Erin remains a tropical storm as its long-term path comes into better focus

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.

Tropical Storm Erin is still facing some challenges this morning. (NOAA)

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.

Super-ensemble forecast for Tropical Storm Erin. (Tomer Burg)

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.

Blobby McBlobface comes to the Gulf. (National Hurricane Center)

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.

Tropical Storm Erin chugging westward, but struggling to maintain thunderstorms this morning

In brief: Tropical Storm Erin is struggling this morning due to dry air, which may impact its track some over the next 3 to 4 days. While Erin should still eventually turn out to sea, folks in the northeast Caribbean will want to monitor the storm’s progress closely this week, and those on the East Coast should continue to just keep tabs on any further changes for the time being.

Tropical Storm Erin

This morning, Erin has pressed pause on intensification as a lot of the deeper thunderstorms surrounding the storm seem to have faded away. We figured Erin would struggle a little in the first couple days, but this is a fairly substantial drop off in storm activity.

Erin’s thunderstorms have weakened, though it still has a well defined circulation. (Weathernerds.org)

One reason for the diminished look of Erin this morning is likely a healthy amount of dry air that sits in the mid-levels of the atmosphere around the northern and western flank of the storm.

Erin is battling dry air right now. (Tropical Tidbits)

Hurricanes and tropical storms need warm water, low wind shear, and moisture to thrive. Absent one of those ingredients and you probably get a sloppy outcome. Indeed, this is where we are right now.

So, what does this mean going forward? Well, if you look at Erin’s forecast track from the NHC today, it has indeed shifted a bit farther south.

(NOAA NHC)

It hasn’t shifted dramatically so, but it has shifted enough to be noticeable. This is likely because Erin’s intensification timeline has slowed down a little. Less intense storms will track a little farther south and be less apt to turn poleward (north) quickly. One of the challenges in determining the forecast track of Erin over the next several days will end up being how much dry air it has to fight off. If you look at the envelope of track possibilities through Friday evening, at least based on the European and GFS ensembles, you do see a somewhat healthy spread in possibilities opening up. Since yesterday, this has shifted a couple hundred miles south

A comparison of Monday vs Tuesday morning’s ensemble guidance on Erin shows a slight southward drift in forecast track. (Tomer Burg)

This is not a dramatic change, but when you do the virtual math here, there has definitely been a trend toward a slightly weaker system, slightly farther south. Also notice a slight bend to the west-southwest that shows up on those maps as Erin tracks west of about 55°W longitude. It’s a minor difference, but for the islands, it could have some implications.

So what does this mean going forward? Well, in the near-term it doesn’t mean much of anything. Erin will probably continue to struggle a bit until it can insulate itself from the dry air that surrounds it or shake it off entirely. This could mean that we see an additional trend to the south of Erin’s track today, perhaps getting a bit closer than some would like to the islands. On the flip side, if Erin struggles more, it would be less likely to approach the islands as a hurricane. So you have to balance the bad with the good.

Still, once it nears the islands, the overall environment is expected to improve, allowing for Erin to intensify, turn north, and scoot out to sea, though Bermuda bears close watching of course in that scenario. All that said, I think there’s at least some evidence today that while the environment around Erin is expected to improve and allow for strengthening, that doesn’t necessarily mean it will. So folks in the northeast Leeward Islands, Virgin Islands, and Puerto Rico should continue to monitor Erin’s progress closely over the coming days.

For folks on the East Coast? Generally speaking, nothing has changed with respect to the risk profile there. Erin is still expected to turn out to sea, as the break in ridging over the Atlantic persists. As soon as Erin begins to intensify, it should begin to gain latitude and eventually turn back northeast. That turn looks a little more like a J-turn today than a U-turn, but the end result would be the same. All that said, the subtle changes we’ve seen since yesterday are a good reminder to never take a hurricane forecast as a given 7 to 10 days out. Continue to monitor Erin’s progress in the coming days.

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!