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.

A quiet balance of the week before Caribbean shenanigans next week

Headlines

  • After flooding and strong winds in North Carolina, we look at why PTC 8 never became Tropical Storm Helene.
  • Caribbean mischief is likely next week with details TBD. But it’s clear something is probably going to try and develop.

How does an unnamed storm behave so much like a tropical storm?

Cleanup is underway in North Carolina after yesterday’s deluge from an unnamed potential tropical cyclone. We’ve gotten some questions as to how a storm with very obvious tropical storm conditions goes unnamed? Well, the point of the “Potential Tropical Cyclone” designation is to account for the fact that a certain system may not meet the technical requirements to be classified as tropical in nature or, alternatively, it may be close enough to land and unformed yet that it requires watches and warnings. The Carolinas needed watches and warnings for sure yesterday, and thus the PTC designation met the former definition that it fell short on account of technicalities.

PTC 8 analyzed on a surface map yesterday afternoon with a stationary front to its east and cold front to its south, which is indicative of a storm that is non-tropical in nature. (NOAA WPC)

In this specific case, PTC 8 was a cyclone, but it was not tropical in nature. It had fronts nearby, a rather clear designation of a non-tropical storm. This was more akin to a nor’easter type storm that we frequently see in the fall, winter, and spring months on the East Coast. Still, the impacts were virtually identical to a tropical storm and to most people that is likely what they assume they were hit with yesterday in North Carolina. The PTC products work in that respect as intended. However, there is still some inherent clunkiness in communicating the situation, which is why we tend to focus almost exclusively on impacts. For PTC 8, we had noted even late last week that this was going to probably be a rain and windmaker for the Carolinas, and even though the coverage of total rainfall was a bit surprising, for the most part this played out as expected.

Rain totals and radar estimates from yesterday’s rain in southeast North Carolina. (NWS Wilmington)

Rain totals were historic and exceptional across Brunswick County and portions of southern New Hanover County, NC. The gradient between Wilmington Airport (north of Wilmington) and Carolina Beach was remarkable. That’s about 16 inches difference over 16 miles. The isolated nature of some of these rain totals can really make a forecast tough. It’s just as plausible that this could have been closer to Wrightsville Beach than Carolina Beach. It’s just the nature of tropical systems.

Our thoughts are with the folks that were flooded yesterday that can hopefully clean up in a reasonable amount of time. We’ve seen a number of cases of extreme flooding this month: Myanmar, Europe, even parts of Manitoba, North Dakota, and Minnesota yesterday. All this is consistent with more extreme rainfall that is expected in a warming climate, though to what specific extent that is contributing is TBD. Most recently, August was the warmest recorded month in our historical record however.

Caribbean watch on for next week

We’ve been discussing reasons why we expect Atlantic activity to tick up to close September. The most specific example we have of this is what is expected in the Caribbean next week. We’re beginning to see operational models more frequently go a little crazy with development there. But it seems consistent across most operational models. The GFS, Euro, ICON, and AI modeling from ECMWF all show tropical development in the northwest Caribbean with various tracks west or north. There is no consistency in track, but there is consistency in development. This tells me that we’re likely to see something happen next week.

A strong signal on something developing in the NW Caribbean next week, but there are few specifics on details, which leaves uncertainty high. (Tropical Tidbits)

We see this on the GFS ensemble as well above, which shows a pretty healthy signal for development but also a significant spread in outcomes next Tuesday evening, with potential low pressure centers anywhere from Cuba to the Caribbean to the eastern Gulf of Mexico.

We have a lot of Texas and Louisiana readers here on the site since we’re based in Houston, so I want to make a quick comment about potential here. Right now, with a potential trough off the Southeast coast, no significant westerly steering component available, and the potential for a southward moving front in Texas or the Deep South, the most likely path of least resistance would probably be northward or northeastward.

Upper air pattern supports something likely to come broadly north or northeast out of the Caribbean next week. (Tropical Tidbits)

That’s not to say folks in Texas and Louisiana should ignore this; you should not. However, sitting here today, I’d be more likely to say the odds of impacts are greater in Florida than the rest of the Gulf Coast. We’ll see this sort of show itself a bit more in the coming days. Notably, given that this is developing off a Central American Gyre type circulation, there is historical precedent for high uncertainty in this setup, which is why I don’t want anyone to write this off yet. But I think Florida needs to watch this more closely than elsewhere, and I want to highlight that for our Florida readers.

Elsewhere, there may be a signal for a new disturbance off Africa to form later next week as well, but that’s days away from any land and is not a concern right now. Gordon has degenerated into an open wave in the Atlantic but could reform at some point this weekend or so. Still, it’s no threat to land. So for now, the only system to concern ourselves with will be next week in the Caribbean.

Potential Tropical Cyclone 8 dumping exceptional rainfall near Wilmington, NC

Headlines

  • Major flooding just south of Wilmington, NC has been occurring due to Potential Tropical Cyclone 8.
  • Additional rain and flooding, in addition to significant marine impacts and coastal impacts on the North Carolina coast are expected in the region through tonight as PTC 8 moves inland.
  • Gordon is a depression, but no other systems are noted in the Atlantic or off Africa right now.
  • We continue to see signs that the Caribbean will be the next place to watch next week, with potential development continuing to show up as noise in the forecast.

PTC 8 causing a ruckus in North Carolina

The good news is that Potential Tropical Cyclone 8 is running out of time to potentially become a tropical cyclone. The bad news is that it has been causing a lot of mischief in North Carolina since yesterday.

PTC 8 is running out of real estate before it comes ashore. (NOAA NHC)

Rain totals have been absurd in some parts of North Carolina, almost doubling forecast expectations for the week. The Wilmington, NC area has been especially hard hit with a bullseye of radar estimated rainfall near 20 inches just south of the city. The highest official total I can find is 15.25″ at Sunny Point, which aligns well with the scale below. There has been severe flooding in portions of Brunswick and New Hanover Counties, in North Carolina.

Ridiculous amounts of rain have fallen in southeastern North Carolina, focusing on the areas near Southport, Carolina Beach, and Wilmington. (NOAA MRMS)

Recurrence intervals appear to be over 200 to 250 years with this rainfall, making this an exceptional, historic event for this area.

Rain continues, though there may finally be some feeder band movement offshore that indicates a focus may shift out of Brunswick and New Hanover Counties and off to the northeast a bit. Those areas have seen comparably less rainfall.

Rainfall continues in southeastern North Carolina as PTC 8 approaches. Rains should settle down some after this afternoon though and the focus shifts inland. (Weathernerds.org)

Winds have been ripping as well, with gusts as high as 67 mph in Wrightsville Beach, 64 mph just south of there on Masonboro Island, and 60 mph in Wilmington. A 77 mph gust at Sunny Point south of Wilmington was taken a bit elevated, at 30 feet, so it may not be especially representative. But anyway, this is why we noted yesterday that whether it is or isn’t a tropical storm (it still isn’t technically) the impacts would be the same.

Not to be outdone, but winds and waves have been solid and high farther up the North Carolina coast with some damage to homes being reported as far north as Rodanthe on the Outer Banks. Beach erosion and ocean overwash is likely to continue into tonight across the North Carolina coast as PTC 8 moves inland. Coastal flooding of 1 to 3 feet is likely as well, with waves of 8 to 12 feet near the coast and to the north of Wrightsville Beach or so. Things will settle tomorrow.

In addition to all this mess, isolated tornadoes are a good bet in parts of eastern North Carolina.

Flood risk will move inland tonight, with totals of anywhere from 3 to 7 inches between the western North Carolina mountains, Charlotte, and into southeast North Carolina away from the coastal deluge. Higher amounts are likely in a few spots, especially near or south and east of Raleigh.

Rain totals of 3 to 7 inches are expected over a wide area of interior and southeast North Carolina. Higher amounts are likely. (NWS Raleigh)

Rains will become more scattered after today and tonight, and conditions will generally improve in North Carolina and the Mid-Atlantic after that.

Gordon downgraded, and no other Atlantic Ocean items to watch

Tropical Storm Gordon was downgraded to a depression, and it will continue to meander in the open ocean for a few days. There is a decent chance that Gordon will make another go at intensification later this week or weekend. Its future keeps it in the open ocean, the first true fish storm of 2024.

Gordon continues over the open ocean, no threat to land. (NOAA NHC)

Elsewhere in the Atlantic, conditions look quiet over the course of this week, and we do not expect any new systems of note to form. So we can spend most of the rest of the week waxing poetic on…

…The Caribbean

Yes, we continue to see signs that the Caribbean will be an area to watch in a week or so. We’ve started to see operational model runs begin to ramp up activity out of that area, though I strongly advise folks to disregard those one-offs, especially with regard to specifics. What do we know right now?

First off, we know that the overall atmosphere in the western Atlantic and Caribbean is going to become more hospitable to tropical development. After a period of hostile conditions that has basically been continuous since early August, the western Atlantic is going to flip to a more favorable background state for tropical development. In other words, less sinking air and more rising air will at least promote more development opportunities.

After weeks of sinking air in the background of the Atlantic, we see signs of a major flip after this week that could promote a busier period of tropical activity. (StormVista)

So the background state says that we should get moving. Second, we have seen signs in modeling of some type of either gyre scenario over Central America or the western Caribbean or some sort of disturbance that arrives there around early next week. This has been a feature in ensemble modeling for a while now, and it’s beginning to materialize in other modeling too as we get closer. But if you look at the GFS ensemble of sea-level pressures this coming Sunday, you can see a decent signal for low pressure in the northwest Caribbean.

A decent signal for low pressure in the northwest Caribbean next week may indicate that our next system is on the horizon. (Tropical Tidbits)

This isn’t a flashing red lights signal but it’s enough for me right now. I’ll be watching this area closely. Exactly what happens from here remains to be seen, but we know that the environment will become increasingly hospitable, and this is some of the warmest water in the basin. It absolutely merits paying attention in the days ahead, whether or not anything ultimately occurs.