Matt Lanza

September 29, 2023 Outlook: Atlantic ballet and non-tropical flooding risk in NYC metro

In case you missed it yesterday, we had our first real non-tropical post in which we discussed the ongoing salt water intrusion issues in Louisiana related to low-flow of the Mississippi River. While today’s post functions as an outlook, we will also discuss the developing flooding situation for New York City.

One-sentence summary

Philippe and Rina will dance, with Philippe eventually taking over as the dominant system, lifting into the Atlantic, while today we also check in on flooding in New York City.

Tropical Outlook: Philippe & Rina dance, while the rest of the basin settles down

Philippe & Rina

These two. Tropical Storms Philippe and Rina are now unable to be dissociated from one another, as we are seeing the Fujiwhara effect play out in real time. The two storms will interact and probably repel one another, with Rina likely taking a backseat to Philippe.

Philippe and Rina will track near each other with Philippe most likely to become the dominant system in the Atlantic before turning north. (Tomer Burg)

Basically, Philippe will stall, Rina will sling shot over the north side of Philippe, turn north and dissipate, and then Philippe will begin moving out to sea again. There has been a good deal of model uncertainty, particularly with respect to Philippe’s future intensity. And that is normal for a Fujiwhara interaction. When two storms engage like this and are this close together, inherent uncertainty increases, and that leads to a bit of forecast uncertainty. It’s becoming more likely however that Philippe becomes a stronger storm that pulls north, and I wouldn’t be to see the National Hurricane Center bump up their forecast intensity as it moves north into the open Atlantic.

Philippe and Rina will dance around each other over the next 4 or 5 days before Rina likely dissipates and Philippe becomes a larger storm over the open Atlantic. (Weathernerds.org)

As we’ve noted through the week however, even in the unlikely event that one of these systems ends up in the islands, it will be on the lower end of intensity and unlikely to create too much trouble. But confidence seems to be building in a no-impacts scenario. Both of these systems should be on their way out by later next week.

What else is out there?

Throughout the week we’ve also told you a bit about potential upper low or weak tropical development off the Southeast coast next week. Support for that has faded as a pretty decisive autumn cold front sweeps across the Southern and Eastern U.S. later next week. Finally! The hope would be that this leads to quieter tropics for a time. The season is by no means over (though for the northwest Gulf and Cabo Verde region it probably is), not with record warm water temperatures out there, but the pace should finally slow a bit. We’ll have more on this next week.

Metro New York City flooding underway

A few flash flood warnings have already been posted for the New York City area this morning as heavy rains stream into the area. Most of the City outside of the Bronx has seen some flooding with 1 to 3 inches of rain so far and the potential for a good deal more to come.

Heavy rain will continue to push into New York City and Long Island today, setting up a fairly substantial flash flooding event in that area. Travel to NYC area airports will likely be impacted through afternoon (RadarScope)

This should continue the flash flooding threat across northeastern New Jersey, New York City, Long Island, and southwest Connecticut. It’s likely that the heaviest rain will fall somewhere between Islip on Long Island and Newark, NJ. The worst conditions will be this morning into early afternoon with gradual improvement this evening.

The Weather Prediction Center arm of the NWS has set a moderate risk (level 3 of 4) for excessive rainfall and flooding in the Tri-State area around NYC. (Pivotal Weather)

Some places could see in excess of 3 or 4 inches more rainfall which will likely lead to considerable street and some local creek or river flooding. Be safe in the New York City area today, and if you’re traveling that direction, be prepared for some delays and hassle.

To solve Louisiana’s Mississippi River salt water crisis a significant weather pattern change is needed. Is any in sight?

At The Eyewall, we’ve focused on hurricanes and tropical storms since our launch in June. Some of you have asked what we’ll do during the offseason, and the answer is we will probably pull back our posts to every few days unless there’s a major weather event, and we will focus on extreme weather impacts in North America. We don’t want to offer clickbait or drama, but a forecast, an explanation, and context. I’ve decided to roll out something of that nature today with a focus on the Mississippi River salt water intrusion crisis in Louisiana.

One-sentence summary

The situation with salt water creeping up the Mississippi River in Louisiana is a complex one but one that has a basic solution (more rainfall) that does not look likely to be in the cards over the next 2 to 3 weeks in any meaningful capacity.

What is happening?

If you’ve been following the news lately, you may have heard about salt water creeping upriver in the Mississippi River in Louisiana. In the most simple terms, as dry weather has led to low river flows in much of the Mississippi Valley, denser salt water has been able to creep north at the bottom of the river. This isn’t unprecedented, but it isn’t common either. This happened to a much lesser extent last year and more notably back in 1988, when the salt water barrier shifted over 100 miles up the river west of New Orleans. This led to a couple days of salt water intrusion into New Orleans’ water supply which ended quickly.

WWNO, the NPR affiliate in New Orleans has a great rundown of what’s happening.

Tulane’s School of Public Health & Tropical Medicine also published a “5 things to know” that is helpful.

Virtually the entire Mississippi Valley is in drought right now, with a good chunk of the Missouri and Ohio River Valleys that feed the Lower Mississippi also in drought or abnormal dryness. The hot, dry summer in Louisiana in particular has exacerbated the dryness and drought there, with the entire southern two-thirds of the state in either exceptional or extreme drought.

Louisiana is in pretty terrible drought right now, but the situation upstream on the Mississippi is only marginally better, with widespread dry or drought conditions into Minnesota and along the Missouri and Ohio Rivers as well. (US Drought Monitor)

The last 60 days have seen 5 to 50 percent of normal rainfall along the Mississippi south of Memphis. The Ohio Valley and Missouri Valley have both seen 50 to 75 percent of normal rain. All this combined with the extreme drought in Louisiana has led to a confluence of problems and an expanding salt water wedge.

Over the last two months, rainfall has been 25 percent of normal or less in much of southwest Mississippi and Louisiana, and only marginally better than that in most areas along the Mississippi, Ohio, and Missouri Rivers. (NOAA)

What is the rainfall outlook?

To solve this problem, the main thing you need is just simply rain. It needs to rain in the Ohio, Missouri, and Mississippi Valleys sooner than later. Is there anything in sight over the next two weeks? Not really. The Lower Mississippi Valley should see minimal relief. The Ohio Valley looks quite dry. The Missouri Valley and Upper Mississippi are more mixed, but we’re just not seeing signs of any appreciable rainfall over the next two weeks.

Both the European model (shown here) and the GFS model are advertising below average precipitation over the next two weeks over virtually the entire Mississippi River drainage basin. (Weather Bell)

This is why you are seeing so much news about preparations for this in New Orleans and other Louisiana communities. Without meaningful rain over the next two weeks, you will continue to see the salt water migrate north. Current weather forecasts push us out to about mid-October and current projections for the wedge have it getting to New Orleans in later October. Even if 10 inches of rain fell over Memphis on October 15th, it would take some time for that water to flow downstream and get to New Orleans and southeast Louisiana. And isolated rain is not the answer. This problem requires a lot of upstream rain over a broad area. So it seems pretty clear that this problem is going to worsen.

So when can we expect a change? Well, when we look at the Climate Prediction Center’s outlook for weeks 3 and 4 (and granted, this is from last Friday), we can see signs of life in Texas or the Southern Plains, but probably nothing that would help “solve” the problems in Louisiana.

The situation within the Mississippi Basin does not look to improve a whole heck of a lot in mid October either. (NOAA)

The CPC outlook for October is positive with a lean toward above normal rainfall in the mid-Mississippi Valley. I’m not sure if changes over the last week since this map’s release have necessarily lowered chances of this outcome, but I don’t believe they’ve helped much.

The bottom line: The situation with salt water in the Mississippi River is going to worsen in the coming weeks, and there is not necessarily any strong signal for changes in the rain patterns over the key areas required to alleviate the problem. We need to see a change in the rainfall chances in either or all of the Ohio, Mississippi, and Missouri River Valleys before we can be confident that some help will be on the way. And at least into mid-October and possibly late October, that’s not likely to occur.

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.