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!

Flash flooding risk in SoCal today, as the Atlantic continues to put on an exercise in futility

In brief: Gabrielle is struggling mightily this morning, with 50 mph winds but very little thunderstorm activity. It looks unlikely to threaten Bermuda but should still be watched. Not much else on the horizon. Locally heavy rain could produce flash flooding from southern California and southwest Arizona north into the Sierra today and tomorrow.

(NOAA/NHC)

Tropical Storm Gabrielle

Well, we finally got our “G” storm! Gabrielle formed out of the slop that was Tropical Depression 7 yesterday. And if there ever were a storm to typify this season, Gabrielle may be the one. It’s essentially a naked swirl this morning. Looking at it on satellite, you can literally see the wind shear impacting the storm.

Gabrielle’s low level circulation is evident, spinning right to left, while significant wind shear is evident in the clouds moving from bottom to top on the loop above. (Tropical Tidbits)

In addition to the shear, Gabrielle is also fighting dry air. Overall, this is about as pathetic as it gets for a tropical storm. It seems as though this is going to struggle mightily for the next 2 to 3 days. I wouldn’t be shocked to see it even be reclassified to a depression again at some point. Beyond that, the environment looks to get a little less hostile. This should support strengthening as the storm turns north and (likely) passes east of Bermuda. Some models still drag Gabrielle close to the island, but over 90 percent of the suite of solutions keeps it to the east.

The suite of a bunch of Google AI models (blue, green, purple) and the Euro ensemble (orange) show good agreement on Gabrielle passing east of Bermuda. (Google Weather Lab)

Given Gabrielle’s disorganization, it probably remains worth watching for Bermuda, because weird things can happen track-wise when you’re dealing with a system like this. Water temperatures in the subtropical Atlantic are quite warm, so assuming this gets to an environment that is less hostile, whenever it does get its act together (if it does), it could come together rather quickly. But at least for now, it’s not a real serious threat.

What comes next?

Well, the NHC took the 20 percent area off the board in the Atlantic and replaced it with a more generic 20 percent area for the next wave behind that one in the pipeline. This seems to be the season of “well, let’s watch the next wave.” Truth be told, when I look out beyond days 5 to 7 right now, I cannot point to much of anything other than vague “well, it’s September so we’re watching here and here maybe I guess.”

The background state of the Atlantic has been hostile all season, and it remains hostile, and I’m not sure I see where that’s changing. A lot of folks have mentioned the MJO, or Madden-Julian Oscillation, which is a periodic pattern of favorable conditions for thunderstorms (rising air) that works around the globe in the tropical regions. There is a fairly good correlation between supportive MJO activity and increased tropical risks. Much of this season has been spent in the unfavorable side of the MJO, with sinking air dominating the Atlantic. And it seems that every time the models suggest this may change…

So here we are in mid-September, without really much of anything showing up over the next 7 to 10 days. This gets us to about September 26-28, give or take. It’s important to recognize that October can still do bad, bad things. Very bad things. But at this specific moment in time we’re in good shape.

California rain

A slight risk of excessive rainfall and flash flooding is in place today for much of southern California’s mountains and deserts.

Flooding is possible in spots across SoCal today. (NOAA WPC)

Flash flood watches are posted from Yuma, Arizona through Yosemite National Park. While any flooding risk today is more or less isolated in nature, there could be some healthy rainfall rates with any storm. We could see some places with a tenth of an inch or less, and others that pick up 1 to 2 inches of rain in short order with flooding. A good day to be weather aware across SoCal, particularly north of LA up into the Central Valley as well as between Los Angeles and Las Vegas or east of San Diego to Yuma. The slight risk (2/4) focuses more on the Sierra on Friday.

Friday’s flooding risks are more focused on the Sierra. (NOAA WPC)

Another round of moisture increase could occur Sunday into early next week, bringing more rain chances to parts of California.