Matt Lanza

Potential Tropical Cyclone 9 looking like it’s going to be a serious rainstorm for the eastern Carolinas

September 26, 2025 at 7:00 pmSeptember 26, 2025 at 7:00 pm by Matt Lanza

In brief: Invest 94L was reclassified as Potential Tropical Cyclone 9, meaning it is likely to become a tropical storm within the next 24 to 36 hours and produce tropical storm conditions in the Bahamas. We discuss the rain risks there and in Cuba. We also take a closer look at the current forecast goalposts of rainfall for coastal South and North Carolina.

We wanted to add a post this evening to highlight that Invest 94L has been designated as Potential Tropical Cyclone 9, meaning that the National Hurricane Center expects it to develop within the next 36 to 48 hours, requiring tropical storm watches and warnings. In this case, those warnings are presently limited to the Bahamas.

5PM ET Advisory for PTC 9, soon to be Imelda. (NOAA/NHC)

PTC 9 is expected to become a tropical depression tomorrow and a tropical storm tomorrow night as it moves into the Bahamas. Heavy rain is likely in the Bahamas, along with increasing winds and seas as the storm moves through.

Total rainfall of 4 to 8 inches is expected across much of the Bahamas, with isolated much higher amounts over the eastern tip of Cuba. (NOAA WPC)

Some intense rain is likely over the eastern tip of Cuba as well. Rain totals may reach as high as 16″ or more in the higher terrain there leading to dangerous flooding and landslide risks.

From there, you can see the National Hurricane Center track above. It shows a hurricane and eventually a tropical storm approaching the coast of South Carolina by Tuesday night or Wednesday. There is a tremendous amount of uncertainty on exactly where this system will go, and if you look under the hood and read the NHC’s discussion, they make this clear as well. It’s possible that a landfalling hurricane or tropical storm hits the South Carolina or North Carolina coast early to mid-next week. It’s also possible that this thing just taps the brakes and meanders offshore for a few days. Both scenarios deliver impacts, including torrential rain to the Carolinas, particularly in the Coastal Plain between the Lowcountry, Pee Dee and southeastern North Carolina.

Rainfall scenarios

So let’s lay out a couple of the rainfall scenarios. First, here’s the current official forecast. Consider this the best estimate of how much rain may fall, on average, across the region over the next 7 days.

The official WPC forecast from NOAA for the next 7 days, showing anywhere from 4 to 8 inches of rain over a wide area of the coastal plains in the Carolinas, extending into the Piedmont and parts of Virginia as well. (Pivotal Weather/NOAA WPC)

So, officially at least, the current thought is 4 to 8 inches with isolated higher amounts at the coast.

Let’s say the system never really makes landfall and approaches the coast but probably stays offshore and drifts eastward. The GFS model shows this fairly well today. Its rainfall totals are still impressive.

The GFS model from late this afternoon shows the heaviest rain primarily on the South Carolina coast, with 4 to 8 inches in the Charleston area and lesser amounts north of there. (Pivotal Weather)

But they’re also notably lower than the current official forecast. This feels like a nice “floor” for how much rain could occur. I would anticipate at least this much. There will obviously be ways this could change, but given the scenarios in play, that’s where we are right now.

Now, let’s say the storm comes ashore or just hugs the immediate coast for a couple days. This is sort of what the European model showed this morning. How much rain falls in that scenario?

European model rainfall forecasts are much worse than the current outlook or the GFS forecast due to the storm sitting on the coast for a couple days. (Pivotal Weather)

Well, the Euro represents an extreme example at the moment but one that cannot be entirely ruled out. In this scenario, rain totals of 20 inches would be possible on the coast between Charleston and Wilmington with a wide area of 5 to 15 inches in the Pee Dee and southeastern North Carolina. This would bear some similarities to Matthew or Florence in that scenario in terms of the rainfall. Both of those storms were terrible flood producers in this region. To be clear, no one is forecasting a Matthew or Florence redux. But on the higher end of the spectrum of realistic possibilities, we can’t adequately rule the Euro model’s scenario out yet. Same goes for the less problematic GFS, of course.

But in addition to the “there’s a storm coming” mindset, we want folks on the coast and inland in the coastal plain to prepare for the potential for a long-duration rain event and the potential for flooding as well. There will be much to monitor this weekend, and we’ll be back in the morning with the latest.

Invest 94L remains worth watching for the East Coast, while Gabrielle slams the Azores tonight

September 25, 2025 at 9:00 amSeptember 25, 2025 at 9:00 am by Matt Lanza

In brief: Invest 94L’s forecast is no clearer today, but we have a couple things to discuss related to it. It remains worth watching closely on the East Coast. Meanwhile, Humberto is now expected to become a major hurricane while passing southwest of Bermuda. Then we have Gabrielle which will impact the Azores with hurricane conditions tonight and make a brush with Portugal and Spain later this weekend.

Invest 94L

We’ll get to the named storms shortly, but let’s take stock of Invest 94L this morning.

Right now, the Invest is not terribly well organized, though it does give off a rather healthy-looking appearance. The surface “center” is presumed to be somewhere just north of Hispaniola, while thunderstorm activity is displaced mainly south and east of there, closer to a mid-level low pressure. So, we continue to see everything related to 94L right now looking rather disjointed.

As the wave moves into the Bahamas, it will encounter a slightly more hospitable environment to begin to try and organize. This probably won’t occur until late tomorrow or Saturday. If we see organization, it will probably begin later Saturday or Sunday.

The forecast location of 94L on Sunday evening ranges from just north of Cuba to all the way at the northern tip of the Bahamas. (Weathernerds.org)

By the time we get to Sunday evening, we actually have some growing model agreement in the general track of 94L, which is to say it will track off to the north-northwest. However, there is a massive difference in where along that path Invest 94L will be. Some European and GFS ensemble members have it passing just off the North Carolina coast. Others keep it locked up down near Cuba. There is some cross-track spread and a lot of along-track spread. The Google AI look above represents a happy medium of everything right now I think. And you can see how uncertain the placement is. This is important because where it sits and how close to Humberto it is will have implications on future track.

A combination of all the traditional physics-based ensembles shows a pretty good consensus on track for 94L up to about 30°N latitude. Thereafter, it gets unruly. (Polarwx.com, Tomer Burg)

But in general, I think what we’ve seen since yesterday is probably a slightly riskier track for the East Coast, as the model guidance has trended a little to the west. Of course, Humberto’s track has also trended a bit farther west too. Confidence remains low, and most of what I would say beyond Sunday is just rampant speculation at this point.

Bottom line: Continue to monitor Invest 94L if you live on the East Coast, particularly in the Carolinas and Virginia. But we have a long, long way to go.

Heavy rain seems likely regardless in the Carolinas and Virginia. We’ll continue to update that into the weekend.

Tropical Storm Humberto

Humberto’s forecast track and intensity, showing it becoming a major hurricane by Sunday evening. (Polarwx.com/Tomer Burg)

Humberto is getting its act together this morning. Slow strengthening is expected to continue, and Humberto should become a strong tropical storm by tomorrow morning and a hurricane by Saturday. The track of Humberto takes it over some of the warmest water in the southwest Atlantic outside the Caribbean islands, so it will have a good deal of energy to work with.

Humberto’s trend over the last 8 to 10 hours has been to get a bit better organized with a big blow up of thunderstorms near the center. (Cyclonicwx.com)

Humberto will remain well offshore, but the question becomes whether or not it will impact Bermuda. As of now, with the westerly trends we’ve seen since yesterday, this appears to build confidence that Humberto should remain to the west of Bermuda. However, depending on its size and intensity, some degree of direct storm impacts are possible in Bermuda as it passes. But it’s too soon to say anything with much confidence. We’ll also see how much intensity Humberto can gain in the next 72 hours. SHIPS model guidance shows a 2 to 3 times greater than climatology chance of rapid intensification, slightly lower odds than we saw with Gabrielle but still a bit higher than is typical. We’ll watch through the weekend.

Hurricane Gabrielle

Gabrielle is still a hurricane this morning, though it is clearly interacting with colder water, causing it to lose a bit of steam.

Despite this, Gabrielle is an imminent threat to the Azores, and hurricane warnings are posted there. If you look closely at the European model forecast of winds today through tomorrow, you can see how Gabrielle weakens in the near-term but then fires back up hurricane-force winds (red) as it crosses the Azores tonight and early tomorrow.

Gabrielle will ramp back up tonight as it begins to transition to an extratropical storm with some help from the jet stream. (Weathernerds.org)

This extratropical transition process can be deceptive. In theory, the storm is losing hurricane characteristics, but often times, that transition to a more jet stream dominated storm rather than a tropical/warm water dominated storm can lead to a burst of intensification. Think about Hurricane Sandy in 2012. That was technically no longer a hurricane, but a potent jet stream made it behave identically to one. Same goes for the Azores tonight; Gabrielle will be making that transition, but the impacts on the ground will be the same: Hurricane-force winds, rough seas, heavy rain, and surge.

From the Azores, Gabrielle will continue to track toward Europe, where it shall retire in leisure. Let’s extend that wind forecast above out through the weekend.

Gabrielle’s remnants will likely approach Portugal at low-end tropical storm or tropical depression intensity before it falls apart completely near or in the Gulf of Cadiz. (Weathernerds.org)

You can see that Gabrielle’s tropical storm force wind field (in green) disintegrates as it approaches Portugal. Thus, we don’t expect tropical storm impacts in Europe. We could still see some heavy rain or gusty winds and rough seas, particularly in southern Portugal. Current European model forecasts call for about 15 to 30 mm of rain (0.6-1.1″) in parts of southern Portugal and southwest Spain.

Rainfall on the order of 15 to 30 mm with perhaps some higher amounts will be possible through early next week in Portugal and southwest Spain. (Pivotal Weather)

Rain would be most welcome in northern Portugal, which is in significant drought at the moment.

Wednesday evening update: Humberto cast as lead actor with the dueling southwest Atlantic disturbances

September 24, 2025 at 6:32 pmSeptember 24, 2025 at 6:32 pm by Matt Lanza

In brief: Invest 93L was upgraded to Tropical Storm Humberto this afternoon, and it is not currently expected to threaten land. Invest 94L’s forecast remains directly related to Humberto and has a very high degree of uncertainty. This will continue to be a low-predictability situation for another couple days at least.

I think this is the first time all hurricane season we’ve done two posts in a day? We’ll call that a win. Anyway, this will be brief, but I want to catch you up on some changes today.

93L is now Humberto

Humberto will move and strengthen quite slowly over the next few days before perhaps threatening to become a major hurricane by early next week. (NOAA/NHC)

In a case of again dispensing with formalities, we took Invest 93L and skipped the tropical depression status and jumped right to tropical storm classification. Tropical Storm Humberto has winds of 40 mph. It’s certainly not the worst looking tropical storm we’ve ever seen.

Tropical Storm Humberto slowly gathering itself northeast of the Islands. (Weathernerds.org)

Thankfully most land will not likely need to worry about Humberto. However, interests in Bermuda should continue to monitor this storm’s progress. Various tropical models and most ensemble guidance curves Humberto on a trajectory similar to Erin earlier this summer, which would keep it west of Bermuda. However, depending on how well organized the system is, it could produce some meaningful impacts by early next week in Bermuda. Stay tuned.

Invest 94L

Meanwhile, the one we’re watching a little more closely, Invest 94L remains in the Caribbean. It was initialized this afternoon very near the southwest tip of Puerto Rico.

But you can see that there are clusters of thunderstorms both north and south of the island. The system is quite strung out at the moment. While the surface reflection may be near Puerto Rico, there is clearly some sort of mid-level and upper-level reflection elsewhere. You’d like to see a system better vertically stacked before it can organize, but at this moment in time, 94L is anything but that. So, don’t expect this to pull a Humberto we wouldn’t think.

We have a good 2 to 3 days before this clears Hispaniola and makes it into the Bahamas. At that point, assuming it is not shredded by the mountains of Hispaniola, we would likely begin to see an environment more conducive to organization. Much like this morning, the frustrating reality is that we have no real clue what happens next. The operational model guidance is definitely dropping options though.

The GFS seems to favor a Fujiwhara interaction between 94L and Humberto, which would potentially pull 94L toward Humberto and pull Humberto a little farther west (offshore of the East Coast) before it all heads out to sea.

You can see how Humberto basically pulls the weaker 94L into its orbit on the GFS model, a scenario that while plausible isn’t any more likely than other scenarios. (Weathernerds.org)

This scenario is a realistic one for sure, but I’m not sure it’s any more likely than other possible scenarios. The European model basically leaves 94L behind once Humberto heads out to sea and does weird things with it, which again is plausible but not necessarily likely. Other options include literally nothing, a storm going up the East Coast, or just a storm that follows Humberto out to sea. Put all that together, and we’re still very much in “choose your own adventure” mode with regard to 94L’s future. Stay tuned, but I don’t expect much clarity on this for at least another day or two.

Notably, regardless of what transpires here, there will begin to be some heavy rain risk in the Carolinas and Virginia in about 3 or 4 days. After Helene last year, I know this won’t give people warm and fuzzies, but just bear in mind that this is a much different scenario than Helene from an entirely different direction. Certainly, keep tuned to the forecast, particularly near the coast, but we just want to offer a little reassurance that anything remotely like that is not currently in the cards on any model guidance.

The rainfall forecast over the next week calls for 1 to 3 inches, with isolated 4-to-5-inch totals in eastern Virginia and interior North Carolina, east of the mountains. (Pivotal Weather)

Rain totals of 1 to 4 inches are broadly forecast across Virginia and North Carolina down to about Columbia, SC over the next week. Notably, this is east of the mountains.

More tomorrow.

Twin tropical waves continue to bear watching in the coming days in the southwest Atlantic

September 24, 2025 at 8:29 amSeptember 24, 2025 at 8:29 am by Matt Lanza

In brief: The Atlantic Invests 93L and 94L will continue giving forecasters fits in the coming days as their proximity to one another, their sensitivity to how well organized one or the other gets, and their proximity to land will play a role in everything that ultimately happens. With so many moving parts, it’s tough to define a narrative of potential outcomes right now, so we walk through what we know and more importantly what we do not.

Twin Invests 93L and 94L

Both Invest 93L and 94L have high chances of developing in the coming days. And the situation has grown no less complicated.

Both invests look less well organized than they did 24 hours ago. (Weathernerds.org)

The first thing I can say with some confidence about all this is that we are looking at a somewhat lengthy process here. We may be watching these systems for the next week. While Invest 93L seems likely to not be a land threat (though it could tease Bermuda), it may ultimately help influence Invest 94L, which could be a land threat on the Southeast or Mid-Atlantic coasts.

Invest 93L

First off, Invest 93L is the better looking of the two this morning, and all along it has been the more likely of the two to develop. Still, we’re not there yet. It seems 93L is dealing with the broader circulation on the backside of Gabrielle, as well as a pocket of wind shear impinging on its southwest flank. It’s just not in an optimal location at this particular moment, so we’re probably still a day or two away from this getting together into something more formal.

Both the European ensemble suite and AI modeling supports 93L sitting somewhere a few hundred miles north of the Caribbean islands on Saturday evening, probably beginning to strengthen. (Weathernerds.org)

So that’s in about 84 hours. Beyond this point, the general idea is that 93L should continue off to the northwest before turning northward near or southwest of Bermuda. The only real unanswered question with 93L is whether it ultimately threatens Bermuda. Models keep it southwest of the island, so depending on how well developed, how strong, and how close it comes to the island will determine how significant the impacts are. Suffice to say, interests in Bermuda should monitor the progress of 93L.

Invest 94L

Meanwhile, the same cannot be said about Invest 94L. There is virtually nothing we really can say about Invest 94L with any strong confidence one way or another. The spread by Sunday morning in ensemble members with 94L is much wider and the intensity is a good deal lower than 93L at that point. So there is going to inherently be more uncertainty on location because it will probably be a somewhat sloppy system.

The potential location of 94L’s center is much more uncertain than 93L on Sunday morning, and the intensity is likely still on the lower-end. Confidence in any specific forecast outcome is very low. (Google Weather Lab)

In theory, the track of Invest 94L should be more longitudinal in nature by the time we get to Sunday or Monday. Low pressure over Appalachia, high pressure near Bermuda, and a general south to north upper air pattern would theoretically allow 94L to track north or north-northwest by then. But this is partially where Invest 93L’s potential input on this outcome begins to come into play. If 93L is well-developed, it could force 94L to remain buried in the Bahamas for a couple days, could force it to remain weak, or it could even absorb it completely (the 00z GFS model showed this). If 93L struggles, then almost all bets are off.

By the time you get to midweek next week, there is just an enormous spread of possible outcomes with 94L.

Twinvestment advice

If you live in Bermuda, the Bahamas, or on the East Coast between Florida and New England, you will want to continue to follow this forecast each day. I really cannot emphasize enough how uncertain it is. When you get two systems like this close together, weird things can happen. Anything from a significant land impact to much ado about nothing remains in play. Stay tuned.

Hurricane Gabrielle

Elsewhere, Hurricane Gabrielle remains a major category 3 storm today as it tracks toward the Azores Islands, where a hurricane warning has been issued.

Gabrielle is expected to lose tropical characteristics as it moves through the Azores but it will bring hurricane-force winds to the islands. (Polarwx.com)

Gabrielle should cross through the islands tomorrow night delivering hurricane impacts. As it continues to move over cooler water, it will likely steadily weaken. That said, it will also get a jet stream “boost” as it passes the islands, allowing for hurricane-force winds to continue there. Hence the hurricane warnings. Gabrielle will fully lose tropical characteristics after it passes the Azores and approaches the Iberian Peninsula this weekend as a remnant low.

European model forecast for Sunday morning showing Gabrielle’s remnant hugging the coast of Portugal but tracking southeasterly. (Tropical Tidbits)

It will still be capable of bringing some gusty winds and rain to Portugal or Spain, but the current forecast track does keep the strongest conditions offshore right now, with the system tracking into the Gulf of Cadiz and near the Strait of Gibraltar. Still, probably something worth watching for Portugal at least! Rain would be welcome, especially in the northern half of Portugal which is experiencing a serious drought.