Eric Berger

In brief: Today’s update looks at the time remaining in the Atlantic season, which is dwindling. We also dig into a tropical system approaching the Caribbean Sea that will need to be watched closely in the coming days.

The finish line is in sight

Officially, the Atlantic hurricane season runs from June 1 to November 30 every year. Storms can form outside of these arbitrary dates, of course, and they often do. But the vast majority of tropical activity, and especially hurricanes, occur during these six months. Looking at the calendar this morning, we have a little more than 43 days left until November 1. So the finish line is in sight, and overall activity is definitely trending downward as the Atlantic basin cools. But we’re not there yet, so let’s jump in.

Southern blob

Let’s start with the southernmost blob on the National Hurricane Center’s forecast map, because that is of far more interest to pretty much all concerned. The forecasters at the hurricane center give this tropical wave a 30 percent chance of becoming a depression or tropical storm over the course of the next week as it moves westward, into the Caribbean Sea.

What we can say for sure is that the tropical system will bring a round of stormy activity, including heavy rainfall, to the Windward Islands this weekend. However we don’t expect tropical storm-force sustained winds or a significant storm surge. The question then becomes, what next? We of course don’t have any absolute answers for you. However, there is general agreement among most of our models that a low pressure system will be in the Central Caribbean Sea by around next Wednesday.

After this, well, we can’t really say much intelligent. There is potentially a corridor that could open to allow the tropical system to lift north during the middle of next week, toward Hispaniola or Puerto Rico. Alternatively, the system may just slowly meander westward in the Caribbean Sea (perhaps reaching Central America, and perhaps not) for a few days before finally moving north or northwest. I think the biggest point of concern I have is that, although we have reached mid-October, the Caribbean Sea remains plenty warm to support the development of a hurricane if other conditions are favorable. So we are going to keep a close eye on this one in the coming days.

Northern blob

This is non-tropical low pressure system that has a very slight chance of becoming an extra-tropical system during the next couple of days before reaching much colder water in the Northern Atlantic. Really, I think some forecaster at the hurricane center must have fancied the color yellow, and wanted to add a little more to the map, because this system is likely to be inconsequential.

In brief: There is a lot to talk about in the Atlantic tropics this morning, but the headline remains an as-yet unformed storm that is likely to become a tropical depression near the Bahamas soon. After that there is an increasing possibility that the tropical system will approach the southeastern United States by next Monday or Tuesday.

Invest 94L

We start with the storm most people will care about the most: an area of low pressure now moving away from Hispaniola toward the Bahamas. The system does not yet have a closed circulation, but it will encounter favorable conditions as it pulls away from the Caribbean landmasses toward the open waters of the southwestern Atlantic Ocean.

We are fairly confident about the evolution of the storm through the weekend, as it should become a depression and then probably Tropical Storm Imelda. By Monday, when we look at a broad range of traditional and AI model solutions, we see that the system should have moved to the north of the Bahamas, and be located somewhere off the southeastern coast of the United States. The map below shows the model outputs for 8 am ET on Monday morning.

After this time frame we see a pretty broad divergence in the models. A majority of the solutions, but not an overwhelming majority, bring the system toward the Carolinas by around Tuesday. However a non-trivial number of models peel the system back to the east, into the open Atlantic, due in part to some complex interactions with Hurricane Humberto. Anyone having confidence in what, precisely, will happen at this point is probably not being honest with themselves (or you).

In terms of intensity the models are not super bullish on this blowing up into a major hurricane. In fact, the majority of solutions keep the system at a tropical storm or Category 1 hurricane level. Again there is a lot of uncertainty here, so something to continue watching.

What I am reasonably confident in saying is that there is real potential here for a rainmaker in the Carolinas, and particularly North Carolina. Readers there will certainly and understandably be concerned that this could become another Hurricane Helene-like event. For now, we think that is unlikely, as the strongest rains appear to be east of areas most impacted by Helene, and the overall signal for prolonged, heavy rainfall is lower this time. For now NOAA is predicting 6 to 10 inches of rainfall for areas hardest hit, which is no picnic, but also far from reaching Helene-levels.

We are also monitoring storm surge and wind threats, which of course will be highly dependent on the track and intensity of the storm.

Hurricane Humberto

Humberto has become a hurricane, with 75 mph winds. Fortunately this storm is further out to sea than Invest 94L, because it is highly likely to blow up into a major hurricane over the next several days. The storm’s biggest threat will likely be to the small island of Bermuda.

At present Humberto has about a 40 percent chance of bringing tropical storm-force winds to Bermuda early next week, likely on Tuesday. There will also be the potential for storm surge, but my hope is that the hurricane is weakening and remains far enough west of Bermuda to spare the island more than a glancing blow. We will keep a close eye on the track over the weekend.

Gabrielle

This storm is no longer tropical, but it still managed to bring significant winds and waves to the Azores. It could also bring tropical storm-force wind gusts into Spain by Sunday, along with some much needed rains for the Iberian Peninsula.

In brief: Today’s post reviews the seasonal activity we have seen so far in the Atlantic Ocean. Then we turn our attention to the next wave on deck, and potential mischief in the Caribbean Sea.

Wednesday marked not just hump day for this week, but also the statistical midpoint of the Atlantic hurricane season. It’s been an odd season so far. There has been one very powerful hurricane, Erin, which formed in August, and five modest tropical storms. Additionally, although Erin was by far the most intense and long-lasting system, arguably the season’s most impactful storm was Barry, which made landfall in Mexico as a weakening tropical depression. It was moisture from these remnants that contributed to devastating flooding in Central Texas over the Fourth of July holiday, causing more than 135 deaths and causing widespread damage.

Going by raw statistics, the tally of six named storms to date is probably a little behind where we would expect to be during a season in which, on average, 15 named storms were predicted to form. In terms of Accumulated Cyclone Energy, which factors in the the duration and intensity of tropical systems, this season is running about 25 percent below normal. Without Erin, it is worth noting this season would be pushing historic lows in terms of overall activity.

So, overall, we are seeing less activity than is normal. Will that last?

Next wave up

Yesterday the National Hurricane Center started to flag a tropical wave that has not yet even emerged off the coast of Africa, into the Atlantic Ocean. (As a quick reminder, because it can be a little confusing, when forecasters refer to ‘tropical waves’ they don’t mean large waves in the ocean, but rather perturbations in the atmosphere). Anyway, when it reaches the Atlantic, this wave should find favorable conditions for further development.

Most of the various models we look at, including traditional physics-based models as well as AI models, have become fairly bullish on development of this system about a week from now. There is surprisingly good agreement among several of these models, and their ensembles, about where the disturbance will be by the middle of next week.

After that point there’s not a whole lot of agreement, and at six or seven days we are entering the realm of speculation. Some solutions never really develop the system beyond a tropical storm while others bring a stronger storm close to Puerto Rico or north of the islands. Other models predict dissipation, and are a lot more excited about another wave that is several days behind this one. All of this to say: This is something we are going to have to pay attention to for awhile, since the second half of September can see storms get pretty strong, pretty quickly. It could be something. It could be nothing. We’ll see!

Home brews?

The other thing we’re watching for is development of a tropical system closer to home, possibly in the southern Gulf of Mexico or more likely related to the Central American Gyre, an area of low pressure over the eastern Pacific Ocean and western Caribbean Sea. There is nothing imminent here, but it is the time of year when this thing happens, and some of the models (such as the ECMWF, shown below) are splashing low-end chances for formation. Given the overall pattern in the Atlantic right now, the best odds for a storm getting into the Gulf of Mexico in September will probably come from this kind of home-brewed system. But that does not mean the overall odds are particularly high.

Given that we are presently right at the peak of the Atlantic season, this is pretty good place to be in with just a few nebulous threats. We’ll keep a close eye on things in the days ahead to see what, if anything, comes from all of this.

In brief: Hurricane Erin is getting stronger again, and it may reach major hurricane status as it passes by the Carolinas and brings impactful storm surge to the Outer Banks. We also take a look at what is coming next in the Atlantic, and we are cautiously optimistic about things heading into September.

Hurricane Erin status

As of 11 am ET this morning, Hurricane Erin has continued to regain some of its former strength. The system now has sustained winds of 110 mph and a central pressure of 941 mb. Additionally, its eye has a better appearance on satellite which is another indication of better organization. The storm has about a day, or a day and a half to intensify further before wind shear should start to work on it. Confidence remains high in the track forecast, with Erin set to split the difference between the US mainland and Bermuda before moving out to sea later this week.

Storm surge along the Carolinas will build over the next day, with inundations of 2 to 4 feet above normally dry ground expected. This surge should be most impactful for the low-lying Outer Banks area, leading to numerous roads becoming impassable. Additional concerns include significant beach erosion, and sand being washed onto roads. Tropical Storm Warnings are in effect for coastal areas of North Carolina and Virginia.

A Tropical Storm Watch is also in effect for the island of Bermuda, where there could be high winds and dangerous surf and rip currents.

All that being said, we’ve largely been fortunate with Erin, being that it was such a powerful storm that got close to many landmasses but never directly threatened a landfall. We’ll be glad to put this system in the books over the next couple of days.

What’s next?

With the forecast for Hurricane Erin well in hand, it’s time to look ahead to what is coming next in the Atlantic season. Now that we’ve had the season’s first hurricane (and major, and Category 5 storm) it seems clear that the Atlantic tropics are open for business. We are now firmly in the most frenetic time of the year for Atlantic activity, the period from mid-August through mid-October.

But for the rest of August, at least, the tropics look pretty tame. I don’t want to manifest anything and I am certainly not tempting Mother Nature, but I like the setup for the rest of the month. Moreover, when we peek ahead at conditions for early September, there just is not too much evidence that things are going to start sizzling any time soon. For example, here’s the latest sub-seasonal forecast from the ECMWF model for the first week of September. As you can see, it is predicting just 40 percent of normal activity in the Atlantic basin. Of course such models are far from perfect, but you would rather see such forecasts than the alternative.

With that said, let’s take a look at what we’ve got going out there.

Central Atlantic disturbance

This tropical wave continues to propagate westward, and is edging closer to the Caribbean Sea. As of this morning, the National Hurricane Center gives the system a 60 percent chance of becoming a tropical storm or depression over the next week.

There are a variety of solutions for this system, which is natural since there is no clearly (or even poorly) defined center of circulation this morning. This makes it more difficult for models to latch onto a center and project it forward. Generally, however, most of our model solutions bring the storm northwestward, likely missing a majority, if not all of the Caribbean Islands. The image below shows the cluster of outcomes from the European model ensemble, and as you can see this is probably a fish storm.

The other thing to note is that if the storm does come closer to the Caribbean islands, including Puerto Rico, it likely is to be weaker (perhaps not even a depression) than if it recurves northward more quickly. The bottom line is that the upper-end intensity of this storm does not look all that high, and if it does get strong it’s probably going to miss land entirely. So we’ll watch it, but not with too much concern.

Invest 99L

The system behind that one actually got tagged as an “area of investigation,” but I’m not overly enthused about its prospects either. We can probably expect this wave to meander westward across the Atlantic and it may eventually move into the Caribbean Sea. As Matt noted yesterday these waves can be tricky, because they spend days doing nothing and then find a favorable patch of atmosphere and organize quickly. But for now there is virtually nothing, zilch, and nada in our models to indicate this will happen with 99L. So we’ll keep an eye on it, partly because beyond this there’s not much else expected to happen over the next 10 days.

Which is a great place to be in late August.