Matt Lanza

One-sentence summary

We discuss that the system off the East Coast this weekend will produce some notable coastal impacts, particularly from heavy rain and tidal flooding, and today we will assess the players that will shape the next Atlantic system near the Cabo Verde Islands.

Awaiting the next round of Atlantic action

Cabo Verde wave

Over the weekend, I noted how Hurricane Lee was emblematic of hurricane season, a marathon. You need to pace yourself to make it to the finish without losing your mind. Discussion about Lee lasted over three weeks, and it feels like we’ve already been sort of discussing this next Atlantic wave for about a week, and it’s just now awaiting the invest designation. This one has been a bit of a head scratcher, and we’re not a ton closer to resolution today on what will come of this. Let’s talk about what we do know.

Sometimes it makes sense to look forward before looking backwards. In other words, as a forecaster, sometimes I want to see what a model’s outcomes are before I go back and assess why it has that outcome. This is especially true when two of our more reliable models show two relatively different outcomes.

In the map above, you can see the forecast IQR, or interquartile range difference of sea level pressure in the Atlantic from the GFS ensemble (L) and the Euro ensemble (R). Explain this to you like you’re three years old? You got it. You have operational models, which are the ones that are deterministic; one run, one solution. Then you have the ensemble models which are the ones that run the model roughly 30 (GFS) to 50 (Euro) different times with tweaks each time to produce a range of outcomes. The maps above show you what the ensemble model outcomes say for sea level pressure of the 75th percentile minus the 25th percentile. In other words, how spread out are the outcomes within the majority of ensemble solutions? Or are they spread out at all? This will illustrate key differences and/or areas of higher confidence.

The European model is fairly tightly clustered east or northeast of the islands next Tuesday afternoon with the tropical wave, or whatever it is at that point. The GFS at left is slightly less tightly clustered, more spread out, and also faster, with a couple members even almost in the Caribbean next Tuesday. Interestingly, the IQR differences are not substantially higher on the GFS than the Euro, which may be a bit of a red flag for the GFS. But we’ll note that in our back pocket and operate under the idea that there are noteworthy differences.

So, we look at this and say, “Ok…the GFS is quicker and potentially near the islands, while the Euro is slower. Why the difference?”

So we’ll next look up, about 20,000 feet at the 500 millibar level to get a sense of what is steering the wave.

If we look at the forecast at 500 mb next Monday morning, we see the Euro and the GFS differ in terms of location and size of the high pressure system in the central Atlantic. The Euro is stronger and maybe actually holding the system up a bit. But the high pressure center moves out of the way, and an exit door into the open Atlantic awaits. Thus, the risk of the system making it into the Caribbean on the Euro is low.

But if you look at the GFS, the high is weaker, and a hair farther north, which probably allows the system to move a little faster, and it gets to the islands in some ensemble member cases before it can curve out to sea.

We can take this a step further to see which model develops the system faster. The GFS tends to be quicker to the punch than the Euro (forecast for Sunday morning shown here)

So what does all this tell us? The GFS is quicker to organize the wave, moves it faster west, and by the time the escape route north opens, the system may be bearing down on the islands. The Euro is slower, organizes the wave slower, and when the escape route opens, it’s still probably several hundred miles east of the islands and likely to hook northwest or north. Those are fundamental differences hinging on how the high develops and how the wave develops and interacts with other things surrounding it, questions we cannot adequately answer yet. But at least we have a cheat sheet of sorts now that we can apply to this wave. And we should know in a couple days if the islands are seriously at risk or if the northward solution is more likely. Stay tuned.

East Coast subtropical sloppiness

We continue to see a good chance that a surface low is going to develop well off the coast of Florida or Georgia tomorrow or Saturday. Look for that to wobble generally north up the coast and either into the Outer Banks or just ride up the East Coast toward Delmarva or the Jersey Shore as a subtropical storm or strong nor’easter.

A subtropical designation just has to do with how the storm forms, and it has no bearing on the impacts. What will those impacts be? Well from the upper coast of South Carolina into most of North Carolina, coastal Virginia, Delmarva, and the Jersey Shore, we can expect rough surf, gusty northeast winds, moderate to locally major tidal flooding, beach erosion, and rip tides, in addition to heavy rain. This may be a step above nuisance status in some places now, akin to a rather strong nor’easter.

We are looking for a wide swath of 2 to 5 inches of rain on the Coastal Plain from Myrtle Beach through Long Island. This may cause flooding, particularly in lower-lying and urban areas. Coastal communities may see high tides exacerbated because of heavy rain, so this could slow the drainage process for a tide cycle or two this weekend.

We will be keeping you posted on the East Coast storm, as well as the progress in the forecast of the Atlantic system through the weekend.

A quick thank you to the new followers we’ve gained over the last couple weeks, especially in New England and Atlantic Canada! We hope you’ll stick around going forward as we continue to cover the Atlantic and eventually branch out into other significant and extreme weather later this autumn and winter. Spread the word!

One-sentence summary

Nigel is expected to swirl out to sea through the week, while we watch the next wave off Africa as perhaps making it a little farther west, as well as a potential lower-end system off the Southeast this weekend.

Near-term: Margot & Nigel

We’ll use this week to sort of recharge after 3 weeks of Lee, which was preceded by Idalia. This patterns can really take a lot out of you, and it’s important to pace yourself during hurricane season as a resident, forecaster, or decision-maker. At present, we’ve got one system out there and a second or even third that we’ll see toward the weekend.

Nigel is not a big deal in terms of impacts. It will likely become a major hurricane as it lifts north and eventually northeast. While Nigel will likely turn out to sea before affecting any land, it will probably (again) kick up surf for Bermuda. Nigel seems to fit the theme of the 2023 Atlantic hurricane season.

Meanwhile, Margot got the downgrade yesterday, losing tropical characteristics. It will meander in the eastern Atlantic for a few more days.

The medium range (days 6 to 10): Ophelia (?) in the Atlantic and watching the Southeast

The National Hurricane Center has tagged the next disturbance to move off Africa with about a 70 percent chance of development over the next 7 days. There’s a slight chance this could develop at the end of the near-term, but for our purposes, we’ll focus on this for the medium-range.

Anyway, this wave seems to have a decent shot at perhaps becoming a depression by about Thursday or Friday. This one has a little more uncertainty behind it in terms of track. If this thing can come out of the gate roaring and quickly develop, it will almost certainly follow Nigel or Lee or something in between and curve north quickly, avoiding the Caribbean islands again. If this disturbance struggles late this week and weekend and fails to organize, it will likely come west, with at least some chance of getting to the islands. It’s a little early to say much more about it than that, but it’s at least worth checking in on again Wednesday or Thursday to see what has happened. Really, the only thing we’ll be keeping an eye on the next couple days will be odds it develops quickly, which right now *seem* high, but you never can be too sure.

The other system to watch may or may not be a thing, but the NHC is giving it a slight chance to happen by the weekend. An upper level dip in the jet stream over the Southeast and Florida may allow a surface low to develop off the Florida coast by Friday or Saturday. If that happens, it will have a slight chance to develop into a tropical or (more likely) subtropical entity.

In all likelihood, it would probably track north, slowly, toward the Carolinas, and I would imagine that the intensity ceiling on this one would be fairly low. In other words, we’ll probably see slow, lower-end development, not rapid, high-end development. So, something to watch, but probably not something to fret much about. As of now, the vast majority of the rain associated with the upper low or potential system would be focused offshore. But any tropical system could kick the surf up again in this area, and we could see issues with beach erosion and such. We’ll keep you posted.

Fantasyland (beyond day 10): No specific concerns

I don’t necessarily have an opinion today on the long range portion of the forecast. I don’t see anything scary on any modeling, but I’m not actually convinced it will be quiet. So this is a true “punt” on the forecast right now. But the key point is nothing specific stands out right now. We’ll keep you posted.

One-sentence summary

Post-tropical cyclone Lee is on its way across the Gulf of St. Lawrence and should be completely out of the picture by tomorrow morning, tracking well south of Greenland.

Post-tropical Lee: 45 mph, moving NE 22 mph

We first started talking about Lee as it was about to become Invest 95L back in the closing days of August while Idalia was readying to impact Florida. When we say hurricane season is a marathon, not a sprint, this is what we mean. Now, mercifully after nearly 3 weeks of tracking, Lee is implementing its exit strategy across the Gulf of St. Lawrence and eventually out to sea.

Lee’s center is off the coast of PEI and moving toward the Great Northern Peninsula in Newfoundland. Lingering tropical storm conditions will continue over PEI, portions of Nova Scotia, and Iles-de-la-Madeleine. Gusty winds are expected in Newfoundland, but impacts should be relatively minor. Rough surf will continue across Atlantic Canada, but any risk of damaging tidal flooding has diminished.

Rain totals were a bit spread out, but I found over 5 inches near Eastport, ME, almost 5 inches (125mm) near Fredericton in New Brunswick, and there were reports of around 100mm in Gaspe in Quebec and Grand Manan just east of Maine.

Nova Scotia power reports about 75,000 customers without power as of 11 AM (ADT), there are about 12,000 without power in New Brunswick, and about 40,000 in Maine.

That about closes the book on Lee.

Elsewhere

We’ll go into more detail on this tomorrow or Tuesday, but the rest of the Atlantic is busy but of no concern. For now. Nigel and Margot will not impact land, though Margot could brush the Azores as a remnant depression. The next wave, which the NHC gives a 40 percent chance of development over the next week is worth watching, particularly in the Caribbean, as there are questions as to exactly what the steering pattern in the Atlantic is going to look like when it gets there.

I would say the odds still favor a track north of the islands, but confidence in this is far less than it was for Lee, Margot, and Nigel.

Otherwise, there is at least reason to watch near Florida this week, as an upper low may develop in the neighborhood. While that seems unlikely to lead to a surface low developing, you never can be certain. Regardless, it means increasing rain chances for Florida and perhaps the Bahamas and Southeast. We’ll see how things evolve. More tomorrow.