Modest Atlantic development possible, while Mario will aid in SoCal storm chances later this week

In brief: The tropical wave in the central Atlantic is becoming more likely to develop over the next few days as it moves west northwest across the Atlantic. No land concerns are expected right now. Meanwhile, Pacific Tropical Storm Mario is likely to spread thunderstorm chances across Southern California later this week. We also check in on the Dakotas which had a mini tornado outbreak on Sunday.

Atlantic tropical wave

The wave we’ve been talking about since last week in the middle of the Atlantic looks pretty decent this morning. It’s certainly better looking than the previous wave we were tracking out there.

An Atlantic tropical wave is now up to 80 percent odds of developing. (Weathernerds.org)

This wave now has 80 percent odds of development per the NHC, and I imagine this will get tagged as an Invest within the next day or so. Whereas the previous wave we tracked out here had high development odds and failed to make it, this one has much less of an “all or nothing” chance to develop. There is strong model agreement in some development by as early as Wednesday or Thursday (shown).

Strong model agreement that by mid to late week we have a tropical depression forming in the central Atlantic. (Google Weather Lab)

Notice that this system is already at a fairly moderate latitude by mid to late this week, and with it continuing west northwest, we should see this pass fairly well north of the Caribbean islands. From there, it seems as though it will either curve back north and northeast out to sea, or it will continue west northwest to the north of the islands, sort of in the fashion of Hurricane Erin earlier this season, particularly if it’s on the weaker end of the spectrum. The most likely outcome is some loosely organized storm turning out to sea. But for folks in Bermuda, it probably makes sense to keep a side eye on this one through the week, unlikely as it would be to impact the island.

Generally speaking, while this is the most interesting item we’ve had in what seems like weeks in the Atlantic, it’s thankfully not a serious land threat at this point.

What’s next in the Atlantic?

The background state of the Atlantic may revert back to hostile again after about September 20th, meaning that we’re probably going to continue to see systems struggling for the end of September. Probabilities for tropical development are not exactly strong looking outside of that one tropical disturbance in the middle of the Atlantic.

ECMWF Weekly model odds of tropical cyclones for the end of September showing generally below average development odds beyond the central Atlantic wave. (ECMWF)

In fact, if anything, they’re below average off Africa and below average off the Southeast coast. I do suspect we’ll begin to see more noise in the southwest Gulf or western Caribbean, as is typical for late September and October, but aside from that, it’s becoming apparent that this is probably going to end up being one of the more subdued hurricane seasons in recent memory. Of course, one bad outcome in early to mid-October can change the whole perception, but we currently don’t see anything else out there.

Tropical Storm Mario

(Wholesale Auto Plates)

In the Pacific, Tropical Storm Mario was declared dissipated this weekend, but it turns out the princess was just in another castle. So, Mario is back to life.

(NOAA NHC)

Mario should continue off to the northwest, eventually succumbing to King Koolpa, as sharply cooler water awaits it to the north.

Mario’s tracks from various models plus water temperatures turning sharply cooler after the next 24 hours. (CyclonicWx)

So why am I taking up virtual oxygen talking about a storm that will remain offshore and dissipate. Besides the ability to add Mario puns to the post, the moisture from Mario is going to play a role in the weather in California later this week, with showers and thunderstorms likely to infiltrate from the south, particularly in SoCal. In addition to the potential for locally heavy rainfall in Southern California, there could also be some isolated dry lightning issues with respect to fire starts in parts of the interior. The entire region is under a marginal (1/4) risk for locally heavy rainfall on Thursday.

Some locally heavy rain in addition to dry lightning concerns will permeate SoCal later this week. (NOAA WPC)

Rainfall amounts will be minimal in most places, but there will be areas that see a solid half-inch to 2 inches of rain, which could cause some flash flooding in spots.

North Dakota ‘naders

Quite a day yesterday in the Dakotas. Historically, not a tornado-prone location in September (there have been only one or two historical noted reports of tornadoes in this corridor of the Dakotas since at least 1950 in September), there were nearly 20 reports of tornadoes on Sunday from at least 4 tornadoes. Reports ranged from near Mobridge, SD through Bowman, ND, Golden Valley County, and Hettinger, ND.

(NWS Bismarck)

The National Weather Service office in Bismarck is looking for reports from yesterday across the corridor in northwest South Dakota and western North Dakota. Certainly, there were a number of chasers on these storms. But overall, this was a bit of an impressive, somewhat surprising September event this far north.

Development odds increasing with next Atlantic wave, but concerns for impacts are not increasing

In brief: The tropical Atlantic has a number of items but only one really with a chance to develop much. No threats to land at this point either. Aside from that, there’s not a whole lot to say right now through about the 25th. Heavy rain and flooding chances visit South Florida and the southern Rockies today and tomorrow.

Atlantic tropics

The satellite picture over the Atlantic looks pretty noisy, but in reality only one item is truly a development candidate.

The Atlantic is noisy but not busy. (College of DuPage)

There is a cool front draped from near Florida into the Atlantic. You always watch these sorts of boundaries for any development, but there’s nothing imminent, and anything would likely track east or northeast out to sea. The big area of storms you see over the central Atlantic is an upper-level low pressure system, so that won’t develop. There’s an active tropical wave moving into the Lesser Antilles today, bringing some showers and storms but no development odds. And then there’s a broad tropical wave in the eastern Atlantic off Africa that’s now up to 40 percent odds of development as it moves into the open Atlantic this weekend and next week.

Odds of development are slowly increasing in the eastern Atlantic. (NOAA NHC)

There is decent model support still for this to develop, and this wave will have a slightly more supportive background state in the Atlantic to work with as it moves west and west-northwest heading toward next week. This is probably a more legitimate candidate to develop than Invest 91L was a week or two ago. That said, it too will be fighting both dry air and wind shear in its neighborhood as it comes across. For now, I would not expect quick, strong development, but as has been the case with almost every system this year, a slow, uneven development pace. Not much has changed in terms of track, as Eric showed yesterday. We’ll keep watching, but at this point, this system is not a real serious concern.

Beyond that, who is next? Great question. We are seeing noise from the GFS model beginning to stir up the Central American Gyre (CAG) late in the period. That’s a climatological quirk of the model, where it tends to gravitate toward development in that region, whether realistic or not. In this case, there’s not a whole lot we can truly say. If you go by the Euro ensemble (like below), you see that surface pressure is currently forecast to be higher than normal, typically not a signal for development.

The Euro ensemble currently shows generally higher than usual surface pressure in the CAG and Caribbean regions after day 10, which would indicate lower than usual tropical development chances. (Tropical Tidbits)

But that’s 12 to 13 days away, so a lot can change. The main takeaway for me as a forecaster right now? There’s not a particularly strong signal for anything else through September 25th. We’ll see if that continues.

Flood chances

Elsewhere, not a whole lot to discuss weather-wise right now. There is some flash flood risk both in South Florida and in the Southern Rockies today.

(NWS Miami)

In Florida, showers and storms will move along slowly the next couple days, bringing a chance for as much as 3 to 4 inches of rain in spots in a worst-case scenario.

In the West, the risk is on burn scars in particular, with scattered showers and storms likely today and tomorrow across southern Colorado and New Mexico, where flood watches are posted.

(NWS Albuquerque)

The heavier rain risk shifts into the Plains this weekend.

Taking stock of the Atlantic season so far, and looking ahead to the next wave of interest

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.

Total ACE for the Atlantic this season, through Wednesday. (cyclonicwx.com)

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.

Seven-day tropical outlook from the National Hurricane Center.

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.

A smattering of AI and the ECMWF model predict the location of the tropical wave by next Wednesday. (Google Weather Lab)

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.

Odds of a tropical depression forming in a given location over the next 10 days. (ECMWF)

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.

As we hit the statistical peak of hurricane season, we find ourselves in a weird position

In brief: Why is the tropical Atlantic hitting the historical peak of activity with not a wave to be found? We explain the details below, but it looks quiet for the next 7 to 10 days. Beyond that, risks will surely increase a little but how much so remains a topic of uncertainty.

Happy Tuesday evening everyone. Late today due to participation in the National Weather Association’s 50th anniversary meeting in Huntsville, Alabama, a fine city. But I wanted to catch you up on the historical peak of hurricane season.

Tropics outlook

The next 7 days look quiet. (NOAA NHC)

The outlook is the “not stonks” meme for those of you familiar with internet culture.

I mean, truly, it’s just quiet as could be. Now, it does appear we may get a wave in about 7 days in the open Atlantic that could develop. But that’s the only game in town for the next 10 days it would appear.

The next wave will emerge off Africa in a few days and may develop in 7 to 9 days in the open Atlantic. (Weathernerds.org)

An upper low in the central Atlantic, known as a “TUTT” is imparting shear on basically anything that comes off Africa, so they instantly hit a hostile environment. Additionally, there is a lot of drier air in the open Atlantic, which is not helping anything. TUTT lows drag down drier air from the subtropics into the tropics. A lack of instability, drier air, and shear are all decimating any chance at development right now. Climatology is as good a guide as anything when you look at seasonal predictability and timeframes for activity, but if the key ingredients aren’t there, they aren’t there. The cookbook recipe may say that the cake needs flour, butter, and eggs. But if you leave the flour and butter out, you aren’t baking a cake using that recipe.

Strong wind shear is hampering development, in addition to other factors. (Tropical Tidbits)

In addition to this, in the western Atlantic there is high wind shear as well. So we have a number of highly problematic factors right now as it relates to tropical development. Good for almost everyone!

Now, after 10 days the forecast in the Atlantic seems to favor a slightly more favorable shift for tropical activity. At least we should see more instability out there. That being said, I have seen a couple instances this hurricane season where tropical Atlantic conditions were expected to become more favorable “in 10 to 14 days,” and those conditions ultimately never materialize. That could be true here too. But given our streak of good luck, one figures it can only last so long. At the least, we will probably start to see GFS operational model runs showing tropical development in the Caribbean or Gulf soon. Please remember that this model has a very well-known bias to overdo that activity in most cases, particularly beginning in later September and October, as well as in May and June.

Bottom line: Enjoy the respite from peak season activity. But we still have about half the season’s activity in front of us historically. We’ll keep you posted.