September 6, 2023 Outlook: Lee plodding west-northwest and strengthening; where will it ultimately go?

One-sentence summary

While Tropical Storm Lee’s ultimate future is unknown, it is likely to become a hurricane today, and it is still forecast to miss to the north of the islands with some modest fringe impacts there.

Tropical Storm Lee: 65 mph, moving WNW 14 mph

Lee is forecast to become a hurricane today and a major hurricane tomorrow and is still expected to go north of the Caribbean islands. (NOAA/Tomer Burg)

What’s changed since yesterday?

Invest 95L became Tropical Depression 13 briefly, and then it became Tropical Storm Lee yesterday afternoon. It is organizing and tracking west-northwest. Confidence that it will miss a direct impact on the islands is increasing. Confidence on anything beyond there is low.

Lee’s intensity

Lee is in a tremendously ideal environment for intensification. It has deep warm water, low shear, and plenty of moist air in the neighborhood for the next 5 or 6 days. Models have suggested since last week that this would go to the moon intensity-wise, and there’s no reason to doubt that today. The NHC forecast for Lee was one of its most aggressive on record, taking it to a category 4 storm by Sunday or Monday, something they will not commit to without confidence.

Lee is developing nice outflow and maintains a solid core. It will likely take on a “classic” hurricane look in a couple days. (Weathernerds.org)

Once Lee manages category 4 or 5 intensity by Friday or Saturday, it will likely fluctuate in intensity up and down for a few days, probably remaining a major, if not Cat 4-5 storm much of the time. Heading into next week, the question will become where Lee tracks relative to the cold wake in the Atlantic from upwelled water left behind by Hurricanes Franklin and Idalia.

There is much cooler water southwest of Bermuda that could impact Lee’s intensity next week as it comes northward. (Tropical Tidbits)

So, for now, expect a pretty impressive hurricane into early next week, followed up by some potential significant fluctuations in intensity as it comes northwest.

So where is Lee headed?

We have about 5 hurdles with respect to Lee’s track over the next 10 days or so. First, Puerto Rico and the Leeward Islands. Second, the Turks and Caicos and southeast Bahamas. Third, Bermuda. Fourth, the US coast, and lastly the Canadian Maritimes.

First, with respect to Puerto Rico and the islands, Lee is expected to pass to the north, comfortably enough to avoid significant impacts but definitely close enough to keep watch and expect fringe impacts (a few outer bands with gusty winds, rough surf, rip currents, etc.). So if you’re in Puerto Rico or the Virgin Islands, stay tuned and keep watch, but you are almost at the point of being able to exhale.

Beyond that, it remains to be seen what happens. Lee will be steered around the periphery of high pressure over the Atlantic. This should ensure it gets to a point northeast of the Bahamas early next week. From there, the players on the field become more difficult to assess. How strong is the high? Does it collapse, weakening steering currents? If it doesn’t collapse, where is it centered? Will the trough over the Great Lakes be strong enough to try to “capture” Lee and draw it more toward the East Coast? If Lee splits the gap between Bermuda and the Carolinas, will New England or the Maritimes be in the way on its way out? Will Lee be strong enough to just barge north toward Bermuda anyway? How much of a role will the cooler water out there play in Lee’s intensity? The map below shows the situation on Sunday evening.

Sunday evening’s upper air map shows high pressure near Bermuda which should keep Lee going northwest or west-northwest. After Monday, however, the steering currents may slow Lee down, making it susceptible to a lot of possible outcomes. (Tropical Tidbits)

There will be some people out there speaking with conviction about the future of Lee, and if so, you can tune them right out. Every question I just rhetorically asked has no answer yet. None. I personally think Lee will split the gap between Bermuda and the Carolinas and then hook out to sea, but I see a path where the trough digging in from the Lakes could try to draw it back west, especially if it’s weakened some by the cooler water west of Bermuda. I see how it could hit Bermuda directly or pass very close. I see a path where it misses Bermuda and the US but runs into Atlantic Canada. What I don’t have is confidence in any of those outcomes right now. There are too many “known unknowns” for confidence. I realize this answer won’t generate a lot of excitement, but this is exactly why we’re here…to provide sober, steady analysis of significant storms. Welcome to The Eyewall!

Anyway, let’s keep tabs on this over the next few days, and we’ll monitor the progress of the features that will steer Lee in the future. One thing I can say with confidence? Expect more rough surf and rip currents on the East Coast next week.

Beyond Lee

We recycled into Invest 96L yesterday, which is a very robust tropical wave just off the coast of Africa. That has a decent chance to become either Tropical Depression 14 or Tropical Storm Margot in the coming days. It is unlikely to threaten land other than some initial heavy rainfall in the Cabo Verde Islands.

Invest 96L may nudge across the Cabo Verde Islands before it develops, slowly, over the weekend into next week out at sea. (Tomer Burg)

After we get past 96L, there is a minimal chance of additional development in the Atlantic next week. The Gulf looks closed off, as does the western Caribbean, loaded with shear. The overall background state of the basin should be hostile to tropical development into next week. We may flip back to a more lively pattern again in the final 10 days of the month. We’ll see!

Taking stock of the 2023 Atlantic hurricane season so far: Active with headwinds; more to come?

One-sentence summary

With the historical peak week of hurricane season upon us, we take a look at what has happened so far, how seasonal forecasts have performed, and what we can glean for the rest of hurricane season based on the active start and El Niño.

How are those seasonal forecasts holding up?

Back in June when we launched The Eyewall, one of the things we did was dive into the components of the seasonal forecast. We explained that the 2023 hurricane season would be trickier than normal, as the developing El Niño, which typically reduces storm activity would be battling an outrageously warm Atlantic Ocean, a feature that would be good for busy storm activity. So far, that battle seems to be exactly what’s playing out. The “consensus” forecast was 16 named storms, 7 hurricanes, and 3 majors. As of Monday, we sat at 12 named storms, 3 hurricanes, and 2 majors.

Our accumulated cyclone energy for the season, or ACE, sits around 125 percent of normal for the first week of September.

As of yesterday, the Atlantic was running about 125 percent of normal activity, from an ACE standpoint. (Colorado State University)

If the season ended right now, we would be sitting in the upper tier of “below normal” seasons. In other words, we already have one heck of a base and seem to be on our way to (at worst) an average season. The seasonal forecasts did a good job telegraphing this, and frankly some of the more active seasonal forecasts that I believed were more out of an abundance of caution are the ones most likely to verify.

And this isn’t because of ticky-tack storms that last a day or two. Idalia, Don, and Franklin, the three hurricanes account for nearly 75 percent of the seasonal ACE to date. So three legitimate storms make up the majority of the total. Back in June we said that we believed the Caribbean would struggle (it mostly has), the eastern Atlantic would be busy (it’s been more the central Atlantic, so that point is a little fuzzier), and that the most concerning items this season would be systems forming close to home (Idalia counts for that). So thus far, this is going mostly as expected, if not a little bit busier. Kudos to the seasonal forecasters for not just going all-in on El Niño.

Where are we going?

Well, this week we are likely to see another big jump in seasonal ACE when Lee forms.

The likely track of future Lee should go north of the islands but may impact Bermuda. It’s going to be a very strong storm. (Tomer Burg)

From our morning post, you can read how we expect that to become a major hurricane, likely at least a category 4 storm. This will be a big ACE adder, and I suspect we’ll see things shoot up at least into the 70s once Lee is done, pushing us into the “average” tier of seasons if it ended right there. Behind Lee, we may get another storm in the eastern Atlantic, so there’s an opportunity for a few more ACE units.

But here’s something. If you look at the European ensemble model forecast for wind shear in days 11 to 15, which pushes us out to near September 20th now, you can see that the Gulf and western Atlantic are ripping with shear.

Wind shear is forecast to remain well above normal in the Gulf and western Atlantic for mid-month. (Tropical Tidbits)

If that happens as forecast, anything in the Gulf will struggle, as would anything coming out of the Caribbean. However, the lower wind shear in the eastern Atlantic and central Atlantic suggests these would be the areas where storms could continue to form, continuing the legacy of the 2023 season to date. We may see less hostile conditions return to the Gulf and western Atlantic in the final days of September, but that’s obviously a long way off.

What does El Niño tell us?

Quite frankly, if we assume that El Niño is up and humming now and the influence is strengthening, then we should expect to see a lot of what we’ve already seen for the remainder of hurricane season. Here is a map of all hurricanes in Septembers and Octobers since 1950 when the Oceanic Niño Index (ONI) was 1.0 or greater for June-July-August (this year’s value is 1.1).

Hurricane seasons most similar to this one in terms of El Niño produced a lot of central Atlantic storms in September and October and not a lot of serious land impacts. (NOAA)

With a couple notable exceptions, this map shows a lot of fish storms and middling systems in the western Atlantic. The two most notable exceptions were Joaquin in 2015 which killed 34 people (33 of whom were aboard the El Faro). And also Betsy in 1965, which killed 81 and inundated New Orleans. Emily in 1987 hit Hispaniola and Bermuda. And I think that sums up the season so far: A lot of middling storms and mostly fish storms with one potent hit in Idalia.

All in all, given what we see on the maps right now and given how this season has gone, there are two primary areas that probably should watch for land impacts: Bermuda and the Greater Antilles. If we can relax shear enough late in the season and get a disturbance in the Caribbean that comes straight north, you never know what you can get out of that, and those often threaten Cuba, Jamaica, Hispaniola or the Bahamas. Bermuda remains in the target line I think for at least one or two more storms. Lastly, the eastern Gulf or off the Southeast coast may be secondary areas to watch, given the warm waters and potential for just the right things coming together at the wrong time, sort of like what we saw with Idalia and to a far less impactful extent, Harold in Texas earlier this season.

Will it be enough to drive ACE above normal for the season in the end? I’m not certain, but it will be close.

September 5, 2023 Outlook: Invest 95L should go off to the races and hopefully out to sea

One-sentence summary

Invest 95L is very close to becoming our next tropical depression or storm, and it is expected to rapidly intensify this week passing just north of the Caribbean islands and worth keeping an eye on in Bermuda.

Invest 95L

Invest 95L is close to becoming a depression or tropical storm this morning. It’s got plenty of thunderstorm activity associated with it, and it’s beginning to show a little “twist” now on satellite loops. I would expect Tropical Storm Lee to form before day’s end.

Invest 95L (center) should become Tropical Storm Lee later today. (Weathernerds.org)

We expect this system to go off to the races over the next few days. Thankfully, that should allow it to gain the latitude needed to bypass the islands to the north. Because I have to tell you, the intensity forecast for 95L is one of the most impressive I have ever seen for an Atlantic tropical system.

A majority of tropical modeling that’s tracked calls for 95L to eventually become a major hurricane, if not a category 4+ storm. (Tropical Tidbits)

For those that are astute watchers of hurricane models, you’ll know the HWRF model tends to bias to the high side with intensity, and we’ve seen some wild forecasts over the years from that one. But seeing essentially all the tropical models close to or all aboard the Cat 4 train with this one from pre-inception has been something to witness. Expect to see quite a show in the Atlantic this week.

Invest 95L is expected to miss the islands to the north, but from there, where it goes relative to Bermuda is a difficult question to answer. (Tomer Burg)

Assuming we have the next 72 to 96 hours mostly baked in, the biggest concern now is what will happen once this thing turns. Will it split the gap between the Carolinas and Bermuda and hook back out to sea? Will it turn sooner than that and actually go east of Bermuda? Or will Bermuda be in the way? The quick intensity gain expected this week is great for the Caribbean, but it may be precarious for Bermuda. As the system grows and rounds the periphery of the ridge, it will also probably erode the western flank enough to turn from northwest to north fairly quickly. You can see hints of that on the map above. From there it becomes a game of exactly where that happens and how much space it has to erode the northwest periphery of the ridge to turn northeast and ideally away from Bermuda. It will be close. Hurricane Sam in 2021 may be a decent analog to this one.

Either way, at this point, if you’re in Puerto Rico or the Virgin Islands, keep tabs on this to make sure it does what is expected. If you’re in Bermuda, watch closely later this week to see how it trends. If you’re on the U.S. Eastern Seaboard, another round of rough surf and rip currents may be on the menu next week.

Elsewhere

Things look mostly uneventful in terms of land impacts over the next 7 to 10 days. We have another wave emerging off Africa today that has a chance to develop over the next 5 or 6 days way out in the eastern Atlantic.

A lot of remnants in the Atlantic, but presently only 95L is of immediate concern. A system emerging off Africa will likely develop in the coming days and turn out to sea. (College of DuPage)

The remnants of Hurricane Franklin are back on the map today, as it circles back south to a spot in between the Azores and Portugal. Significant development seems unlikely, but whatever is left of this could end up near Iberia later in the week or next week.

Otherwise, that’s about all. The Gulf and Caribbean look quiet for the foreseeable future.

Later this morning, we’ll have a post looking at how we stand as we arrive at the peak week of hurricane season. How have seasonal forecasts done so far? And what do we expect from the rest of the season? Look for that around 11 AM ET/10 AM CT.

September 4, 2023 Outlook: Invest 95L should soon develop and hopefully thread the needle north of the Caribbean islands

One-sentence summary

Invest 95L is expected to become a depression or tropical storm soon as it comes west across the Atlantic, likely passing just north of the Caribbean islands, though it merits some continued watching.

Invest 95L

On satellite, Invest 95L is beginning to slowly get itself together. It has thunderstorms that have persisted, indicated by the brighter colors on the satellite loop shown here. It’s got a little swirl to it, but probably not quite enough to indicate a surface low is present.

Invest 95L is slowly beginning to get its act together. (Tropical Tidbits)

But it’s getting there, and that’s the takeaway today. The National Hurricane Center has boosted odds of development to 90 percent over the next several days. And this seems to be in line with almost all model guidance that shows this developing.

Invest 95L’s track

The track and intensity forecasts are somewhat intertwined. As is often the case, a stronger storm will be more apt to get steered poleward, or toward a recurve north. A weaker storm won’t get as much latitude. So the speed at which 95L organizes is somewhat important. Given that it is already starting to establish some structure, my thoughts today lean toward the stronger outcome and a faster recurve. That said, this remains a very close call in the islands.

Models have actually been in very good agreement through about day 4, which gets 95L some decent latitude. By day 5 (shown on the Euro ensemble mean below), 95L should already be near the same latitude as Puerto Rico. As long as that occurs, it should miss the islands to the north.

Invest 95L will be steered around a somewhat convoluted high pressure system in the central Atlantic. As long as 95L strengthens steadily this week and gradually builds latitude, it should curve out to sea north of the islands this coming weekend. (Tropical Tidbits)

So we believe that 95L will stay north of the islands, but it will be close. Of the many model ensemble members from the GFS, Euro, and Canadian models, about 90 to 95 percent or so stay north of the islands.

The majority of the model ensembles we look at for forecast keep 95L north of the islands this coming weekend. (Tomer Burg)

So the odds are generally good for minimal land impacts as 95L comes west. This is good, as the majority of model guidance shows this becoming a major hurricane in about 4 days. But still, you don’t rest entirely with 5 to 10 percent bringing it much closer. We’ll keep watching.

Beyond the islands

Once 95L (or likely Lee by that time) gets north of the islands, where it goes is a bit of an open question. Will it truly recurve north and threaten Bermuda or turn out to sea? Will it turn north but then turn back more west-northwest and threaten the Bahamas or the U.S. coast? How will the cooler water recently upwelled from Franklin and Idalia impact it if it comes north? It’s too early to say anything with confidence here, so we’ll leave it at that for now. Stuff for us to watch this week.

Elsewhere

We may see another system attempt to develop and basically follow in Katia’s footsteps way out at sea in the open eastern Atlantic. But aside from that and 95L, truthfully things look quiet, a potentially decent outcome for mid-September in the Atlantic.