Matt Lanza

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.

A Mid-Atlantic soaker as a coastal storm lurks off the East Coast

Headlines

  • Low pressure off the coast of the Carolinas will focus heavy rainfall this week, particularly in eastern North Carolina, along with some coastal flooding and rough seas.
  • Tropical Storm Gordon remains well out at sea, of no concern to anyone.
  • We continue to see hints that a system may make an effort to develop in the Caribbean after this week, but details remain elusive.

Carolina soaker

Low pressure and an associated trough off the coast of the Carolinas today is flinging rain back into southeastern North Carolina and the Myrtle Beach areas in South Carolina.

Low pressure sits offshore of South Carolina, and as it drifts northwestward, it will bring a dose of heavy rainfall to North Carolina in particular. (NOAA WPC)

This area of low pressure has an outside chance to form into a tropical entity before coming ashore in North or South Carolina tonight or tomorrow. Whether it does or does not, the impacts should be fairly well baked in right now, which is to say heavy rain, rough seas, some minor coastal flooding and erosion, and breezy conditions are likely in the Carolinas. Depending on the exact track of the storm, we’ll see where the heaviest rainfall sets up.

Rain totals of 3 to 7 inches are likely in eastern North Carolina and southeast Virginia, as well as in parts of the Blue Ridge this week. (Pivotal Weather)

Total rainfall should be highest in eastern North Carolina, where 3 to 7 inches is possible. There will also probably be a localized maximum of rainfall in the northern Blue Ridge in Virginia as well. A large area of moderate rain this week will surround all this from South Jersey into the Triad in North Carolina.

This system will linger onshore for a few days, so it only has about 18 to 24 hours left to formally develop if it does at all.

Deep tropics

Tropical Storm Gordon is likely to get downgraded to a depression soon. It may linger in the open Atlantic for a few days before it perhaps finds a more hospitable environment to reorganize later this week.

It’s the Gord*D*on’s fisherman. (NOAA NHC)

Either way, it will remain out at sea, no threat to land.

Behind Gordon, we have no concerns over the next week or so in the eastern Atlantic.

Caribbean watch

This week will be quiet in the Caribbean as well. However, there continue to be signs and signals that something may get going there after this week. It’s all conjecture at this point, but there’s enough there there to keep us at least paying attention in that region after this week. Not much else to say on this right now. More to come on this through the week though I am sure.