A delicate ballet will unfold in the southwest Atlantic over the next several days but the choreography is far from determined

In brief: As Gabrielle heads out to sea and toward the Azores, we’ll begin to pay close attention to two newly minted Invests, 93L and 94L in the southwest Atlantic. The whole pattern bears watching for the East Coast over the next week or so. But uncertainty is extremely high, with a lot happening over a small area and any one feature having impacts on the others. We explain the delicate ballet unfolding today.

Major Hurricane Gabrielle

(NOAA/NHC)

We’ll be quick on this one. Gabrielle intensified into a category 4 storm with 140 mph winds. The storm has probably peaked in intensity now and is going to move eastward out to sea.

Gabrielle is a very classic looking Atlantic hurricane as it begins to move out to sea. (Tropical Tidbits)

The next questions for Gabrielle are how it will impact the Azores and if it can make it to Europe. Gabrielle should remain a fairly formidable, albeit less intense storm as it moves near the Azores on Thursday or Friday. More details to come on that. It’s still a bit too soon to say how it will impact Europe, but it’s possible a remnant low approaches Portugal by early next week. In the near-term, interests in the Azores should be monitoring Gabrielle’s progress.

Atlantic Invests

The two disturbances we’re watching in the Atlantic are less than 1,000 miles apart, and both look fairly healthy this morning. (Weathernerds.org)

The area in the Atlantic with higher development odds right now is Invest 93L. This trailing disturbance has a 90% chance of development. Invest 93L has a similar look and feel to Gabrielle right now, and the models are indeed latching onto a higher chance that this develops by Thursday. Invest 94L will be moving into the Caribbean over the next couple days, so it’s likely that land interaction will inhibit its development. By Thursday morning, we expect to see 93L northeast of the islands and probably on the way to becoming a tropical depression. Invest 94L should be in the Turks and Caicos Islands or near Hispaniola as a tropical wave/disturbance.

Google AI and European ensemble model forecast locations of the two invests on Thursday morning (Google Weather Lab)

Up to this point, the forecast should be rather straightforward. Beyond this point?

There are about a million things that could happen after Thursday or Friday. The complicating factors right now include a.) What happens to 94L in the islands? That will help determine how far west it can get before being tugged north. b.) How strong does 93L get and how fast? That could help determine where it’s placed relative to 94L by the weekend which could influence both the track and development of 94L; they are fairly close together after all. c.) What about the trough in the Southeast? Will it be progressive enough to try to “capture” 94L and pull it into the Southeast or Mid-Atlantic? Or will it leave 94L stuck between a rock and a hard place with little opportunity to maneuver?

The upper air pattern in the southwest Atlantic is an utter mess this weekend, which means forecast uncertainty increases dramatically. (Tropical Tidbits)

The bottom line in all this is that there is a *lot* of uncertainty in the pattern this weekend. Inject two possible tropical systems into the mess, with all these players residing over less than 1,500 miles of distance and you have a recipe for extreme uncertainty. As the Southeast trough exits, it could theoretically “capture” the disturbance and pull it more north or north-northwest toward the Southeast or Mid-Atlantic coastline by Sunday or Monday. Or later. And I think that’s where much of the concern sits right now in terms of land impact. It’s one of several possible outcomes. Folks on the East Coast from Florida through New England should monitor the progress of these systems in the next few days to see if we can pull a signal out of this. Because right now, we can’t.

A spaghetti plot of Google AI ensembles shows a “choose your own adventure” outcome by early to mid-next week. (Weathernerds.org)

Bottom line: No one has any idea what these are going to do, and all you can do at this point is monitor the forecast and make sure you check on your hurricane plans and kits on the East Coast.

In the very near-term, Invest 94L will bring heavy rain to Puerto Rico and the Virgin Islands today.

(NWS San Juan)

Localized flooding is a possibility in the heaviest rains. This will continue tomorrow and Thursday as well, easing up by Friday and Saturday.

Atlantic Tropics shifting into a potential busier mode over the next 10 days

In brief: Gabrielle became a hurricane and then a major hurricane overnight and this morning. It should head out to sea now, but it may bring some impacts to the Azores or even Europe eventually. Disturbance 1 from the NHC carries a 70% chance of development and is currently not a serious land threat. Disturbance 2 from the NHC carries a 40% chance of development and has a high degree of uncertainty in its forecast heading toward the weekend. We explain it all below.

Things have escalated a bit in the tropics, but there are still more questions than answers in some cases. Let’s walk through the development areas and explain what we know in each case.

Major Hurricane Gabrielle

(NOAA/NHC)

Last week we were scoffing at how paltry Gabrielle looked. But we said despite that it had a chance to become a hurricane, if not a major hurricane by Sunday or Monday. Well, here we are, and we got our major hurricane. Gabrielle has maximum sustained winds of 120 mph this morning, and it looks spectacular.

A static satellite image of Gabrielle this morning shows a well-organized storm with ample thunderstorms around its eye. (Tropical Tidbits)

Gabrielle is in a bit of a precarious position, as it moves over much warmer than normal water. The water will be gradually cooling, however as it moves north and northeast. Still, Gabrielle has a good 24 hours in a favorable environment, and we could see it take a quick run at category 4 intensity this afternoon before peaking. From here, Gabrielle strolls out to sea and slowly weakens.

That said, Gabrielle probably won’t fizzle out. Impacts from Gabrielle are possible in the Azores by Friday and perhaps even in Iberia by Sunday or Monday. Exactly what those impacts will be are TBD. Uncertainty in the forecast from the Azores to Europe increases with time in Gabrielle’s forecast.

70% chance of development area

I want to preface this by saying that there are two distinct disturbances in the Atlantic, and the models are still sorting things out with each one. For now, I’m going to focus on the Central Atlantic one discussed here as the most likely to develop and also farthest east. A tropical wave in the central Atlantic is carrying a 70 percent chance of development over the next week as it comes west and northwest.

The next wave to watch will move north of the islands later this week. (NOAA NHC)

This system will be interesting, though I’m not particularly concerned about it making landfall right now. That said, it bears some watching. We’re still several days away from it getting north of the islands and south of Bermuda. But when it gets to that area, the upper level pattern is supportive of a system that moves slowly, possibly even stalling out. High pressure will block its exit east, at least initially, and a trough over the Southeast will sort of inhibit westward movement.

Upper-level pattern supports a system slowing or stalling south of Bermuda and north of the Caribbean islands by the weekend. (Tropical Tidbits)

On the one hand, the high is expected to eventually weaken enough to allow for an exit out to sea, possibly by Tuesday or Wednesday of next week. On the other hand, systems that stall out inherently have high uncertainty and bear watching. If one of the puzzle pieces currently in place in the forecast ends up shifting, the overall outcome could also shift. For now, I would say continue to monitor this system, but it’s probably not worth losing sleep over at this very moment.

40% chance of development area

And then ahead of the above discussed area, we have another area to watch. This one is carrying a 40 percent chance of development over the next week.

The third system is a disturbance with a 40 percent chance of development over the next week. (NOAA NHC)

Looking on satellite, both the previously discussed disturbance and the leading one look fairly healthy. The trailing the disturbance is in a slightly better environment, hence the better odds right now.

Satellite imagery of two NHC identified areas of interest in the Atlantic. (Weathernerds.org)

The leading disturbance discussed here will probably track off to the northwest, staying fairly low-end over the next 2 to 3 days. In fact, by Thursday, 1 Google Deep Mind ensemble member develops this area, while about half develop the trailing wave with higher odds. This disturbance has to deal with a bit more shear and also Gabrielle’s wake a little more. However, by Saturday evening, a little under half of the Google ensembles develop this disturbance near or just east of the Bahamas.

A number of Google AI ensemble members develop the 2nd disturbance by Saturday night in some fashion near or just east of the Bahamas. (Weathernerds.org)

Notably, about the same percentage of European ensemble members are doing the same thing here. So there is growing model support for something in this area in about 6 days. What it looks like, what it is, what its impacts will be? We don’t know yet. But interests in the Bahamas and Turks and Caicos Islands should be monitoring the progression of the NHC Disturbance 2 over the coming days. For the U.S. Southeast? It’s too soon to say much about this. Folks in Florida up through the Carolinas should continue to monitor but understand that there is a very high amount of uncertainty with this wave. Confidence in Disturbance 1 is a bit higher both in track and in details right now. Confidence in this Disturbance 2 would be classified as low to lower than average. More to come.

Gabrielle in line to become a hurricane as it turns out to sea while the U.S. sees a wetter pattern change this week

In brief: Gabrielle should become a hurricane by tomorrow as it passes well east of Bermuda and out to sea. Behind Gabrielle, the next tropical wave may develop heading into late next week. But aside from that, it looks pretty quiet, with AI models backing off Caribbean and southwest Atlantic development. A wetter pattern takes hold in many drought-plagued parts of the country, except New England, as mild/warm weather continues.

Tropical Storm Gabrielle

(NOAA/NHC)

Gabrielle will be passing east of Bermuda today and tomorrow, thankfully, as it likely becomes a hurricane. Winds are currently 65 mph, and it’s looking like it is on the cusp of becoming a hurricane.

Satellite loop centered on Gabrielle shows it trying to organize toward hurricane intensity. (Tropical Tidbits)

Gabrielle is expected to intensify, possibly rapidly over the next 48 hours, and there is a better than usual chance that it could become a major hurricane in that time. Odds of rapid intensification are around 2 to 3 times climatology, which is to say better than usual.

There is pretty good agreement on the track forecast of Gabrielle. It will slowly creep northward over the next 36 hours before making a bit of a hard right out to sea.

Minimal deviation in track overall between models with Gabrielle, and its remnants could eventually make it to the Azores. (Tropical Tidbits)

Other than a potential brush with the Azores in 5 days, Gabrielle will be just something to look at through midweek.

Behind and beyond Gabrielle

The next wave up has seen some growing potential for development. Odds went from 20 percent the last couple days to 40 percent this morning.

An area in the eastern Atlantic has about 40 percent development odds as of Sunday morning. (NOAA/NHC)

At least initially, this seems to be dealing with the same issues that plagued Gabrielle early on. Dry air and wind shear are limiting any organization.

Dry air and wind shear are limiting any real development of the tropical disturbance west southwest of the Cabo Verde Islands. (Weathernerds.org)

So I would not expect much of this through at least Tuesday or so. Beyond that, conditions are expected to become more favorable. In general, I think this will take a similar track to Gabrielle, but it may creep a little farther west than the current storm is doing.

Google’s suite of AI models has backed off Caribbean and SW Atlantic development a bit, choosing to focus on the next wave instead. (Google Deep Mind)

Last week we discussed the AI models and how they were all a bit more bullish than traditional weather modeling on potential northwest Caribbean and southwest Atlantic development. Well, it seems that they have chosen instead to focus more on the upcoming wave rather than that more dangerous area closer to land. You can see the change in the forecast from Friday to today above for next Sunday.

In general, the pattern through next weekend will continue to favor this offshore track of anything tropical in nature. For now, the U.S. is mostly protected from anything on the Atlantic side. And with no real sign of anything imminent in the Caribbean or Gulf, we look good through the end of September.

The upper air pattern supports any tropical mischief staying offshore and away from the U.S. through the end of September. (Tropical Tidbits)

Perhaps the Gulf or southwest Atlantic will get more active in early October, but that’s extremely speculative.

That trough in the upper atmosphere over the Southeast above (blue) indicates that weather will be pretty unsettled over the next several days as well. We should begin to see locally heavy rainfall tomorrow through midweek from the Ozarks into the Ohio Valley. These are areas that are currently under drought conditions, so this will be mostly welcome news. However, the driest parts of New England may not cash in quite that much from this week’s weather, with a growing severe drought from Vermont through Maine. This is impacting foliage season, as my friend Jim Salge reports.

Rainfall over the next 7 days will be highest from the Ozarks into the Ohio Valley, areas that are currently in drought. (Pivotal Weather)

With the heaviest rains, we may begin to see some flooding issues crop up.

For those of you looking for true, legitimate fall weather, particularly in the southern half of the country, you may need to keep waiting. At times, some frosts may be possible in the usual northern colder spots that typically turn that direction this time of year. But the forecast for days 8 to 14 continue to show good odds of above normal temperatures across the entire country.

Above normal temperatures are expected to dominate the end of September and beginning of October. (Pivotal Weather)

But if we can keep any hurricanes away, perhaps it’s not such a bad trade off.

Gabrielle is doing well today, on the road to intensification in the open Atlantic

In brief: Gabrielle is looking better this morning, as it begins to slowly develop and organize in the open Atlantic. It should pass east of Bermuda but still bears some watching. Plus, today we dig in on the Caribbean battle in about 10 days between AI models and traditional weather models.

Tropical Storm Gabrielle

(NOAA/NHC)

Compared to yesterday at this time, Gabrielle looks phenomenal. It seems to have fought off most of the serious dry air issues. Now, it’s dealing with some lingering shear. So it’s still a bit “blobby” in nature, but that area of significant thunderstorms just east of the center has been persistent, usually a sign that a storm is trying to get better organized.

Gabrielle’s thunderstorms are much more persistent today than they have been. (Tropical Tidbits)

When you look at the satellite loop above, I mean, you can still very clearly see the wind shear issues it is putting up with. But that shear is expected to slowly ramp down as Gabrielle finds its way northwest over the next couple days. This should lead to organization and intensification, and Gabrielle is forecast to become a hurricane by Sunday. There is a slight chance that Gabrielle may even make a run toward major hurricane intensity by late Sunday or Monday. In fact, SHIPS model guidance is over 4 times higher than climatology for rapid intensification of a 75 mph wind increase to occur over the next 72 hours. We’ve seen higher odds before, but that’s still rather healthy, all things considered.

In terms of track, the NHC track is close in line with the vast majority of model guidance that currently keeps the storm east of Bermuda. You should still be monitoring this system if you have interests in Bermuda. But right now, it does appear to be a swing just east. More to come on this.

Elsewhere

The wave behind Gabrielle with 20 percent development odds is of minimal interest right now. What is more interesting is this battle that’s playing out between AI modeling and classic, physics-based modeling for next weekend and beyond in the northwest Caribbean. If you look at the two model ensembles (Google Deep Mind vs. the European ensemble), you can see a clear deviation in excitement around September 29th.

AI modeling (left) is far more enthusiastic about tropical development in the northwest Caribbean to close September than is European ensemble modeling (right). (Weathernerds.org)

The AI model suite is very, very excited about potential development in the northwest Caribbean to close September. I show Google Deep Mind above, but if you look at other AI modeling, including the European AIFS ensemble, you get a similar pulse of enthusiasm. Traditional, physics-based models are not as enamored with this setup and keep any developments confined to a couple rogue ensemble members.

I will say, if AI modeling has had a bit of a mixed bag of results this summer, it has come with “genesis” forecasts like this; where you can’t quite determine the specific disturbance that will develop but the models are very excited. They have had some moments, but they have also had a rather high genesis false alarm rate. Climatology changes in late September and October, and this is a favored area to watch, so from that point of view, you have to at least consider it may be seeing something. Or perhaps it’s a little too overzealous based on history, which is the bread and butter of AI modeling and wants to get things started with a bang. For now, this is not really an area to worry about or even monitor closely. But it’s an area we’ll be watching, and we’ll be very curious to see how the AI tools handle this as verification rolls forward.

Going to leave it there today. More to come this weekend!