ATL: INVEST 99L - Models

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TomballEd
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ATL: INVEST 99L - Models

#1 Postby TomballEd » Tue Aug 19, 2025 5:47 am

Euro ensembles not enthusiastic about 99L. The mandarin fishes and the lemon dies a lonely death in the MDR

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Re: ATL: INVEST 99L - Models

#2 Postby syfr » Tue Aug 19, 2025 7:35 am

TomballEd wrote:Euro ensembles not enthusiastic about 99L. The mandarin fishes and the lemon dies a lonely death in the MDR

https://i.imgur.com/pfR4mrM.png



We on the east coast, would call this good news.
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Re: ATL: INVEST 99L - Models

#3 Postby LarryWx » Tue Aug 19, 2025 12:10 pm

I’m not sure but am thinking this 12Z UKMET might be for 99L: E of Bermuda moving NNE at the end:

NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER 114 HOURS
FORECAST POSITION AT T+114 : 25.7N 64.2W

LEAD CENTRAL MAXIMUM WIND
VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS)
-------------- ---- -------- ------------- -------------
1200UTC 24.08.2025 120 26.9N 63.9W 1012 34
0000UTC 25.08.2025 132 29.9N 63.3W 1012 30
1200UTC 25.08.2025 144 32.0N 62.6W 1012 28
0000UTC 26.08.2025 156 34.8N 61.8W 1013 28
1200UTC 26.08.2025 168 37.5N 60.9W 1013 29
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Re: ATL: INVEST 99L - Models

#4 Postby TomballEd » Tue Aug 19, 2025 12:46 pm

Waiting to see what the 12Z Euro does, but 6Z is like 12Z, a system that forms and then dies. Through hour 144, some GFS ensembles develop 99L but all keep it weak. (A couple of the GFS ensembles seem to be hinting at that and getting a system into the Gulf)

Hard to say that if weak means it can avoid the weakness in the heights that got Erin and looks to get the mandarin. (Edited)


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Re: ATL: INVEST 99L - Models

#5 Postby USTropics » Tue Aug 19, 2025 1:01 pm

They are definitely two separate entities in the TWO, so I don't think they are anticipating a merger scenario. Invest 99L does look really good on satellite and vorticity products, the 12z GFS I would say even has a quick TC spinup here in the next 24 hours. In about ~2 days time though, the environment starts to get really rough. For starters, we get this trough that develops off the NW coast of Africa (CCW rotation in purple) and a ridge developing over the mid Atlantic (CW rotation in pink):

Image

This is going to drive dry air into the wave moisture envelope/pouch:
Image

In addition, that ridge in the mid Atlantic is going to really start to accelerate the mid-level flow to the west. Meanwhile, at the low levels the steering flow completely breaks down within the monsoonal trough:
Image

This is most clear in a sounding, where we can see the wind barbs near the surface (blue) is indicating even weak easterly flow, but our mid levels near 700mb and upwards (red) want to move westward. This is full on directional shear:
Image

So shear + dry air entrainment, there won't be much but a wave trough axis in 3+ days imo.
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Re: ATL: INVEST 99L - Models

#6 Postby LarryWx » Tue Aug 19, 2025 1:11 pm

I see nothing notable on the 12Z Euro regarding 99L. I don’t see any TC through at least 240 hours.
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Re: ATL: INVEST 99L - Models

#7 Postby Stratton23 » Tue Aug 19, 2025 1:24 pm

both the GFS/ CMC have this wave reaching the western caribbean in 10 days, worth keeping an eye on it
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Re: ATL: INVEST 99L - Models

#8 Postby SpaceCowboy » Tue Aug 19, 2025 3:58 pm

Stratton23 wrote:both the GFS/ CMC have this wave reaching the western caribbean in 10 days, worth keeping an eye on it


Is there any models of this yet?
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Re: ATL: INVEST 99L - Models

#9 Postby TomballEd » Tue Aug 19, 2025 4:11 pm

SpaceCowboy wrote:
Stratton23 wrote:both the GFS/ CMC have this wave reaching the western caribbean in 10 days, worth keeping an eye on it


Is there any models of this yet?



3 of 20 Canadian ensembles carry a TC into the Gulf after Day 10. Mexico and S Texas landfalls.
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Re: ATL: INVEST 99L - Models

#10 Postby Stratton23 » Tue Aug 19, 2025 4:15 pm

TomballEd yeah its pretty low, but definitely not zero either, we will see what 99L tries to do
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Re: ATL: INVEST 99L - Models

#11 Postby Hurricaneman » Tue Aug 19, 2025 4:40 pm

Stratton23 wrote:both the GFS/ CMC have this wave reaching the western caribbean in 10 days, worth keeping an eye on it

Not sure if it’s this one or the southern end of the 10/60 wave
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Re: ATL: INVEST 99L - Models

#12 Postby Stratton23 » Tue Aug 19, 2025 5:23 pm

Hurricaneman should be from 99L, if you look at the 12z GFS follow 99L’s energy at the 850 MB level, its weak but it passes by barbados and into the southern caribbean just north of SA, as it gets closer to the western caribbean, thats when things start to perk up a bit
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Re: ATL: INVEST 99L - Models

#13 Postby LAF92 » Tue Aug 19, 2025 8:10 pm

The 18z Euro AI spins up a storm in the BOC in about 12 days. Similar to what the GFS has been showing from 99L Something to keep an eye on.
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Re: ATL: INVEST 99L - Models

#14 Postby Stratton23 » Wed Aug 20, 2025 6:07 pm

GFS continues to show the ghost of 99L really taking a track far south in the caribbean as just a weak wave axis, but as the trade winds slow down in the W. Caribbean it is again showing “ 99L” trying to consolidate into a system at day 9-10
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Re: ATL: INVEST 99L - Models

#15 Postby Cpv17 » Wed Aug 20, 2025 6:15 pm

Stratton23 wrote:GFS continues to show the ghost of 99L really taking a track far south in the caribbean as just a weak wave axis, but as the trade winds slow down in the W. Caribbean it is again showing “ 99L” trying to consolidate into a system at day 9-10


Need to see more ensemble support. It’s definitely a possibility though.
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Re: ATL: INVEST 99L - Models

#16 Postby Powellrm » Wed Aug 20, 2025 6:19 pm

Stratton23 wrote:GFS continues to show the ghost of 99L really taking a track far south in the caribbean as just a weak wave axis, but as the trade winds slow down in the W. Caribbean it is again showing “ 99L” trying to consolidate into a system at day 9-10


This will be a fascinating one to keep an eye on. Although I’m not surprised anymore to see a system defy various models, but it’s always exciting to watch them develop despite the projection.
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Re: ATL: INVEST 99L - Models

#17 Postby Stratton23 » Wed Aug 20, 2025 7:11 pm

18z AIFS ensemble is definitely more bullish with this one developing in the NW caribbean in the 9-10 day range
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Re: ATL: INVEST 99L - Models

#18 Postby LAF92 » Wed Aug 20, 2025 7:59 pm

Stratton23 wrote:18z AIFS ensemble is definitely more bullish with this one developing in the NW caribbean in the 9-10 day range

18z GEFS ensembles are more bullish also
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Re: ATL: INVEST 99L - Models

#19 Postby kevin » Thu Aug 21, 2025 5:48 am

Not sure what's keeping them from designating this. Either way, the Euro is showing more members with development and seeing how 99L has defied model expectations for the better so far I have a feeling this one will get named eventually anyways. Will likely get quite an extension of its lifetime in post-season in that case.

Image
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Re: ATL: INVEST 99L - Models

#20 Postby USTropics » Thu Aug 21, 2025 8:40 am

kevin wrote:Not sure what's keeping them from designating this. Either way, the Euro is showing more members with development and seeing how 99L has defied model expectations for the better so far I have a feeling this one will get named eventually anyways. Will likely get quite an extension of its lifetime in post-season in that case.

https://i.imgur.com/2A9YPLx.png


I agree, there is enough evidence from microwave and ascat that this had a closed circulation and persistent convection for 24+ hours. I also understand the NHC's perspective—yesterday's model runs stretched out the vorticity sooner, and the persistence was not expected. Here is the trend of the last 4 ECMWF operational runs:
Image

I still do believe this will open back up into a trough here shortly (later this evening or tomorrow morning imo). This forecasted sounding 24 hours later gives all the clues:

1) Dewpoint IQR is separated from the temperature plot, especially at the mid levels (600-800 hPa) where it 'bows out' (i.e., significant dry air at this level)
2) Directional shear values are increasing, flattening out the vorticity maxima into a streamer (i.e., wave opens back up into a trough axis)

Image

Another good way of looking at this is using integrated water vapor transport (IVT) products. Alicia Bentley has a really good one on her model page (https://www.atmos.albany.edu/student/ab ... e=IVT_conv). This product has 700 hPa height contours plotted to give an idea of steering, shaded is IVT with IVT vectors overlayed (a healthy system has CCW rotation, or counter-clockwise rotation). We can see how 99L is easily trackable in the beginning on the 06z GFS, but becomes so disrupted it just is integrated with the trade wind flow into the Caribbean:

Image
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