Matt Lanza

September 28, 2023 Outlook: Complex interactions between Philippe and 91L complicate the Atlantic forecast some

One-sentence summary

A complex interaction between Philippe and Invest 91L enhances a bit of uncertainty in the Atlantic next week as it relates to the islands, though most outcomes still favor minimal impacts in Puerto Rico, the Virgin Islands, and Lesser Antilles.

Happening Now: Philippe and 91L (future Rina?) and where will they go?

Looking at satellite this morning, the Atlantic is just jammed up with Tropical Storm Philippe and Invest 91L back to back. Personal space anyone?

Tropical Storm Philippe and Invest 91L are basically adjacent to each other, and at some point something will need to give in terms of which of these becomes the “big dog” of the Atlantic pack. (Weathernerds.org)

Anyway, this is actually important context to start today’s discussion with because the future and the future of any impacts will be somewhat contingent on which of these two becomes the dominant system in the Atlantic. On one side you have the GFS model, which has tended to overdo Philippe’s actual intensity, meaning that it has tended to slow it, park it as 91L interacts with it, and then take it north into the open ocean as a hurricane. The Euro essentially kills off Philippe and then sheds its remnants in the islands with some rain, while 91L tracks west as a weak system before turning north and strengthening.

Confidence in Philippe’s track is high until it gets just north of Anguilla, and then all bets are off. (Tomer Burg)

Interestingly, the setup here is one that seems to keep in play a Fujiwhara interaction between the two systems. What is that? Basically, the two systems would track close enough to one another to impact each other’s track. In this case Philippe would likely slow, stall, or get pushed to the south since it’s ahead of 91L, and 91L would basically slingshot over the top of Philippe either west or northwest and out to sea. The GFS operational model shows this quite well.

Philippe (at right) may slow or stall while 91L “slingshots” off to the west or northwest. Once that interaction untangles, Philippe would be free to turn north. (Tropical Tidbits)

In most possible outcomes, impacts to the islands are not exactly serious, so let’s make that abundantly clear. The arithmetic here is that if 91L (or as the GFS says, Philippe) ever explodes in intensity, it will “feel” upper level steering and turn north out to sea. Is there a chance that the system stays weak, tracks into the islands, and then blows up? I suppose that’s possible, but if it gets to that point, the theory would be that dry air or land interaction limit a lot of upside. So for folks in Puerto Rico or the islands, it would be unlikely that this is a major noisemaker as it comes in. We’ll continue to watch this, but for now the thinking is that it will just be an annoyance out there more than anything. Presumably if one of them does develop into a hurricane and turns out to sea it would happen east of Bermuda. We’ll keep watch and let you know if anything changes.

The medium-range (days 6 to 10): Noise off the East Coast?

We’re starting to get some sort of idea as to what might come next. Models have been consistently showing some sort of upper low or storminess between the southeast Gulf and off the North Carolina coast next week, but they have been wildly different run to run on details. The forecast idea today seems to be honing in on an upper low developing off the Carolina coast before a piece of it drifts southward toward or off the coast of Florida. Another lower-end system could theoretically develop from this, though the odds are fairly low.

The upper level map from the European model for next Monday shows the upper low exiting off the East Coast, with just enough “spin” (or vorticity) left behind to linger off the coast, unlikely to develop but worth watching. (Tropical Tidbits)

This probably means minimal impacts right now beyond rough surf and rip currents. But this is probably at least worth keeping a side eye on.

Fantasyland (beyond day 10): Still no substance to any threats

We’ve been saying that it may be wise to keep an eye on the northwest Caribbean or eastern Gulf in the late period all week. We continue to be faced with a weather map that does not really show any specific threats; just some noise. So I have no reason to believe that something *will* happen beyond day 10, but I also know that the big picture in the atmosphere doesn’t completely shut the door on that potential. We’ll keep watch.

September 26, 2023 Outlook: Beyond Philippe and Invest 91L riding its coattails, it’s tough to make much of anything else

One-sentence summary

Tropical Storm Philippe and Invest 91L in the Atlantic remain no serious concern at this time, and while things look to stay a bit active next week, it’s tough to say exactly what that means with any specificity.

Happening Now: Annoying Atlantic

We have Philippe, and we have Invest 91L that continue to churn in the Atlantic. Philippe has gotten virtually no stronger since yesterday. Invest 91L continues to have high odds of development, probably by tomorrow or Thursday.

Invest 91L is expected to essentially tail Philippe west, and while Philippe dissipates near the islands, 91L should be gathering some strength as it readies to curve northward. (Tomer Burg)

You can see from the map above how the track of Philippe is essentially trailed by the area of potential development from 91L, which is the red highlighted area. The intensity of each system will determine just how close it gets to the islands. The current thinking is that Philippe will dissipate north of the islands in the coming days. Invest 91L should take over as the better organized system, but even in the most extreme case, it would most likely pass north and east of the islands. Even if it did track farther south and west and closer to the islands, that would be due to a weaker system. So, it’s probably wise to keep watch on how this all plays out if you live in the northern Leeward Islands or Puerto Rico, but the vast majority of decent data seem to support a miss.

The medium range (days 6 to 10): Noisy near Florida

Early next week should be dominated mostly by what we see in the Atlantic. But as we get to the middle and end of next week, we have noise continuing to percolate in the modeling on either side of Florida. We’ve had some bizarre solutions printed out by modeling since the weekend, including systems backpedaling southwest from off the Carolinas to something in the eastern Gulf moving northeast across Florida and out to sea to some model solutions showing absolutely nothing whatsoever.

The forecast for the mid-levels of the atmosphere on the last 10 GFS model runs for next Thursday tell us absolutely nothing useful. (Tropical Tidbits)

I think that’s an important element of this. Usually when you have this kind of inconsistency and only tepid ensemble model support, you have enough justification to be skeptical that anything will occur. So while I think this is certainly a region to watch in the days ahead, the most likely outcome is probably that nothing of note happens. We’ll obviously continue to watch to see what evolves in the days ahead.

Fantasyland (beyond day 10): Noise but no signal

We’ve seen no change in modeling since yesterday with respect to the extended range period. There are signs of potentially something in the western Caribbean or southeast Gulf, but there’s no signal whatsoever to what is there. In other words, I see some ensemble members of the various models showing me signs of development, but I see no consistency and no real consensus yet.

Historical points of origin of tropical systems in the first third of October focus our attention on the Bay of Campeche and northwest Caribbean. (NOAA NHC)

Climatologically, that’s exactly where you would be looking in early October. So it’s not a surprise that that is what we’re doing. But until we see any kind of signal in this soup, there’s little we can say beyond “it’s worth watching.” Especially for the eastern Gulf or northwest Caribbean.

September 25, 2023 Outlook: Philippe and perhaps a friend will traverse the open Atlantic this week

One-sentence summary

Neither Tropical Storm Philippe or Invest 91L are expected to impact land at this time, but there are a couple other areas to keep tabs on beyond this week.

Happening Now: Philippe and 91L are not serious concerns

It’s the last full week of September, and in the Atlantic tropics we continue to pace ourselves with a couple storms per week. This week, we have Philippe, which formed over the weekend. We may add Invest 91L to the mix later this week, as it may have a window of opportunity to become Rina.

First, Philippe. While it has plenty of thunderstorm activity that it is maintaining this morning, it’s very clearly ragged looking, an indication that it is fighting off wind shear.

Tropical Storm Philippe is juiced up pretty good this morning, but it is clearly fighting off a good deal of wind shear. (Tropical Tidbits)

Philippe has 50 mph maximum sustained winds, but with the wind shear it is experiencing, it may struggle to intensify much beyond this over the next couple days. If Philippe can survive this stretch, there is some chance it may take a run at hurricane intensity by later in the week out over the open ocean, no threat to land. If Philippe succumbs to shear the next few days, it may actually stay on a westward course and get close to the islands. However, in that case, it would be unlikely to reintensify and impacts would be minor.

Tropical Storm Philippe is expected to hold its own over the next few days, eventually turning out to sea or falling apart northeast of the Lesser Antilles. (NOAA NHC)

So in terms of impacts in the Lesser Antilles, both a stronger Philippe and a weaker Philippe should make no difference. A stronger Philippe turns away faster and much farther east. A weaker Philippe tracks closer but falls apart.

Meanwhile, Invest 91L got tagged this weekend behind Philippe, and it is essentially following Philippe to the west. I’d expect a slow, gradual intensification this week and maybe an organized depression or storm by Wednesday or Thursday.

Invest 91L is expected to essentially follow Philippe to the west and north, though its ultimate outcome will be dictated by how strong it gets; stronger out to sea faster, weaker more south and westward but never organizing much. (Tomer Burg)

Ultimately, 91L’s future may be dictated (much like Philippe’s) by how strong it gets. A stronger storm would be apt to turn away from the islands quicker, whereas a weaker one would track closer but come with limited impacts. Either outcome produces minimal heartburn for the islands. We’ll keep track.

Finally, the NHC has highlighted an area in the far southeast Gulf with a 10 percent chance of development.

That seems reasonable right now. Wind shear is low for the moment, but it is expected to increase and expand over the Gulf this week, which should essentially shut down anything that tries to develop. So we are not worried about this one.

The medium-range (days 6 to 10): Eastern Gulf or East Coast shenanigans?

Could we do another Ophelia situation on the East Coast or even in the Gulf next week? The answer is maybe. Some modeling has hinted at a disturbance in the mid-levels of the atmosphere coming together somewhere around Florida, perhaps not far from where Ophelia developed last week. I think the ballet here is a little more delicate than it was last week, which would mean that we’d need a few more things to come together perfectly for this to happen. But if it were to do so, we could conceivably be talking about another tropical storm either in the Gulf or off the East Coast next week. Something for us to watch, but nothing I have enough confidence in today to say much more about. This is very much a stay tuned situation.

Fantasyland (beyond day 10): Still a bit noisy

I can’t hone in on anything specific right now, but in looking at all the modeling beyond day 10, I would think that we’re onto something, potentially in the western Caribbean. Again, I’m not certain that this will happen, but it’s the one place I’d be watching into mid-October. We’ll fill in the gaps on this as we get a little closer. It’s frustratingly vague to be sure, but that’s simply the reality of trying to forecast 10 to 15 days out.

September 23, 2023 Outlook: Ophelia inland and newly formed TD 17 expected to miss the islands

One-sentence summary

Tropical Storm Ophelia is inland and weakening, providing heavy rain from North Carolina into Virginia today, with local moderate to major tidal flooding possible again this evening in the Mid-Atlantic.

Tropical Storm Ophelia: 50 mph maximum winds, moving N 13 mph

Ophelia is now inland and weakening over North Carolina after making landfall earlier this morning near Emerald Isle, NC as a 70 mph tropical storm. The center is just north of Greenville as of this writing, moving due north at a steady clip. Heavy rain is falling across much of interior eastern North Carolina, as well as most of southeastern Virginia.

Ophelia is moving north in North Carolina, bringing heavy rain and flash flooding to parts of the area. (RadarScope)

There is a moderate risk of flash flooding (level 3 of 4) today for southern Virginia and northern North Carolina. Another 1 to 3 inches of rain is easily likely in spots. Those that see the heaviest rain will be most prone to localized flash flooding. Expect inconvenient travel across much of the region today.

A moderate risk (3/4) for flash flooding is posted for the Richmond area into northern North Carolina. (Pivotal Weather)

Tidal flooding remains a concern. The high tide cycle later this afternoon and evening will probably be the last serious one, but we still expect moderate to locally major tidal flooding between Hampton Roads and the Jersey Shore.

Widespread moderate and locally major tidal flooding will be a concern with the late afternoon or evening high tide cycles in the Chesapeake and Mid-Atlantic. (NOAA)

Heed the advice of local officials to ensure you’re prepared for any flooding of streets or vehicles that may occur on the coast.

Additionally, winds continue to blow with Ophelia moving inland. Though, truthfully, the most recent map of wind gusts 35 mph and higher is not exactly going to scare anyone.

A modest amount of 35 to 50 mph wind gusts (there’s a 49 not shown here on the coast of Delaware at an elevated site) are occurring, but nothing that should cause severe issues. (NOAA)

There are a modest amount of power outages, which right now sit at around 60,000 or so. All in all, not terrible. So the main concerns today will be around the rainfall flooding and the high tide cycle later today. Use caution and don’t drive into flooded roadways.

We’ll get more rain into tomorrow as you work up the coast, with 1 to 3 inches possible and a slight risk (level 2 of 4) of flash flooding from the Philly area up into southwest Connecticut, including much of New Jersey and New York City.

Otherwise, we’ll lose Ophelia tomorrow or Monday, and it will dissipate offshore. Some models do show its remnant “energy” hanging around offshore, but right now that seems like a non-serious concern. We’ll keep tabs on it regardless.

Tropical Depression 17: Deep Atlantic system unlikely to impact land

Within the last hour or so, the National Hurricane Center upgraded Invest 90L to Tropical Depression 17. This is the deep Atlantic system we’ve been watching for awhile now in modeling. The good news is that most trends have adjusted to turn this thing north before it gets near the islands. A “close miss” is not off the table, but this is looking more and more like a clear miss.

Tropical Depression 17 is expected to become Tropical Storm Philippe this weekend before turning northwest or north before arriving in the Caribbean islands. (NOAA NHC)

The system is expected to gradually strengthen over the next few days, becoming a tropical storm (named Philippe) later today or tomorrow and eventually a strong tropical storm. It could eventually become a hurricane, but that’s not currently forecast officially. Whatever the case, at present this is no threat to land.

Beyond these two systems, there is not anything of serious concern at this point in the basin. Hopefully we are now past the peak of hurricane season and we’ll see if the secondary, lower October peak brings us anything of note.