September 21, 2023 Outlook: What do we make of the upcoming action in the Atlantic?

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.

These maps show the GFS ensemble (L) and the Euro ensemble (R) and where their individual members place the tropical wave (then a defined system) next Tuesday afternoon. The background green shading indicates the IQR. Click to enlarge. (PolarWx/Tomer Burg)

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.

The upper pattern over the Atlantic shows the GFS ensemble (L) with a weaker high and a faster developing system that gets to about 50°W longitude by Monday. The Euro ensemble (R) is slower overall and bigger with the high, so the wave only gets to about 45°W longitude. Click to enlarge. (PolarWx/Tomer Burg)

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)

The Euro is slower with development of this wave and also farther north, while the GFS is much quicker to develop the system and is also farther south and west when it happens. These differences allow the system to get to the islands in some GFS ensemble cases but very few European cases. (Tropical Tidbits)

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.

An area of heavy storms offshore has a decent chance to organize into a relatively strong surface low and track north toward the Outer Banks or Sounds of NC, bringing impacts akin to a tropical 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.

Tidal gauges from Virginia to New Jersey are currently forecast to experience moderate tidal flooding with this system, with even a handful of gauges in the lower Chesapeake Bay near the mouth of the James River expected to infringe on major flooding. (NOAA)

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.

Rain totals averaging 2 to 5 inches will spread from Myrtle Beach to Long Island in the coastal plain, with some inland spread in North Carolina and Virginia.

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.

September 20, 2023 Outlook: Heavy rains possible this weekend in Virginia and the Carolinas, and watching a tropical wave

One-sentence summary

Two systems are worth watching late this week or weekend, a deep Atlantic Cabo Verde wave and a subtropical system off the coast of the Southeastern United States.

Happening now

There’s not much beyond the slowly fading Hurricane Nigel, which is making a turn to the northeast and will race out to sea harmlessly. It should become a tropical storm in a day or two, and then transition to a post-tropical cyclone as it encounters much colder waters over the Northern Atlantic Ocean. Nigel was the kind of storm we can all live with, a powerful beast that remained at sea and never threatened any landmasses. Would that they all were that way.

The medium-range: Two things to watch

Let’s start with the system closer to the United States, an area of low pressure off the coast of Florida in the Atlantic Ocean. This system may develop into a subtropical storm by around Friday, at which point it is likely to get pulled north toward the Carolinas and Virginia. This will bring a surge of moisture into the region, some high surf, and wind gusts perhaps in excess of 40 mph along coastal areas of North Carolina and Virginia.

NOAA rainfall forecast for now through early next week. (Pivotal Weather)

Probably the biggest threat this weekend to the Southeastern United States coast will come from heavy rainfall, most likely during a period from Friday through Saturday night, with some locations possibly seeing 4 to 6 inches. Tropical rainfall like this can come in bunches, so there will very likely be some localized flooding concerns regardless of whether this system develops or not. By Sunday, whatever this becomes should be pulling hard, away from the eastern coast of the United States.

African wave

As for the African wave, it only recently moved off the continent into the eastern Atlantic Ocean. Over the next few days it should find conditions well suited to further development, and it’s likely to become a tropical depression or possibly even a tropical storm by this weekend. After that? Well, that’s the big question.

The system should move more or less westward through the early part of next week. It seems fairly likely that the storm will get close to the Lesser Antilles, and perhaps Puerto Rico, about seven or eight days from now. At some point it will find a weakness in the high pressure ridge to its north, and lift away from the islands into the open Atlantic Ocean. But since this turn is not likely to occur for at least a week, and perhaps longer, our confidence in the details is understandably low.

This wave may, or may not, threaten the Caribbean Islands next week. (National Hurricane Center)

The bottom line is that this system is worth watching, particularly for places like Antigua and Barbuda, the Virgin Islands, and Puerto Rico. This storm could miss these islands, certainly, but we’re also looking at the possibility of a significant hurricane coming calling. We’ll track it on a daily basis for you right here.

Fantasyland (day 10 and beyond)

There’s not much to see here, especially as concerns tropical weather close to land. That’s just fine with me.

September 19, 2023 Outlook: Assessing the race for Ophelia between the Cabo Verde wave and Southeast subtropical shenanigans

One-sentence summary

Two systems may try to develop late this week or weekend, a deep Atlantic Cabo Verde wave and a subtropical system off the Florida or Georgia coast.

Near term Nigel

Let’s clear the deck first. Nigel? Still out there.

Nigel has had to deal with dry air, which has led it to struggle some, and it also has a mammoth eye. (

The stand out feature of Nigel is the size of its eye. It’s tough to specifically measure, but I am estimating this is about 40 to 60 miles across. Dry air has been a persistent issue for Nigel, and it seems to be impacting its intensity and holding it back from becoming more than a minimal hurricane. Nigel will continue to track northwest and then eventually north and northeast, out to sea, no threat to land.

The medium-range (days 6 to 10): Subtropical Southeast vs. Classic Cabo Verde

Two systems may enter. Both systems will eventually leave. The hope is that neither will produce any serious impacts to land. Let’s start close to home.

Southeast subtropical shenanigans

The general theme for this week will be: Upper low forms over Florida, drifts offshore to the east, undergoes a top-down process to form a surface low which may develop into a storm as it tracks north toward the Carolinas. It would probably be a subtropical storm, but the impacts would essentially be similar to a tropical storm, so I don’t want folks to get hung up on technicalities here. There will likely be a coastal storm this weekend that tracks north from Florida toward the Carolinas. Exactly where, how strong, etc. remains to be determined.

The impacts will probably include locally heavy rain, rough surf, possible beach erosion, and gusty winds on the South and North Carolina coasts.

Locally heavy rain in South Florida through the week that will spread north this weekend. Locally heavy rain is possible from the Carolinas up along the Jersey Shore toward southern New England this weekend. (Pivotal Weather)

The map above is a preliminary rainfall forecast through Tuesday morning. Florida gets their rain this week, locally heavy at times. As the system organizes that will spread north, certainly into the coastal Carolinas, but also perhaps up Delmarva, the Jersey Shore, Long Island, and southern New England. As of now, this looks like an early autumn nor’easter type impact. Although exactly what intensity the impacts of this system arrive with remains to be seen. We will have more on this tomorrow and Thursday.

Cabo Verde wave

The deep Atlantic is a little sloppy right now, but emerging from this mess will likely be the next wave off the coast of Africa. We continue to have model support for this to develop, however that support seems to have waned a bit since yesterday. The 70 percent chance of development assigned by the NHC is probably a good spot to be right now.

Anyway, this wave will come west over the next week or so and eventually end up near the Lesser Antilles or Puerto Rico. It may swing north of there, or it may enter the islands. It will be steered by high pressure over the central Atlantic.

High pressure near the Bahamas may help steer or orient the next Atlantic wave to either be tugged northward by the trough over the North Atlantic or sneak through as a lower-end storm into the Caribbean. Odds still favor a curve north. (Tropical Tidbits)

There is some chance that this high may build far enough west and south to perhaps block out the tropical wave or cause it to slow enough to be picked up by that trough in the North Atlantic. Odds probably favor that latter scenario in this situation. Still, I think in general this area merits watching because of the time of year, the warmth of the water, and the potential track. But it remains too early to say whether or not it’s a particularly serious concern for the islands. We’ll monitor it over the next few days.

Hopefully the most exciting aspect of these two waves will be who gets a name first, if either does. My bet is on the Southeast system today. The next two names are Ophelia (o-FEEL-ya) and Philippe (fee-LEEP).

Fantasyland (beyond day 10): Nothing brewing of note

We continue to keep an eye on the extended period to look for signs of trouble. As of now, it looks like things will be fairly quiet. Wind shear is expected to be well above average in the Gulf and northwestern Caribbean, which would be two key areas to watch in early October. So I’m cautiously optimistic that things will calm a bit, but as always we’ll keep watching.

September 18, 2023 Outlook: What is next in the tropical Atlantic pipeline?

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.

Hurricane Nigel is the only active storm currently, but the large wave emerging off Africa is likely to develop this week. (College of DuPage)

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.

Hurricane Nigel’s forecast from the Hurricane Center with sea-surface temperatures highlighted in the background. Nigel has a couple days over very warm water to become a major hurricane. (Tomer Burg)

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.

The forecast from the European ensemble for sea level pressure on Monday of next week shows a fair bit of uncertainty, much of which will be dependent on intensity of the next wave. Stronger outcomes turn north faster, while weaker ones will progress toward the islands. (Tomer Burg)

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.

The forecast view 20,000 feet up between Tuesday night and next Monday evening shows an upper low (blue) develop over Florida. A weak surface reflection may develop leading to a tropical or subtropical low and lower-end system drifting toward the Carolinas this weekend. (Tropical Tidbits)

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.