat to land.

There is growing model support for an African wave to develop near the Cabo Verde Islands next weekend, but it too seems destined to go out to sea. Right now, almost all our attention is fixated on the Caribbean.

With Caribbean development several days out, how should we be assessing things?

Headlines

  • Today’s post shows how modeling is struggling to handle what may or may not happen in the Caribbean next week.
  • At this point, we expect tropical development, but where that goes, at what intensity, and at what speed are all open questions we cannot currently answer.

Caribbean confidence levels low

Rather than go into a post where I go back and forth on hypotheticals regarding potential Caribbean development next week, I want to go into how we should be thinking about this, sitting here on Wednesday, September 18th. First, the easy part: The National Hurricane Center has given the northwest Caribbean about a 20 percent chance of tropical development over the next week.

(NOAA NHC)

You may be asking why this seems so low. The NHC operates fairly conservatively, so expect these odds to probably increase as we get closer. After all, it’s not a given that we’re going to see tropical development in the northwest Caribbean. It’s a possibility.

During Hurricane Beryl and again during Francine, we noted how good the European AI model and ICON model handled the storms. They were consistent on track and fairly consistent on the idea of intensity, particularly in the 5 days ahead of landfall, while other models were still generally bouncing around. So why can’t we just use those models and get a good idea of what may occur here? Well, here are the last 8 runs of the European AIFS model valid for next Sunday morning.

The European AIFS model has been consistent in showing tropical development next week, but it has been literally all over the map in terms of where and how fast it takes the storm. (Tropical Tidbits)

If you look at the GFS or ICON or whoever else you want, you would see a similar outcome. None of the operational modeling has any consistency or clue with respect to this system, short of “something might happen somewhere.” So when we tell you to ignore and disregard people posting single run deterministic models on social media saying “not a forecast, but check this out!” this is what we mean.

So the next thing you may ask is, “Matt, you’re a meteorologist. Isn’t it your job to cut through this and tell me what might happen?” And the answer is yes. However, I know my limits. When I look at GFS and European ensemble guidance, the traditional physics-based ensembles I see similar type outcomes with a wide berth of possibilities. Some go northwest, some go northeast, some don’t even develop it at all.

The GFS ensemble spaghetti plot of low pressure systems across the Gulf from the northwest Caribbean disturbance, valid through next Friday night, showing little to no strong signal in the noise. (Weathernerds.org)

Finding signal in the noise is my job, and right now the only signal I maybe see is a propensity for the majority of model guidance to go north or northeast with this. And even that is sketchy at best. But it tells me Florida absolutely needs to watch this closely. And since we’re more than a week out from any impacts, that’s probably good enough.

The goal of a meteorologist this far in advance is not to get the call spot on. Anyone can try to do that, and periodically they’ll nail it while also likely delivering 65 other false alarms in the process. The goal of the meteorologist is to tell the audience what we know. We could dive deeper into the upper air pattern or things like that, but I feel we’re still a couple days away from getting too fancy with explaining how that impacts this outcome. But I’m not cherry picking model runs or data. I’m showing you examples of erratic deterministic output, which is all we have right now, and I’m showing you examples of slightly more stable though no less uncertain ensemble data. It’s a lot of noise, so don’t be panicked by individual cherry picked runs.

The bottom line right now? We have no idea what will form, exactly where it will form, and where it will go. But we are fairly confident that something is going to develop in the northwest Caribbean next week.

We’ll keep it simple today and leave it there.