ATL: Ex INVEST 99L - Discussion

[AJC3]

0Z Best Track:

AL, 99, 2025082400, , BEST, 0, 121N, 521W, 35, 1010, DB

Whoa mama!

Does this mean that this will be declared a tropical depression at 11 o’clock?

No circulation exists.

No circulation = no TC

Exactly. One point to be made is that the fact that the disturbance is currently BT'd as having 35kt winds increases the chance that this would be designated as a PTC, since it would be more likely to produce TS conditions in the Lesser Antilles. That way, it would allow NHC to issue Watches/Warnings for TS conditions.

[StormWeather]

Does this mean that this will be declared a tropical depression at 11 o’clock?

No circulation exists.

No circulation = no TC

Exactly. One point to be made is that the fact that the disturbance is currently BT'd as having 35kt winds increases the chance that this would be designated as a PTC, since it would be more likely to produce TS conditions in the Lesser Antilles. That way, it would allow NHC to issue Watches/Warnings for TS conditions.

Yeah, I could see PTC advisories initiated at 11 pm. Definitely fits the criteria. I think early this season before the season started the NHC changed the hours in advance of TS conditions being anticipated and putting out advisories from 48 hours to 72 hours. That means even more extended lead time.

[BobHarlem]

Looking here I don't see the NHC really doing anything with this until recon is out there, if then. Probably will keep it at 40% overnight.

[eastcoastFL]

Looking here I don't see the NHC really doing anything with this until recon is out there, if then. Probably will keep it at 40% overnight.

https://i.postimg.cc/LXYjTWbV/15281184.gif

I don't see much there for the NHC to write about. An elongated wave axis with no real circulation. Still just a strong wave with potential to be more down the road.

[Woofde]

0Z Best Track:

AL, 99, 2025082400, , BEST, 0, 121N, 521W, 35, 1010, DB

Whoa mama!

Does this mean that this will be declared a tropical depression at 11 o’clock?

No circulation exists.

No circulation = no TC

Yeah, it's still a bit messy at the moment. The shear isn't killing it, but it will still be difficult to consolidate a circulation under these conditions.

The tenacity of this wave is really admirable though. When you read the genesis outlooks for this guy over the past week they are harsh. One would've thought it should've long poofed by now, but it's still here kicking.

[abajan]

6Z Best Track:

AL, 99, 2025082406, , BEST, 0, 123N, 541W, 35, 1010, DB...

[Weatherwatcher2018]

Do you think it will be upgraded this morning

[Ubuntwo]

Do you think it will be upgraded this morning

Not this morning - there is no evidence of a closed circulation at the moment. If it is upgraded today, it will be in the evening dependent on recon findings.

[BobHarlem]

Do you think it will be upgraded this morning

No chance, LLC isn't there.

from the 8am outlook:

East of the Windward Islands (AL99):
Showers and thunderstorms associated with a tropical wave located
about 200 miles east of the Windward Islands have increased since
yesterday. However, the wave does not appear to have a surface
circulation. This system could still become a tropical depression
during the next day or two while it moves quickly westward at about
20 to 25 mph, passing through the Windward and Leeward Islands
later today and early Monday. Regardless of development, locally
heavy rainfall and gusty winds are likely across portions of the
Windward and Leeward Islands today and Monday. The system is
expected to reach the central Caribbean Sea on Tuesday, where
conditions are forecast to become less favorable for additional
development. An Air Force reconnaissance aircraft is scheduled to
investigate the system this afternoon, if necessary.
* Formation chance through 48 hours...medium...40 percent.
* Formation chance through 7 days...medium...40 percent.

-
They are basically waiting on recon. If I were to take a guess right now I doubt it gets upgraded at all, but I think recon will be there at a good time to make sure. Mid levels fairly healthy. It is showing up now on Barbados radar.




Barbados weather radar https://www.barbadosweather.org/Radars/ ... oducts.php

Cyclonixwx tries to get something here on radar too https://cyclonicwx.com/storms/al99/

[Cachondo23]

Can the NHC initiate a PTC for a wave with 40% of development?

[TallyTracker]

We’ve seen waves with 50 kt (60 mph) sustained winds before that struggled to develop a closed circulation in the MDR and Caribbean.

Hurricane Dolly in 2008 is a great example as the circulation was not well defined until the western Caribbean but still hit Texas as a hurricane. The storm had TS winds for much of it’s trek across the Caribbean.

[BobHarlem]

Can the NHC initiate a PTC for a wave with 40% of development?

Can they? yeah, will they? not with this, it just doesn't qualify. (See Erin in the Cabo Verde) I wouldn't be shocked to see it get all the way to central America in this half baked state and never develop.

[DunedinDave]

It’s really motoring. Moving very fast. I just wonder if it is moving too fast to 1) develop and 2) Turn. Feels like this we’ve seen this song and dance before with “speedboat storms” heading into the Caribbean that crash right into CA. Obviously models are showing this right now.

[Kingarabian]

How it looks when it reaches the vicinity of Jamaica is key. If it remains this robust, it could slow down and gradually track WNW. That opens the door for development near the Yucatan.

[Kingarabian]

The models have been killing this off prematurely all last week. Now they're keeping it coherent until it passes the windward islands, then forecast its vorticity to fracture thus allowing it to crash into Central America.

[TampaWxLurker]

Moving too quickly west for its own good. Can't get any time to consolidate.

[Weathertracker96]

The models have been killing this off prematurely all last week. Now they're keeping it coherent until it passes the windward islands, then forecast its vorticity to fracture thus allowing it to crash into Central America.

I agree with you. It’s best to watch this in real time. It’s not even supposed to be here according to the models all last week. It’s a persistent wave.

[Nimbus]

How it looks when it reaches the vicinity of Jamaica is key. If it remains this robust, it could slow down and gradually track WNW. That opens the door for development near the Yucatan.

NHC said this was tracking west at between 20 and 25 mph till about Jamaica.
Forward speed like that makes it tougher to detect a west wind at the least.
Which end of the wave will close off?
There is about 4 degrees of latitude there, I can't see the apex of the wave at the moment.

[TomballEd]

How it looks when it reaches the vicinity of Jamaica is key. If it remains this robust, it could slow down and gradually track WNW. That opens the door for development near the Yucatan.

NHC said this was tracking west at between 20 and 25 mph till about Jamaica.
Forward speed like that makes it tougher to detect a west wind at the least.
Which end of the wave will close off?
There is about 4 degrees of latitude there, I can't see the apex of the wave at the moment.

The fast speed also increases shear *and* reduces low level convergence. Plenty of upper divergence, not much low level convergence. I think recon is flying, I am surprised, I see no evidence of a closed low on vis satellite.

[zhukm29]

Interesting thread by meteorologist Yaakov Cantor about how the short term organization of 99L now could affect how conditions will be like in the Western Caribbean. A more organized 99L could spell trouble later on.
 https://x.com/yconsor/status/1959526535108382799



Apparently 99L might have a small closed circulation already? Luckily we have recon today to and investigate - if it can find a LLC, this will likely jump straight to Gabrielle given it already has 35kt winds. ASCAT does have lower resolution, and we've have cases before where ASCAT showed a wave but recon found a LLC (e.g., Nana 2020 is a good example when it was designated; it had a LLC that was not reflected on ASCAT due to its small size and fast forward speed). We've also seen a lot of short lived spin-ups in this area in previous seasons, so I don't think anyone can take their eyes off of this wave, especially with how persistent it is. I do think the window of opportunity for 99L to claim a name is closing though as it enters the Eastern Caribbean graveyard, at least in the short term.
 https://x.com/yconsor/status/1959529674175897818