ATL: LEE - Post-Tropical - Discussion

[dexterlabio]

So this could turn out to be either an Irma or a Maria 2.0? Hope it won't be the case but the activity in this basin so far has been astounding it's reminiscent of 2017.

[cycloneye]

Eastern and Central Tropical Atlantic (AL95):
A tropical wave located over the far eastern tropical Atlantic is
producing disorganized shower and thunderstorm activity to the
south of the Cabo Verde Islands. Environmental conditions appear
conducive for some gradual development of this system by the middle
part of next week, and a tropical depression is likely to form while
it moves westward to west-northwestward at 15 to 20 mph over the
eastern and central portions of the tropical Atlantic.
* Formation chance through 48 hours...low...20 percent.
* Formation chance through 7 days...high...70 percent.

[Cachondo23]

The GFS has a notorious bias for making the background environment look unfavorable, and thats simply not true, the environment is primed for this thing to take off, now its a question if this thing goes south of the islands or north, any land interaction will be key

So not a little bit of dry air and shear on its way like their saying?

[Blown Away]

Eastern and Central Tropical Atlantic (AL95):
A tropical wave located over the far eastern tropical Atlantic is
producing disorganized shower and thunderstorm activity to the
south of the Cabo Verde Islands. Environmental conditions appear
conducive for some gradual development of this system by the middle
part of next week, and a tropical depression is likely to form while
it moves westward to west-northwestward at 15 to 20 mph over the
eastern and central portions of the tropical Atlantic.
* Formation chance through 48 hours...low...20 percent.
* Formation chance through 7 days...high...70 percent.

20 mph, not always, but IMO most of the time AOI’s have trouble getting real strong/deep while moving that quickly.

[Sciencerocks]

[cycloneye]

Looking at visible, we have this healthy wave pouch with a distinct AEW troughing pattern (purple) along with our wave axis (green):
https://i.imgur.com/0Xb1D3L.png

This creates an offset mid-level circulation (MLC), that's vaguely outlined here (orange):
https://i.imgur.com/9BJ1lfv.png

What occurs is we have two points of interest along the eastern flank of the pouch, where vorticity is favored on the northern and southern wave axis (highlighted in red):
https://i.imgur.com/9rhP3A9.png

While a LLC can develop anywhere within the AEW pouch domain, broadly outlined in blue, both vorticity lobes will typical continue to pivot around the mid-level circulation:
https://i.imgur.com/IUXBRNa.png

We can see this is the general setup analyzed on the 12z GFS:
https://i.imgur.com/TNMAl7n.png

As far as the short-term forecast, models have backed off on development for two distinct reasons. In the first 72 hours, both the GFS and ECMWF forecast unidirectional shear. This is where we have weak steering currents from the low levels up to the mid level of the atmosphere (highlighted in red). Meanwhile, wind speed is increasing with heights in a consistent direction (pink). This creates a tilted structure that we can see on visible, with a displacement of the mid-level circulation to the west of the wave axis (this is why the western flank of the AEW is convectively active).
https://i.imgur.com/euCvlY0.png

While shear relaxes thereafter, consistent vort training of the northern lobe has the moisture envelope associated with 95L more to the north with each run. In addition, models have trended towards a stronger Katia (and trended more south). This creates increased flow directly to the north of 95L, and this begins to strip some of the moisture envelope away:
https://i.imgur.com/gt0RLgy.gif
https://i.imgur.com/QwR5Rg0.png

USTropics, to let you know that moved your great post from the models thread to here.

[cycloneye]

18z Best Track more low in latitud, from 9.9n at 12z to now 9.5n.

AL, 95, 2023090218, , BEST, 0, 95N, 203W, 25, 1010, DB

[Stratton23]

Chachondo23 their may be some shear and dry air, but its still a favorable environment, and the GFS has a biacy to overdue both sometimes, hence its a model that cannot be trusted right now given how its shown no consistency at all every run with this system

[MarioProtVI]

Chachondo23 their may be some shear and dry air, but its still a favorable environment, and the GFS has a biacy to overdue both sometimes, hence its a model that cannot be trusted right now given how its shown no consistency at all every run with this system

The Euro also keeps it weak in the MDR. I think the models realized it’s El Niño (even though it hasn’t been acting like that) and adjusted so. A Cat 5 is pretty much out of the question, and perhaps a Cat 4 is unlikely as well.

[Blown Away]

18z Best Track more low in latitud, from 9.9n at 12z to now 9.5n.

AL, 95, 2023090218, , BEST, 0, 95N, 203W, 25, 1010, DB

Yeah, most of the TW’s have been coming off Africa @15N and those will almost always go OTS.

[cycloneye]

They ajusted the whole best track file and since 12z of Friday, it hass been at latitud 9.5n.

[GCANE]

Latest GFS 355K PV looks conducive for development all the way to the GoM

[Teban54]

Chachondo23 their may be some shear and dry air, but its still a favorable environment, and the GFS has a biacy to overdue both sometimes, hence its a model that cannot be trusted right now given how its shown no consistency at all every run with this system

The Euro also keeps it weak in the MDR. I think the models realized it’s El Niño (even though it hasn’t been acting like that) and adjusted so. A Cat 5 is pretty much out of the question, and perhaps a Cat 4 is unlikely as well.

Sorry, but I think this is a really bad take.

[GCANE]

Currently GFS is forecasting a strong Rossby Wave trofed over MI with an associated surface low when the TC gets in the west Carib.
Need to pay attention to timing which influences the turn north.

[IcyTundra]

Chachondo23 their may be some shear and dry air, but its still a favorable environment, and the GFS has a biacy to overdue both sometimes, hence its a model that cannot be trusted right now given how its shown no consistency at all every run with this system

The Euro also keeps it weak in the MDR. I think the models realized it’s El Niño (even though it hasn’t been acting like that) and adjusted so. A Cat 5 is pretty much out of the question, and perhaps a Cat 4 is unlikely as well.

Don't hug the models.

[zzzh]

Chachondo23 their may be some shear and dry air, but its still a favorable environment, and the GFS has a biacy to overdue both sometimes, hence its a model that cannot be trusted right now given how its shown no consistency at all every run with this system

The Euro also keeps it weak in the MDR. I think the models realized it’s El Niño (even though it hasn’t been acting like that) and adjusted so. A Cat 5 is pretty much out of the question, and perhaps a Cat 4 is unlikely as well.

El Nino brings easterly shear to the system?

[zzzh]

They ajusted the whole best track file and since 12z of Friday, it hass been at latitud 9.5n.

https://i.imgur.com/fCS3yCj.jpg

Very unreasonable. ASCAT clearly showed that the center was at 10N.

[Category5Kaiju]

Chachondo23 their may be some shear and dry air, but its still a favorable environment, and the GFS has a biacy to overdue both sometimes, hence its a model that cannot be trusted right now given how its shown no consistency at all every run with this system

The Euro also keeps it weak in the MDR. I think the models realized it’s El Niño (even though it hasn’t been acting like that) and adjusted so. A Cat 5 is pretty much out of the question, and perhaps a Cat 4 is unlikely as well.

Ok, I'm going to have to strongly disagree with you there, especially with your speculation that this basically has very little chance of attaining Category 4 status as well.

Now I'm not trying to point any particular individual out here, but it seems like with models delaying development closer to the islands there's been a bit of a general overreaction in the wx community that that basically means El Nino is kicking into gear and that 95L is going to underperform. If we look at how the EPAC is behaving, how the Atlantic has behaved recently, and how the Atlantic shear isn't westerly but rather easterly, I think it's a bit crass to conclude that all of a sudden this all means El Nino came and will make TC formation hard in the Atlantic.

[abajan]

Chachondo23 their may be some shear and dry air, but its still a favorable environment, and the GFS has a biacy to overdue both sometimes, hence its a model that cannot be trusted right now given how its shown no consistency at all every run with this system

The Euro also keeps it weak in the MDR. I think the models realized it’s El Niño (even though it hasn’t been acting like that) and adjusted so. A Cat 5 is pretty much out of the question, and perhaps a Cat 4 is unlikely as well.

Don't hug the models.

While it's unwise to hug any particular model, it appears something's up when several of them simultaneously back off on development.

[WalterWhite]

Is this thing classifiable? I think there is already a closed low based on the last ASCAT pass.