Matt Lanza

Lemony: A series of unfortunate Atlantic disturbances

Headlines

  • There are multiple areas to watch in the Atlantic, none of which is really a major concern in terms of development.
  • The main place to watch is the Gulf of Mexico, where heavy rain in Louisiana today from a frontal low is causing localized flooding.
  • The Caribbean wave may make a slight effort to develop next week in the western Gulf, but again, the primary concern will be rainfall in coastal Texas and Louisiana as that moisture lifts north and northeast.
  • A return to more “average” basin conditions may unfold late in the month.
Lemons all over the NHC outlook map today, but none of these areas is of serious concern at this time. (National Hurricane Center)

If you asked me in May to tell you what the NHC outlook map would look like on September 5th, I would have said that it would look something like the map above, though perhaps with more orange and red shaded regions and/or named storms. But, busy. If you asked me how many of those areas on that day would be of actual concern, I would have guessed about four. Instead, we got the map, but of the 5 outlined areas, maybe 0.5 is of actual concern — and not even really because it has a chance to develop.

The three Atlantic disturbances are honestly of no consequence. The one northwest of Bermuda (Invest 99L) is likely to track toward Atlantic Canada as a rain maker and gale heading toward the weekend. We’re looking at 20 to 60 mm of rainfall for Nova Scotia, PEI, and portions of eastern New Brunswick from this in addition to rough marine conditions.

Invest 99L will produce some rough marine conditions and locally heavy rain as it moves into Atlantic Canada this weekend. (Pivotal Weather)

The other two disturbances in the Atlantic are likely to stay out at sea and end up on the lower-end of the intensity scale as it stands right now.

Caribbean wave & Gulf of Mexico permalow: Mainly a rain concern

Flash flooding is ongoing in parts of Louisiana as heavy rain associated with a frontal low in the Gulf of Mexico expands north and east today.

Because this low tried to consolidate a bit this morning, the heaviest rain has occurred well offshore with close to 15 inches estimated in some cases.

Estimated rain totals of 1 to 3 inches on the coast of Louisiana and Texas have occurred in the last 24 hours, with heavier rain offshore and farther east around Lake Pontchartrain, where 2 to 7 Inches or more has fallen. (NOAA MRMS)

However, very heavy rain has occurred and is continuing in parts of eastern Louisiana and even southern Mississippi where upwards of 5 to 7 inches has occurred in spots, heaviest between I-10 and I-12 near Lake Pontchartrain and just east of New Orleans into Hancock County, Mississippi. This low will be sheared apart, with one piece heading eastward and another southward over the next 48 hours. The first Gulf Coast cold front of the season arrives in places like Houston and Lake Charles into Mississippi and Alabama this weekend. That will help clear the deck.

So then what? Well, this tropical wave that we’ve been discussing for days now finally makes it into the Bay of Campeche this weekend. It will sit and fester a bit, sort of merging together with the piece of the current system in the Gulf that will also fester down there. And you get another low pressure system. The Gulf is home to a permalow this month. Modeling goes two ways with this. The generally trustworthy European ensembles limit development risk of this area to maybe 40% for a depression and 30% or less for a tropical storm.

Probability of a tropical depression based on the European ensembles is around 40 percent or so (this tends to get overdone a bit) and odds of a tropical storm are 30 percent or less in the Gulf. (Weather Bell)

The storm track would probably be north and northeast toward Louisiana, and the ceiling on this would be low, probably below strong tropical storm intensity. However, more volatile models like the European AIFS (AI model) and ICON (German model) show this developing into a tropical storm, tracking toward Louisiana as well next Wednesday. In the former case, with no real development, we end up with a situation like we saw this week: Heavy rain at times near the coast midweek next week. But no organization. In the latter case with development, we get a coherent tropical storm and heavy rain offshore that crashes into Louisiana next week.

The bottom line: The primary concern next week will continue to be excessive rainfall. Secondary will be tropical development which does not appear to be a serious concern at this time.

GFS model forecast rainfall for next Wednesday and Thursday showing pockets of isolated heavy rain again on the Texas coast, but little to no tropical development. (Pivotal Weather)

The map above is the GFS model forecast for Wednesday and Thursday next week which shows isolated heavy rain on the Texas coast and near Louisiana, very similar to what we’ve seen this week. Even if no tropical development occurs, a localized flooding concern may emerge again next week on the Gulf Coast of Texas or Louisiana.

Beyond all this, there’s not much else doing out there that’s of concern. There are hints that the widespread sinking air in the background of the Atlantic basin may relax a bit in the final third of the month, but we also saw that possibly happening a few weeks ago and it didn’t. So while I would suspect things could turn more active toward October, I also want to be cognizant of the fact that this a forecast we’ve made before that hasn’t panned out. So for now, we’ll call for a gradual return to more normal activity in the Atlantic heading toward October, which is to say not as active as feared this season but more active than it is presently.

Atlantic still sputtering along with few development concerns over the next 2 weeks

Headlines

  • Texas has seen extremely heavy rain with more to come, including in Louisiana through Friday.
  • A Caribbean tropical wave still merits watching, though any real serious risks are quite low, though it will bring heavy rain to Mexico.
  • The rest of the Atlantic looks quiet for the foreseeable future with a background of suppressed air likely keeping a lid on any disturbances.

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Unnamed storm system pounding Texas with heavy rain

While the Atlantic is net quiet overall, there remains the one area to monitor in the Caribbean and eventually Gulf. In fact, the whole western Gulf is a mess still with a stalled front and surface low pressure continuing to produce widespread showers and pockets of heavier rain. Some locations just north of Corpus Christi saw upwards of 8 to 9 inches of rain this morning, and heavy rain continues in some spots there.

48 hour rainfall totals have been as high as 8 to 9 inches near Aransas Pass and 3 to 7 inches over a wide area of the Texas coast. Couple this with the significant rain seen last week on the upper Texas coast and you have a major rainfall event that’s unfolded. (NOAA MRMS)

The problem is that with steering currents basically collapsed here, everything has moved slowly. As I write this, there’s a band of heavy rain aimed at Aransas and Calhoun Counties that has produced roughly 2 inches of rain in an hour. These bands get stuck and hit one location like this for 2 to 4 hours, leading to 4 to 8 inches of rain and flash flooding.

On top of this, we have had a persistent pattern with a stalled front in interior Texas that has led to massive rain totals of 2 to 8 inches or more across Hill Country, a place that will happily take most of this rain as prolonged drought has hammered this beautiful part of Texas. The stagnant pattern is going to begin unclogging over the next 36 hours, but not before another round of heavy rain likely impacts Louisiana and the upper Texas coast.

While interior Texas rains taper off, one more round of heavy rain is likely between Matagorda Bay and Louisiana, where 4 to 8 inches of new rainfall and flash flooding will be possible. (Pivotal Weather)

After another 4 to 8 inches is likely along the upper Texas coast and into Louisiana, this “no-named” system will probably leave some places with just shy of 15 to 20 inches of rain since last week when all is said and done.

Caribbean tropical wave remains a stubborn low risk

A cold front will sweep all this away from Texas and Louisiana over the weekend. By then, the Caribbean tropical wave we’ve been watching since last week should be over the Yucatan or Central America. Development odds remain about 30 percent this morning, and looking at satellite, it remains a poorly organized mass of disjointed thunderstorms south and southwest of Hispaniola today.

Showers and thunderstorms south of Jamaica and Hispaniola remain associated with a very disorganized tropical wave in the Caribbean. (Weathernerds.org)

As this wave moves westward, any development will be sluggish before it comes ashore in Belize or the Yucatan. From here, it remains uncertain how things will play out, but any sort of re-emergence into the Bay of Campeche would bear some watching. That said, is that the likeliest outcome? Not necessarily. Of the 51 European ensemble members, about 20 percent push this into the Bay with some development. Of the 51 members, about 5-10% maybe bring it north into the Gulf. Never tell me the odds, but I like those odds right now.

The European ensemble model is not exactly eager to bring this tropical wave back into the Bay of Campeche, but it still merits watching. (Tropical Tidbits)

So, yes, we should continue to monitor the progress of things here of course! But as of right now, other than the ICON model, which is quite aggressive in developing this, and the European AI model, which brings it north and northeast into the central Gulf as what appears to be a subtropical storm, there is no significant model support from our traditionally best performing models for this to become a huge deal.

That said, we are looking at anywhere from about 5 to 15 inches (over 300 mm) of rainfall for portions of Mexico from this, so flooding could become an issue there.

Rest of the Atlantic is unimpressive

We continue to look for signs of life in the deep Atlantic, and while there remain two waves of note, neither appears to be a meaningful concern to anyone really.

A couple tropical waves in the deep Atlantic merit light watching, but there are no concerns for land masses at this point from either of these. (Weathernerds.org)

The two tropical waves in the open Atlantic have about a 10 and 20 percent chance west to east respectively of developing. The lead wave may bring some showers and storms to the islands, while the trailing wave is likely destined to go out to sea. There’s nothing emerging off Africa right now, and then next wave is a few days away. That wave may have a decent chance to develop I guess, but it too looks to remain out at sea right now.

Again, there’s just nothing inspiring in the Atlantic. And I’m not sure we’re going to see much either. If we look at what’s happening in the background of the Atlantic, we have broad sinking air dominating the western two-thirds of the basin, much as it has since early August. Any rising air has shifted from the Indian Ocean more toward Oceania and Indonesia. Sinking air tends to suppress storm development, while rising air tends to help storm development along. So, this doesn’t support robust disturbances in the western Atlantic. This strongly argues that we’re going to see muted activity continue through mid-month. Again, this is one of those intraseasonal signals we cannot predict in April or May that can have an outsized impact if they setup correctly. And in this case, they have certainly done so.

A complex Hovmoller plot which shows generally sinking air (red/orange) dominating in the area corresponding to the western 2/3 of the Atlantic basin. (StormVista)

Even a couple weeks ago, this signal seemed to indicate it would become less hostile to tropical development by early to mid-September. That’s now getting kicked down the road. Unless you chase hurricanes for a living, it’s hard not to be thrilled by this situation sitting here on September 4th. We’ll keep an eye on things.

Caribbean wave struggling but worthy of monitoring, while the surprisingly muted Atlantic plods forward

Headlines

  • A tropical wave in the Caribbean maintains about a 30 percent chance to develop in the coming days.
  • Model guidance doesn’t quite eliminate that wave as a potential area to monitor for the Bay of Campeche and/or Gulf, but very few models are bullish on intensity right now.
  • The rest of the Atlantic is rather quiet for September.
  • A potentially historic rain event in the Sahel and Sahara Desert may be symptomatic of bigger issues at play that could partially explain some of this season’s failure to launch.

Caribbean wave continues to lurk

The number of forecast consensus iterations on this Caribbean tropical wave over the last week or so have been rather annoying. Initially, we were discussing a system possibly heading out to sea. Then we started to discuss development farther west in the Caribbean followed by either a turn north or a continued track west. Then, even yesterday it looked like this was doomed to fail completely. And now today we have a new possible forecast wrinkle. In some ways, that’s “chasing” models, a practice that is not enjoyable, nor especially recommended. In other ways, I’m not sure what else you’re supposed to do with a struggling tropical wave that refuses to organize. It’s “guidance” for a reason, and in this case, the guidance has been shifting about.

Anyway, end rant. here’s the Caribbean wave on satellite this afternoon.

A tropical wave in the central Caribbean is producing widespread thunderstorms across Hispaniola and points south and east of Jamaica. (Weathernerds.org)

I mean, that’s a respectable amount of thunderstorm activity. But there’s no organization to things here. At least not yet. That could change in the coming days but probably not before Friday. Admittedly, this system is a bit confounding in that it’s generally in a healthy environment to organize but thus far it is not doing so. It could be sinking air in the background suppressing things, it could the 20 to 25 mph forward speed of the system, or it could be proximity to Hispaniola that is currently holding it back. As this reaches the western Caribbean, it may have a slightly better opportunity to organize, albeit slowly. Expect this to be positioned off the east coast of the Yucatan or near Belize by Thursday night.

From there, we will embark on a choose your own adventure scenario with this. A trough over the Eastern U.S. will attempt to pull this system north — if the system can gain enough strength to do so. That seems unlikely at this time. Steering currents will sort of collapse as that trough pulls away, leaving the system in the Bay of Campeche or nearby just sort of wandering aimlessly.

An animation of the mid-levels of the atmosphere between day 5 (Sunday) and day 10 (Thursday) shows the ensemble mean with a signal for the tropical system in the Bay of Campeche, but a complete break-down in confidence on placement late. (Tropical Tidbits)

You can see that above with last night’s European ensemble modeling. The mean of the 51 ensemble members shows a good signal for some sort of disturbance in the Bay of Campeche by Sunday but then a gradual dissolution of the signal by next Thursday. This suggests that the system will meander in or around the Bay of Campeche, maybe even onshore in Mexico next week. From there, as the steering currents collapse, we could see some northward drift to the system, particularly if it begins to organize. So no one should be entirely ruling this out. But at this point, there are mostly a bunch of hypotheticals and no clear signal on potential track or impacts, except to say that most guidance is generally lower-end with this one, the exception being the ICON model and some AI modeling.

In fact, as of the latest NHC tropical weather outlook, development odds with this have dropped to 30 percent.

A trio of tawdry tropical waves across the Atlantic. (NOAA NHC)

The Atlantic remains calm, mostly

There are two other areas noted on the NHC outlook above. Neither one should impact land over the coming days. The trailing wave closest to Africa may have the better chance to develop, though admittedly the leading wave looks a little healthier at the moment.

Bless the rains (up?) in Africa

But there are weird things happening right now, and we’ll certainly get into them in the days ahead. For one, tropical waves may again emerge too far north off Africa to really produce much in the way of development. In fact, if you look at the forecast rainfall as a percent of normal in Africa over the next 2 weeks, it very clearly shows that portions of the Sahel and even the Sahara Desert are expected to get more than their fair share of rainfall.

Rainfall over the next 2 weeks looks to be on the order of 750 percent of normal in northwest Africa, a truly extraordinary rain event in one of Earth’s driest locations. (StormVista)

This is truly odd. And possibly historic. Now, the amount of rain that can produce 500 to 750 percent of normal rainfall in those areas is probably a lot less than you’d expect. When your average precipitation totals are miniscule, well it doesn’t take much. But still, it’s impressive. There was a decent write-up about this from a site over in Europe that I think touches on some of what’s happening here, key among it: The inter-tropical convergence zone (ITCZ) is displaced just enough farther north than normal to have a strong impact on what we see in the Atlantic. Everything is connected in some way, and it’s plausible that such an outlier event is in some way related to the extreme, historic warmth of the Atlantic Ocean right now. I don’t want to overshoot my skis here, as this is not a topic I’m overly familiar with. But it will merit research and further analysis.

Some of the seeds of that research have been done already, with a recent paper led by author Dr. Kelly Nuñez Ocasio from Texas A&M. Their work suggests that more moisture in the atmosphere as both the oceans and atmosphere warm with climate change can lead to a shift in tropical wave coupling with thunderstorms. In other words, you would get something like we see now, with more waves and storms to the north, and less robust waves emerging off Africa in the places we expect to see them in September. It’s a fascinating study, and given that the paper was published in June, it could not be more timely.

Is this what we’re seeing? Maybe. There’s a theory that supports it, but you obviously can’t prove anything based on one event in one season. But given that we’re probably about to hear a whole lot of people screaming “bust” at the top of their lungs with respect to this hurricane season, it makes for a provocative possible explanation, among other things we’ve touched on.

Tropical wave bound for the Caribbean in no hurry to put itself together

Headlines

  • Model support for tropical development in the Caribbean has fallen off a bit since yesterday, but the wave that moves through there next week does still bear watching.
  • Low pressure in the Gulf of Mexico continues to serve up locally heavy rain on the Texas coast, where totals are approaching 10 inches or more.
  • Additional rain or localized flooding is likely through the week, shifting south a bit toward Corpus Christi as the week progresses. Tropical development, if any, would be slow and still on the lower end of intensity.

The little Caribbean wave that may or may not

Something funny has happened with hurricane season this year. Storms early on tended to outperform model expectations. Systems since mid-August that have shown in modeling are tending to look more lackluster longer. And indeed, the tropical wave we’ve been discussing that will pass through the Caribbean this week is following that pattern. Yesterday, the National Hurricane Center boosted development odds to 50 percent, only to back it down later to 40 percent. We’re still there today, but model trends in the last 24 hours have pulled back even more.

Tropical development probabilities are hovering around 40 percent with the tropical wave that will emerge in the Caribbean this week, and that may even be a bit generous. (NOAA NHC)

On satellite, this tropical wave remains nothing impressive. Yes, it has thunderstorms with it, and there will definitely be some heavy rain moving into the Lesser Antilles early this week, but any development is non-existent at this point.

The tropical wave just east of the Lesser Antilles remains poorly organized this afternoon. (Weathernerds.org)

And, look, that’s what we expected. We’ve been saying most of the last week that this was not going to be quick to develop, and so far that seems to be playing out. Yesterday we noted the inflection point that this system would hit in the western Caribbean when the atmosphere got a little less hostile to tropical development. We also noted that there was a distinct split in the European model ensembles with a bunch staying weak and going west toward Mexico or Central America and some that strengthened and turned northward. Indeed that continues today, but if the split was 60/40 yesterday, it’s 80/20 or even 90/10 today!

European ensemble members strongly support a weaker, more south and west track of the Caribbean wave after next weekend. There are a still a handful of stronger, farther north outcomes, but trends in the last 24 hours have been to back down on those. (StormVista)

The first thing many of you will say is “Oh, you said Beryl was supposed to do that too and look what happened!” That’s an understandable reaction. The difference this time around is 1.) this system is in no hurry to develop whereas Beryl was a Category 5 hurricane in the Caribbean, 2.) there is no real model support from models like the ICON or AIFS (AI version of the Euro) or even the GFS, and 3.) We have a cold front sitting off the Gulf Coast as this one approaches the western Caribbean. So this is a fundamentally different setup than in Beryl. We are going to continue to keep tabs on this obviously, but the message since yesterday has been to back down somewhat on development odds. There’s just something hindering development in the Atlantic basin right now. I think we continue to see generally sinking air in the western Atlantic in the background and overall more stability in the atmosphere than had been expected this season. This may now continue into mid-September.

Texas coast tallying nearly double digit rains

We’ve seen an additional 3 to 5 inches of rain since yesterday between Baytown, just east of Houston down to the Bolivar Peninsula and out to about High Island, bringing totals since Thursday up to about 6 to 12 inches of rain along the coast and just inland for portions of Texas. The highest officially measured total I’ve seen is 9.17″ at JB’s Seafood in Crystal Beach, where I believe Jefferson County has a gauge.

Radar estimates of rainfall since Thursday show 7 to 11 inches over a good portion of coastal Texas between the Bolivar Peninsula and Sabine Pass. (RadarScope)

Overall, models snuffed this one out well, though they were a bit overzealous inland. In the meantime, surface low pressure continues swirling today about 50 to 75 miles southeast of Galveston. It remains very disorganized.

A late morning surface analysis shows low pressure sitting off the Texas coast. It remains weak and disorganized. (NOAA WPC)

The low is expected to continue drifting offshore of Galveston for a few more days. It may eventually trend southward with time, closer to Corpus Christi. All the while there will remain a low chance it develops a little. But rapid intensification or strong organization is not expected with this system. Rainfall over the next 5 days looks to be on the order of 3 to 6 inches between Corpus Christi and Sabine Pass, with locally higher and lower amounts. A localized flash flooding risk remains very much in play for these areas.

Anywhere from 3 to 6 inches of additional rain is possible on the Texas coast between Corpus Christi and Sabine Pass over the next few days. (Pivotal Weather)

Thankfully, the rain has mostly been coming at a pace that is manageable. It’s just adding up in these locations over time. And that can lead to localized flooding eventually. For Houston, Beaumont, and Lake Charles, this is mostly a non-event with just passing showers or storms in the cards over the next several days. The stalled front in interior Texas may focus rainfall through the week in drier parts of the state.

Elsewhere, no tropical development of note is expected, and certainly no land impacts are expected over the next week.