Eric Berger

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.

In brief: Today’s post discusses our increasing confidence in the track for Tropical Storm Erin, and takes a look at some of the near- and long-term risks from this system, which should become a hurricane by this weekend. We also discuss a new Blobby McBlobface in the Gulf.

Status of Erin

As of Wednesday morning the Atlantic season’s fifth named storm retains a fairly ragged appearance on satellite, with the National Hurricane Center (a bit generously, maybe?) holding Erin’s intensity at 45 mph. The system continues to encounter somewhat dry air, and sea surface temperatures that aren’t exactly sizzling. So Erin is just kind of slogging westward across the Atlantic. But it is making progress, having moved about halfway between Africa and the Leeward Islands; and Erin continues moving with purpose, at about 20 mph. On this path the storm should find more favorable conditions in the coming days.

Those conditions include warmer water and, crucially, rising air that should support further intensification. Accordingly, the National Hurricane Center expects Erin to become a hurricane by Friday, and potentially a major hurricane by this weekend. This is well supported by a suite of models we look at, and seems like a reasonable best guess. Bottom line, Erin is still very likely to become this season’s strongest storm to date, by far.

OK, so where is Erin going?

After several days of uncertainty, our confidence in Erin’s track is increasing. Although it is moving west now, it should slowly turn west-northwest by Friday or Saturday, and then northwest on Sunday as it finds a weakness in the high pressure system to its north. By early next week the storm’s center should lie somewhere to the north of Puerto Rico or Hispaniola, and be turning further north.

If we look at the overnight guidance there is a lot of support for this track, and it helps build our increasing confidence. Along this track the center of the storm should approach Bermuda by Wednesday (give or take a day) next week. We’re not saying the track of Erin is a done deal here, as there remains a broad range of outcomes beyond day four or five of the forecast. And we’re going to discuss other risks below. But at this time our land mass of biggest concern is the island of Bermuda. Residents there should be keeping very close tabs on the system.

Other concerns with Erin?

Yes, we have some. Depending on how quickly Erin strengthens (i.e. a slower-to-organize storm would remain further south) we would advise people living in the northeastern rim of Caribbean islands, including Antigua and Barbuda, the Virgin Islands, and Puerto Rico to remain vigilant. These islands are unlikely to see a direct hit from Erin, but they are at risk of higher waves and heavy rainfall beginning late Friday and running through the weekend.

Areas of the US East Coast, such as the Carolinas and Virginias, should also keep an eye on Erin. The risk of a landfall there is very low, but it remains non-zero. More importantly, like the Caribbean islands discussed above, there could be impacts to seas along with heavy rainfall. Overall our concern level for the mainland United States is fairly low, but at a week out we cannot say anything definitive about impacts there.

What about the Gulf?

What about it? I like living there. Good people. Great seafood. This week even the waters near Galveston have even been blue-ish. Oh, you mean the new tropical blob there highlighted by the National Hurricane Center this morning.

Well, I don’t have much to say about this this morning. On one hand, yes, the calendar says it is August. So anything tropical in the Gulf at this time of year raises one’s eyebrows. But I’m having a hard time getting too worked up about a tropical low that will find only marginal conditions for development. If we dig into the ensembles there does not even appear to be too much of rainfall threat. For example, based on the European model, the probability of rainfall amounts of 4 inches or greater is near zero for all but a few isolated areas of Mexico. So yes, we’re going to watch this thing. But no, we’re not going to get too excited about it.

What else?

Overall it’s fairly quiet out there today. We’re watching for some flood concerns in southern Kentucky and Tennessee, including the Great Smoky Mountains area. A flash flood watch is in effect for much of this area, where there could be some training rainfall and higher wind gusts. The threat of heavy rainfall should pass this evening or tonight.

Beyond that, it’s mostly just hot out there in the United States, which is to be expected in August.

In brief: A tropical disturbance will move into the northeastern Gulf a little less than two days from now. Thereafter it should track westward. The most probable outcome is a moderate disturbance moving into Louisiana later this week, with the potential for heavy rainfall. But we will continue to watch things closely to see how the system evolves.

This weekend brought more flooding across parts of the United States. On Saturday evening the Davenport, Iowa area dealt with several inches of rain that flooded some homes and submerged vehicles. By Sunday the flood risk returned to Texas, where a large part of the Texas Hill Country saw a second round of heavy storms, including the previously hard hit Kerrville area. This produced flash flood warnings along and east of Interstate 35, but the strongest of the storms have now moved off to the southwest. Also this weekend there was a devastating fire on the North Rim of the Grand Canyon, which destroyed the historic Grand Canyon Lodge. So all in all, not ideal.

Gulf disturbance

After all of this, we are turning our attention to the tropics this morning. We have been mentioning the possibility of a tropical system developing this week in the Northern Gulf of Mexico for several days, and the National Hurricane Center has now begun highlighting the possibility. As of 8 am ET on Monday, forecasters there give the system a 30 percent chance of becoming a tropical depression or storm this week.

The remnants of a front, currently in the Atlantic Ocean off the coast of Georgia, should move across Florida over the next day or two, and into the northeastern Gulf. Once there, conditions could support the development of this area of low pressure into a depression or tropical storm that would continue moving generally to the west.

As to what happens after this, there is not great clarity in the model guidance. The background conditions, including sea surface temperatures and wind shear, are somewhat favorable for organization and intensification. But this is not an ideal situation, and the system is likely to remain fairly close to land. So we don’t expect this to explode over the deep and warm waters of the Gulf. Eventually it should move toward Louisiana.

One outlier model that appears to be most bullish on the system is the Germany based ICON, which brings a moderate tropical storm toward southern Louisiana by Thursday morning (shown below). Some people may remember that the ICON model is one of the outliers that correctly predicted Hurricane Beryl would impact Texas about a year ago, so we are not completely dismissing it. However, most of our other guidance does not develop a tropical storm, but rather keeps this at a disturbance or a depression level.

So in terms of intensification what we can say right now is that we don’t anticipate a significant wind storm. We cannot rule it out, but high winds and storm surge are not the main talking point. Rather, rainfall potential is.

Precipitation outlook

As this system tracks across the northern Gulf of Mexico, it is likely to bring increased rainfall chances to the Florida Panhandle, southern Alabama and Mississippi, and especially southern Louisiana. For now, NOAA’s Weather Prediction Center has that area, including New Orleans, under a “slight risk” of excessive rainfall next Thursday (shown below) and Friday.

That’s a good starting point, but depending on the evolution of this system that estimate may need to be bumped up in a day or two. The bottom line is that the second half of this week could bring a significant amount of rainfall into Louisiana. Right now we can only monitor the risk, rather than provide a definitive forecast. Hopefully that changes in a day or two.

As for areas further west, including Texas, we cannot rule out impacts at this time. However, none of our reliable guidance shows this system (or its heavy rainfall) tracking far enough to the west to bring heavy rains or winds to Texas. But it is something we will continue to watch.