Matt Lanza

The next tropical wave bears watching but the possibilities are all over the place

In brief: Invest 96L is not a concern for land. The wave behind does bear watching for much of the Atlantic basin, and today’s post walks through the process over the next 5 to 7 days. Back on land, more serious flooding risks are in the cards today for Iowa and Wisconsin in particular.

Happy Saturday! Let’s get you caught up on all things tropics and flooding.

Invest 96L

It’s been an interesting ride for Invest 96L. Once the darling of some weather models in the open Atlantic, support for development of this one has floundered for now.

Invest 96L has thunderstorms but little to no organization right now. (Tropical Tidbits)

Over the next few days, 96L is going to turn northwest or northward into the open Atlantic. More than likely, it will head out to sea, though a couple models do kind of keep some fingerprint of the system hanging around in the central Atlantic for a bit. Either way, this one is not a concern for land, and it is unlikely to really develop much, if at all.

Next tropical wave

The National Hurricane Center added an area of interest yesterday for the tropical wave that is emerging off Africa this weekend. No development is expected initially, but by next week, development is becoming increasingly likely.

40% odds of development are noted from the tropical wave emerging off Africa, a percentage that will probably further increase this weekend. (NOAA NHC)

Many of you have been monitoring the progress of this one since earlier this week, as modeling has been periodically going ballistic with development once in the western Atlantic. Let’s focus on what we can actually realistically discuss first, then we can talk about what comes next.

First, the wave emerging off Africa has what you’d want to see from a tropical wave that may develop. It’s got thunderstorm activity. There’s a whiff of “spin” evident. Modeling shows a good deal of mid-level vorticity as it is emerging. Basically, it’s the initial seeds you’d want to see for a development candidate.

The suspect area emerging in the Atlantic on Saturday morning. (Weathernerds.org)

Over the next 2 to 3 days, the wave will continue to march west, eventually passing the Cabo Verde Islands (which may see some hefty rainfall) and settling just west of there. Interestingly, this wave is emerging around 9 to 10 degrees North latitude, but it probably won’t establish itself before curling a little to the north, up around 15 degrees or so North. This is somewhat important information for the rest of the system’s life, as where it establishes latitudinally could play a role in ultimately where it goes. For example, in the western Gulf, it would be exceptionally rare for a Cabo Verde storm establishing north of about 13°N to make it there. Ike was the one exception to that rule in 2008, so it serves as a reminder that rules are made to be broken, but the odds would not favor that part of the world if this is indeed where this wave establishes.

By Monday evening, we should expect to see at least a tropical wave setup north of 15°N, with only slight chances it has formed into a depression yet.

The next tropical wave will establish west of the Cabo Verde Islands by Monday evening. (Weathernerds.org)

Heading out to day 5, we still don’t see a ton of development with this one, but we see a pretty strong signal over the central Atlantic, east northeast of the Lesser Antilles.

Various ensemble members from the European model and AI models show pretty good overall agreement in a general location east northeast of the Lesser Antilles by Wednesday evening. (Google Weather Lab)

There are still a number of differences in placement, speed, etc. that we can’t quite resolve yet, but the general trend is pretty much in okay agreement through day 5. From this point, let’s look at the upper pattern.

The overall setup of the upper pattern that may steer the disturbance around midweek next week. (Tropical Tidbits)

Initially, the disturbance will be steered around the base of high pressure east of Bermuda. This should allow it to turn more west-northwest or northwest even by mid to late next week. However, high pressure over Florida may flex later next week, which could jam up the disturbance just northeast of the Leeward Islands and Virgin Islands. Particularly if this remains fairly weak through late week, this would be the case.

From this point, it becomes a little more difficult to project where the disturbance goes. High pressure may retreat into the western Gulf by next weekend, which may open the exit door back up, allowing the system to head out to sea. Or if it holds a little firmer and longer, we could see the system get closer to the Bahamas or Florida. Or perhaps it turns north and threatens Bermuda. Or it could drift closer to the East Coast. There are many, many possibilities beyond day 5-7 right now. European ensemble member solutions range from something near Hispaniola or the Bahamas to something already halfway to Europe out to sea. There are just a ton of options out there.

So, what can we say right now? We expect a disturbance to pass the Cabo Verde Islands by Monday. From there, it will come west across the Atlantic, settling about 1,000 miles east of the Leeward Islands by Wednesday. Limited development is expected through Wednesday. From that point, the upper pattern suggests a slower movement that may adjust the disturbance some. Beyond day 7, the forecast turns sharply chaotic with numerous possibilities, intensities, locations, and tracks. Folks from the Caribbean up the East Coast and out to Bermuda should continue to monitor the progress of this tropical wave over the coming days.

Iowa and Wisconsin flooding risks

Hey, remember when I said we finally broke the streak of days without a “slight” risk of excessive rain and flooding earlier this week? Yeah, that was incorrect. A slight risk (2/4) was issued later that day. So the streak continues. And today, it’s a moderate risk (3/4).

A moderate risk (3/4) exists for flooding in much of eastern Iowa into southwest Wisconsin today. (NOAA WPC)

Heavy rainfall is moving eastward this morning across Wisconsin, as well as northern Iowa. Additional heavy rain is falling in southern Iowa.

Heavy rainfall is already underway in the Upper Midwest. (College of DuPage)

As the day progresses, heavy rain will march east, new heavy rain will follow, and rain amounts of 3 to 5 inches and locally higher amounts are possible across eastern Iowa and southwest Wisconsin.

(NWS Quad Cities)

Some parts of Iowa have seen 3 to 6 inches or more over the last 2 weeks, so the ground is already primed for flooding here, especially in southeast Iowa. Folks in that region should use caution today and tonight.

A reminder that hurricane season is a marathon, not a sprint

In brief: I’m pushing out a brief post this morning to highlight what I wrote to our Houston audience earlier. This applies to the system coming toward the western Atlantic next week, currently not highlighted by the NHC. We’ll have more on this for you this weekend. Thanks for your support!

It’s a marathon, not a sprint

It’s getting to be the time of year where we do start watching more and more things, even some of the innocuous looking ones. We’ve had some deterministic (operational) model guidance (the GFS, the Euro, etc.) go crazy in the day 14 to 16 timeframe lately. This bears repeating. The day 14 to 16 timeframe. Deterministic modeling has virtually no skill at that timeframe. So, while we are certainly empathetic to people getting a little unnerved when they see bad things in that timeframe, Eric and I both are realists and recognize that those runs, even if 2 or 3 in a row show something similar, are somewhat meaningless. Put another way, if I had a buck for every time a deterministic model wrecked a major Gulf Coast city on days 14 to 16, I’d be getting wrecked on some tropical island somewhere far, far away living the dream. I’m just saying!

So what do we do instead? We look at ensemble guidance for clues. What can the ensembles tell us about the potential for a tropical system in a more distant timeframe? Ensemble modeling is where you take a single model and run it 30 to 50 times but tweak the initial conditions, or what the model starts from. We can’t get a perfect snapshot of the entire atmosphere over the entire globe, so we have to improvise a little. Ensemble guidance is that improv.

Okay, let me show you a perfect example of this. Here’s last night’s GFS operational model for hour 294, which is day 13.

Last night’s operational GFS model shows a major storm near Florida on day 13. (Pivotal Weather)

That’ll get your attention! And it has been showing this for a few days, though it varies in location between the Caribbean, the Carolinas, and out to sea. But what do the ensembles show?

Zero agreement on track or intensity of system on day 13 per the 30+ GFS ensemble members. (Weathernerds.org)

Not all lines on a spaghetti plot chart are created equal. Some of the lines above may be ensemble members that are slightly more skilled than others. That’s a tough lift to figure out specifically in every situation. But the point is this: Yes, the GFS operational model may be right! But according to the ensembles there are a bunch of other options too, including many that go out to sea and a handful that come into the Gulf.

I show you this for a couple reasons. First, I want you to recognize that the scary images you often see on social media are almost always from operational models. Second, when you look at the ensemble guidance, it offers a far more nuanced take on all this that suggests the operational models are just one possible solution of many. We go through this exercise every season. It’s the same culprits from the same places with the same intentions. They’re basically preying on people’s fears to drive engagement under the guise of “we’re not saying this is a forecast (it is), but we want to just let you know what’s out there!” In reality, the picture is nuanced, complex, and not at all straightforward. A deterministic model showing Armageddon on day 13 does not make that scenario any more likely than any of the possible outcomes on the ensemble chart I showed you above. Hurricane season is a months’ long marathon. We just want you to keep your sanity.

In this specific situation: Yes, we should keep an eye on this tropical wave as it comes west over the next 10 days. It is August, and we should keep an eye on all tropical waves this time of year. If it looks like this will be a real, credible threat, we’ll be talking about it here well before it happens. We already have been. But we won’t share scareicane nonsense with you. Thanks for reading!

Busy Atlantic without big risks for now, but we realistically speculate on what happens next

In brief: None of the currently highlighted areas in the Atlantic will threaten land. We discuss some of the speculation surrounding what may come next in the Atlantic, which is probably something of note but what exactly that is is very much TBD. Also, today is the first day since mid-June without a level 2 or higher risk of flooding somewhere in the U.S., ending a remarkable and painful 46-day streak.

The current trio

We’ve seen few changes in the overall expectation that the current three systems highlighted in the Atlantic are unlikely to be threats to land.

Disturbance off the Carolinas

Good news overall. The system off the Carolina coast has not shown any further signs of development, and it appears that its best chance to do so will be on exit from the East Coast as it generally follows Dexter’s path out to sea.

There’s just not much doing off the coast of the Carolinas. (Weathernerds.org)

Development odds have been reduced to 30 percent here as the system exits stage right. At this point there is no sign that this will impact land as it moves away. It could meander a little for a couple days south of Atlantic Canada but it currently looks to be far enough away to avoid any impacts.

Invest 96L in the deep Atlantic

Invest 96L has a few thunderstorms but little organization whatsoever. (Weathernerds.org)

The Atlantic wave got tagged as Invest 96L today, so now we can see some additional forecast data on this in the coming days. Currently, there’s not much to this. But models do indicate that in the coming days, we will see some development. It’s expected to continue to move somewhere between west-northwest and due northwest, which should keep it well north of the Caribbean islands. From there, it still seems likely to find the escape route north and northeast out to sea. Odds of development are 60 percent but odds of land impacts are close to zero at this time.

Tropical Storm Dexter clinging to life

Dexter will likely turn extratropical by this afternoon as it races out to sea. The transition to extratropical just means that it’s no longer deriving its energy from the warmer water and tropical processes. Rather, it’s now behaving more like a nor’easter and being driven by other meteorological processes, acquiring fronts, etc. In the case of Dexter, it is likely to become a hurricane-force non-tropical low pressure, or essentially a major cyclone over the open ocean that isn’t a tropical system. Hazardous for shipping, may produce some rough seas off Newfoundland but nothing more than that.

Dexter is showing signs of a cold front trailing on the south side of the storm, a tell-tale signal that a tropical system is beginning to transition into an extratropical one. (Tropical Tidbits)

Dexter should eventually end up absorbed into a system or two approaching Europe next week, unlikely to produce any major impacts there.

Speculating on the Atlantic’s future

We’re starting to notice the “churn” in comments, posts, questions, etc. that usually begins to happen in August. Much of it focuses on what this model or that model did during a specific run. Yesterday’s fun and games came courtesy of the evening GFS operational model, as it often does (earning it the nickname the “happy hour run”), which decided that one storm wasn’t enough, so it would plant two of them on either side of Florida on day 16. Look, you do you in terms of looking at weather data, but the GFS operational beyond day 10 is virtually useless. So, I’m going to pretend that never happened.

However…

There is good reason to think that we could have something a little more interesting by the time we get to the late forecast period. This would be more in the August 20th-ish timeframe. You can see this by looking at the European model ensemble spaghetti plot. Again, these aren’t answer keys, but rather they’re showing you what each of the 51 ensemble members is doing with a specific system. Each ensemble member is tweaked just a little to create the real uncertainty that exists in the atmosphere at any given moment due to observational capabilities and thus each ensemble member produces a unique outcome. Within that “noise,” occasionally you can derive a signal to push your confidence one way or another.

Of the European ensemble’s 51 members about 60 percent show a developing system in the main development region next week but have absolutely no agreement on exactly where this occurs. (Weathernerds.org)

In this case, we have a strong signal showing up for a system, but its track representation and intensity representation lives in a sea of noise. So what we can say with authority today is that conditions may be favorable for this tropical wave emerging off Africa in a couple days to perhaps become a development candidate somewhere in the Atlantic or Caribbean about 6 to 10 days from now. In fact, yesterday’s European weekly tropical cyclone anomaly chart does show slightly above normal chances for a system in the southwest Atlantic in week 2 (Aug 18-25).

Slightly above normal odds of a tropical system exist in the southwest Atlantic around the August 20th-ish timeframe. (ECMWF)

All this says is that there’s a slightly better chance than usual that a system could end up somewhere in the southwest Atlantic. We can corroborate this with the traditional model ensembles, as both the Euro and GFS ensembles show at least some noise in this general area. There also seems to be some AI model agreement on this as well.

All we can say definitively today is that the next wave emerging off Africa is creating some noise in model runs that make it an area we’ll probably be watching for several days. We have no idea where it’s heading or what shape it will be in when it gets there, and it doesn’t make sense to even begin to speculate on that topic. What we can do is remind folks that it’s the ramp up to peak hurricane season now, and with quiet conditions this weekend, perhaps it’s a good time to review your kits, checklists, etc. and ensure you are prepared in case this is the year for you. We’ll let you know what we know when we know it.

Lowest flooding risk in weeks

Today is the first day since June 21st that the Weather Prediction Center’s excessive rainfall outlook has not had a level 2 (slight) or higher risk. 46 straight days of slight risks or worse. If it’s not a record, it’s close.

(Iowa State Environmental Mesonet)

We will have much more to say about flooding and risks and all that eventually. I wrote a bit about flash flood warnings on my personal Substack yesterday. But I hope the folks at the Weather Prediction Center can catch their breath for a couple days now. Remarkable summer.

Lots of Atlantic noise but virtually all of it over the open ocean

In brief: A disturbance off the Carolina coast has a 40 percent chance to develop heading into the weekend, but it looks to remain offshore. Tropical Storm Dexter may intensify over the open Atlantic as it transitions from tropical to non-tropical late this week, no threat to land. The area in the deep Atlantic with 60 percent development odds remains worth watching but not likely to stir up too much trouble.

Tropical Atlantic

We’ll continue our daily check up on the areas worth watching in the tropical Atlantic — and speculate on what could come next.

Carolina coast

Starting closest to land today, some good news. The disturbance that’s expected to attempt to develop off the coast of the Carolinas appears that it will be less stuck than it appeared earlier in the week. Again this morning, there just isn’t a whole lot there yet.

The area we’re watching off the Carolinas is void of much of anything still today. (Weathernerds.org)

Initially, the thought was that we’d see development gradually through the week, followed by a very slow-moving or stationary type system off the coast. The first half of that statement is still true. Development will be very sluggish here. We won’t wake up to a tropical storm out of nowhere tomorrow. It may not be until Friday or Saturday that we see anything make a real effort to form. And from there, it now looks as though it will slowly but steadily move north and northeast, heading out to sea. Development odds have been pushed back to 40 percent this morning, indicating that this is not exactly expected to really get going once it does start to attempt development.

5-day rainfall totals peak at 3 to 5 inches near Myrtle Beach, with a widespread 2 to 4 inches between Cape Lookout and Florida. (Pivotal Weather)

In terms of impacts: Rainfall and rip currents are at the top of the list. You can see the 5-day forecast average rain totals above. Locally higher amounts are possible, especially today in interior North Carolina and Georgia, where flood watches are in effect.

You can see a broad slight risk (2/4) posted from the Piedmont south to the Georgia coast for today for heavy rain and flooding. (NOAA WPC)

A lot of the rain is actually front-loaded and not directly related to the system itself, but the whole pattern is connected. Rip current risk is moderate to high on the North Carolina coast, and if any development does actually occur offshore, that risk will hold into the weekend. Just something to be aware of if you’re beaching it this weekend in the Mid-Atlantic or Southeast.

Tropical Storm Dexter

Dexter continues to cling to life as it moves out to sea.

(NOAA/NHC)

Dexter is expected to become post-tropical tomorrow and end up north of the Azores by Sunday as a non-tropical low pressure. From there, Dexter’s remnants end up getting tied into a storm system near or north of the British Isles by Tuesday or Wednesday of next week. No big impacts are expected right now.

Tropical Storm Dexter has a lopsided appearance today. (Tropical Tidbits)

Dexter’s thunderstorms have outpaced the system itself, with the center again almost exposed entirely this morning. That’s a sign of an unhealthy storm. It’s just not in the greatest environment right now, packed with wind shear. That said, tropical systems have a funny way of doing things when they transition to extratropical systems. In Dexter’s case, while it may continue to look very sloppy, it’s likely to increase in intensity, with winds possibly approaching hurricane-force at some point in the next couple days. Thankfully that will remain over the water, though some rough seas could be generated in Atlantic Canada.

Deep Atlantic

We are watching two areas in the Atlantic. There is the one being highlighted by the NHC with a 60 percent chance of development. There is also what will probably be the next highlighted area by the NHC in a day or two.

The tropical wave associated with 60% odds of development looks a bit better this morning, while the next wave emerges off Africa behind it. (Weathernerds.org)

The 60% area looks a good deal better this morning than it has the last couple of days. We will probably see some gradual organization attempt to occur from this one between now and Friday. I wouldn’t be shocked if the 60 percent becomes a 70 or so by later today. In terms of this one’s future, it will probably have a relatively low ceiling for intensity. But a depression or tropical storm seems like a decent possibility at this time.

As the system moves, it will be steered west northwest or even northwest at times around the periphery of high pressure in the eastern Atlantic. By the time it gets to the weekend, high pressure may strengthen somewhat and force to turn back more to the west for a short time. Eventually, it will likely hit the escape hatch and get drawn back northwest and north through a weakness in the high pressure across the basin.

The system in the Atlantic will be steered around high pressure in the middle of the Atlantic, but it should find a weakness in the pattern by early next week, allowing it to escape north and eventually out to sea. (Tropical Tidbits)

This should allow the system to ultimately turn out to sea. I would say it’s probably worth continuing to monitor for the Caribbean or Southeast or Bermuda, but it’s unlikely to stir up too much trouble.

On the image atop this section, I did highlight the area behind this disturbance as one to watch as well. Model guidance keeps this one a little more southward in the Basin, which could in theory allow it to get closer to more land in 10 to 12 days. There is very little consensus on this one yet though, so for now it’s just probably the next area we’ll watch but nothing more than that.