Matt Lanza

Tropical Storm Erin forms, and the forecast remains mostly the same

In brief: Tropical Storm Erin formed this morning from Invest 97L. It’s expected to make its way north of the islands by the weekend. From there, it’s likely heading out to sea, but we explain why the chance isn’t quite 100 percent. Plus, a quick update on the Gulf, which won’t see development but could see locally heavy rain this week.

Tropical Storm Erin

With our first real significant Atlantic storm of the season now likely getting underway, we’re doing a quick evening post here to just set the landscape up, as I know some people may be a little confused or wondering if things have changed since this morning’s update. In short, they haven’t changed a whole lot.

Tropical Storm Erin is currently expected to stay north of the islands. (NOAA NHC)

Erin has been identified with 45 mph maximum sustained winds just west of the Cabo Verde Islands. It’s hauling westward at over 20 mph. This quick forward speed probably won’t do it many favors over the next day or two, allowing for only gradual intensification, but it should be a slow, steady intensification over the next several days with probably a burst of rapid intensification at some point later this week or weekend. In fact, the intensity forecast for Erin is pretty dang aggressive over the next several days, showing the storm becoming a category 2 to 4 hurricane by the time we get to Friday or Saturday.

Erin will likely gain intensity rather quickly after midweek. (Tropical Tidbits)

The track forecast is in equally decent model agreement, showing a good, tight track consensus through Sunday or Monday, bringing the storm north of the Caribbean islands.

The track forecast for Erin is in strong agreement through the end of the week and probably the weekend too. (Tropical Tidbits)

Thus, the confidence in the NHC forecast shown above should be moderate to higher than usual.

For the Caribbean islands, this is unlikely to impact directly, but folks in Puerto Rico or the Virgin Islands through Anguilla or Barbuda should probably keep tabs on the size of Erin in case fringe impacts are felt in those areas.

After the weekend, Erin’s forecast confidence drops off significantly, as you’d expect from any tropical system in the day 8 to 10 timeframe. But here are a couple thoughts. First, Erin’s quick intensification will likely help it turn more northerly in time. In fact, you can see on the model track forecast spread above a very sharp northwest or even due north turn showing up on days 6 or 7. A stronger Erin would be more apt to feel the weakness in ridging that develops over the western Atlantic late this weekend and early next week. This will more than likely allow it to begin gaining latitude.

The second thing we can say is that history favors an out to sea track, though not at 100 percent. Of the 56 known named storms track within 120 nautical miles of Erin’s forecast position in 24 hours, 51 of them have gone out to sea, a U.S. hit rate of about 9 percent. Of course, Bermuda is on the way out to sea, and that was at least threatened by 7 of these storms as well.

Storms that have historically tracked within 120 nautical miles of Erin’s forecast position tomorrow evening mostly turn out to sea. (NOAA)

So currently modeling, history, and the overall setup we see favors Erin turning out to sea eventually. That said, anytime the storm is 7 to 10 days away from somewhere, you keep an eye on things. But hopefully this allows some folks to breathe a little easier in the meantime.

Gulf blob

Alright, I neglected to really touch on this earlier today, but the Gulf is looking pretty revved up right now. Usually, when you see this, you worry a bit in August. But!

The Gulf is quite busy, but no development is expected. (Weathernerds.org)

There’s a mountain of wind shear in the western Gulf right now, and the eastern Gulf isn’t exactly hospitable right now either. This is just your basic, run of the mill surface trough interacting with warm water and hot, humid Gulf weather, producing lots of thunderstorms, mostly over open water right now.

Rainfall over the next few days could be 1 to 3 inches or more in spots for parts of the Gulf Coast as this trough lifts into and through the Southeast. (Pivotal Weather)

We could see 1 to 3 inches of rain in spots, with isolated higher amounts in excess of 5 inches possible through Wednesday or Thursday as this system lifts into and across the Southeast. More tomorrow!

Invest 97L likely to develop soon but not an urgent concern for land

In brief: Invest 97L should become a tropical depression soon. While there is still plenty of uncertainty in the future, odds still currently favor a system heading out to sea ultimately. We explain more below. The rest of the tropics are ho hum for now. Strong heat in the West will gradually migrate back eastward this week, and we have details on that too.

Invest 97L on the cusp of developing

Our tropical disturbance in the eastern Atlantic is looking relatively healthy this morning, and it’s sitting just north of 15°N latitude. Development odds are up to 90 percent, and it’s entirely possible that we have a tropical depression here before this evening.

Invest 97L may be on the fringe of becoming a depression soon. (Weathernerds.org)

In a bit of an odd twist, weather modeling is actually in really, really good agreement on the general track of Invest 97L over the next 48 to 72 hours. Often in these nascent systems, there is uncertainty around exact location and placement and to some extent track. But in this case, the modeling all seems to be sniffing from the same bowl of food. In fact, you can see that European ensemble and experimental/operational AI ensemble members are all mostly packed together by Wednesday evening east of the islands.

Strong model agreement through 60 to 72 hours. (Google Weather Lab)

From there, the system will continue to track west or west-northwest across the basin arriving probably just northeast of the Leeward and Virgin Islands by late Friday or Saturday. A couple things have sort of changed since yesterday when looking at the upper-level weather pattern around whatever 97L is by Saturday or Sunday.

First, the weakness between high pressure over the Gulf and high pressure over Africa seems to have strengthened a little. This should allow 97L, likely a named storm by the weekend to gain more latitude just northeast of the islands. Historically, most storms end up tracking out to sea from there, perhaps threatening Bermuda on the way. And in this case, that’s still probably the likeliest outcome. However, there is still enough uncertainty around exactly how features orient and what intensity the storm itself has at that point that does keep the Bahamas, East Coast, and Atlantic Canada still in play here.

Invest 97L is likely a tropical storm or stronger this weekend. History suggests it will head out to sea, but there remains enough uncertainty on specifics for others to continue to monitor. (Tropical Tidbits)

But, I will say that at this time at least, the vast majority of ensemble model guidance from both AI and traditional modeling is sweeping this thing out to sea. As always, we will continue to watch and keep you posted on any changes, updates, etc.

Behind Invest 97L

There’s not a whole heck of a lot doing with any specificity right now behind 97L. There is another wave trailing it that may have some chance to develop a little farther south than 97L, but at this time, the AI modeling is most excited by this rather than the traditional ensembles. Some of the newer AI ensemble modeling has proven to be quite overzealous with tropical genesis this season, meaning anytime there’s a remote chance of development, they jump on it too quickly. For now, we’ll see if that next wave does anything, but there are no other urgent or specific concerns we’ve got heading through early next week at this time.

West Coast sizzle will migrate east this week

Ongoing heat in the Western U.S. continues. Portland had their hottest day since last summer yesterday, topping out at 99°, and today should be even a bit hotter.

(NWS Portland)

To the south, Las Vegas hit 110° yesterday, their 3rd hottest of this summer. They’ll come close to their hottest of summer today and tomorrow as well, with highs of 109-111° expected, near records for this time of year. Expect strong heat relative to normal today in Michigan and northern Maine as well. Heading through the week, the focus of heat will gradually shift back toward Florida and the Southeast.

Thursday’s heat risk peaks over Florida with near extreme heat between Tampa and Orlando. (NOAA)

Remember the high pressure system that sort of closes off the Gulf from Invest 97L? Well, it should keep the Gulf out of play from a tropical system, but it’ll definitely make you sweat!

Invest 97L will be the disturbance to watch this week in the Atlantic

In brief: Invest 97L will be the tropical disturbance to watch this week as it marches across the Atlantic. It’s far too soon to say with any certainty how things will play out, but we discuss some of the complicating factors involved in the forecast below. Also, flooding in Milwaukee yesterday and this morning, as we watch a higher-end flash flood risk in southeast Kansas and parts of Missouri.

Good morning. Today we’ll dive back in on the next disturbance, now tagged Invest 97L. Invest 96L in the open central Atlantic is not a concern, so we’ll skip that one today. Plus, another moderate risk (3/4) of flash flooding today, this time in Missouri and Kansas.

Invest 97L

First off, the tropical wave emerging off Africa is now known as Invest 97L. This has been given a 30 percent chance of developing over the next 2 days but an 80 percent chance over the next week.

Invest 97L is up to an 80 percent development chance this week. (NOAA NHC)

We’re now seeing Invest 97L gradually cross the Cabo Verde Islands. This is by far the healthiest looking tropical wave we’ve seen off Africa this summer.

Invest 97L has bucked the trend of tropical waves suffering from a lack of thunderstorms lately. (Weathernerds.org)

Several of the recent tropical waves we’ve seen emerge off Africa have lacked thunderstorms. Invest 97L does not have that issue, and it seems to be spreading some heavy rain across the Cabo Verde Islands today.

Over the next 2 to 3 days, we will see the wave gradually consolidate west of the Cabo Verde Islands and also a little farther to the north. Generally speaking, we should see a consolidated tropical wave attempting to become a depression in about 2 to 3 days, somewhere west of the Cabo Verde Islands and along 15 to 18°N latitude.

About half of the European ensemble shows development of 97L by Tuesday evening. (Weathernerds.org)

Things are fairly straightforward between day 3 and day 5. The disturbance should end up around 500 to 700 miles east northeast of the Leeward Islands by the time we get to later Thursday. From this point, the track forecast gets very, very complicated. To try and sift through this mess, let’s do what we did yesterday and look at the upper pattern. Beginning on Thursday, we can see high pressure still in control to the north of 97L, which should continue to direct it west or west-northwest across the Atlantic. At this point, I would still watch this closely in the northern Leeward Islands, Puerto Rico, and the Virgin Islands.

High pressure over the Atlantic will steer 97L west or west-northwest through late week. (Tropical Tidbits)

As the weekend arrives, the high pressure system in the Atlantic will begin to evolve. For one, it should weaken. As this happens, this will allow 97L to begin to gain some latitude. This is historically a situation where we often see storms intensify, gain latitude, and turn out to sea, possibly threatening Bermuda on the way. But the upper pattern isn’t exactly that straightforward with this one it seems. At least not sitting here a week from then.

By Saturday, 97L is probably north of the islands, and it should begin to gain latitude into a weakness between high pressure over the Gulf and high pressure east of Bermuda. (Tropical Tidbits)

Initially, yes, look for 97L to play by the historical rules of the majority of storms in this situation and start turning more northwest. But there are signs that high pressure near Africa and the Canary Islands will try to build west across the Atlantic early next week. If that happens, that may narrow the escape route for 97L out to sea or at least keep it going more northwest than due north.

So, it remains very complicated. The betting odds would still favor this system turning north and eventually out to sea. However, those odds remain low confidence. Folks from Florida and the Bahamas up the East Coast into Atlantic Canada and Bermuda should still be monitoring this system.

Other things we can say? The intensity of the system will matter, as a weaker one would be more apt to stay farther south, perhaps becoming more of a landfall threat later. A stronger system earlier may be more apt to curve back out to sea more easily. The exact latitude this thing establishes will make a difference too. All these things are connected, and none of them are quite figured out just yet. Look for some gradual clarity on who, if anyone is at relative higher risk over the next 2 to 3 days.

Flash flooding risks persist

Another day, another moderate risk of flash flooding.

Moderate risks of flash flooding (3/4) extend from Wichita to near Kansas City and Mid-Missouri. (NOAA WPC)

Yesterday’s rainfall was impressive, but it ended up a little farther northeast than expected. Some gauges near Milwaukee have received over 10 inches of rainfall since yesterday morning, with another round of heavy rain pushing in as I type this. The rain ended the Wisconsin State Fair a day early.

Rain totals of 7 to 10 inches fell around Milwaukee yesterday. (NOAA)

It would seem an additional 1 to 3 inches of rain is possible there this morning, with some additional rain chances later today.

Meanwhile, in the moderate risk area, a line of thunderstorms is crossing Kansas and the KC metro now. Additional heavy rain development seems likely this afternoon and evening, especially south and east of I-35.

HREF model shows heavy rain risk highest in southeast Kansas and to a lesser extent in Missouri. But with a moderate risk in place there, it’ll be important for all areas keep tabs on rainfall today. (NOAA SPC)

Flash flooding risk continues tomorrow just off to the east of today’s risk area.

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.