Invest 94L—20% 2 day and 60% seven day odds of development

[WxWatcher007]

The tropics are active now with three systems being monitored. This is the thread for the current orange nearing the Leeward Islands. 

 

The forecast for this wave is complicated, with more implications for land than our central Atlantic cherry. The signal for development is not as strong as the Atlantic cherry, but this morning there is a modest amount of convection.

 

The key to this wave and its possible risk to land is that it is likely to stay weak as it pushes across the northern Leeward Islands, bringing rain and gusty winds, but it finds a potentially more favorable environment for development in the southwest Atlantic. While the GFS has led the way in signaling development, in its latest run it consolidates both waves in five days off near the Bahamas.

 

Meanwhile, the Euro, which was more bearish originally, keeps both waves separate.

 

It is critical to see how the upper level pattern over the east coast develops, and whether the strength and orientation is enough to kick both waves out to sea or create an east coast threat. This one is definitely worth watching. 

[GaWx]

 This was a TC on the admittedly untrustworthy GFS as far back as the 0Z 9/18 run and consistently on runs the last couple of days, including some ensemble members. Also, the Icon and Euro have at least hints that this may turn into something.

[MJO812]

Cmc now has it but it doesn't gain any attitude after this due to confluence. Gfs is similiar. 

[GaWx]

12Z GEFS: another pretty active run

[marsman]

55 minutes ago, MJO812 said:

Cmc now has it but it doesn't gain any attitude after this due to confluence. Gfs is similiar. 

Pushes it south after this if I’m looking at the right one. We could use the rain, but please not another Florence. 

[GaWx]

The brand new (12Z) Euro has this on 9/29 hit NC as a TD.

[WxWatcher007]

13 minutes ago, GaWx said:

The brand new (12Z) Euro has this on 9/29 hit NC as a TD.

Might be a weak TS verbatim but as you know it’s more important to see the steering patterns that trough is really what make this a land threat as a ridge builds over the top and it’s not crazy far out—only about a week away. Short fuse system. 

[WxWatcher007]

East of the Leeward Islands:
A tropical wave located about 250 miles east of the Leeward Islands 
is producing disorganized showers and thunderstorms.  Environmental 
conditions appear marginally conducive for some development over the 
next few days as the wave moves quickly westward to 
west-northwestward at 15 to 20 mph.  By the latter part of this 
week, the system is expected to slow down and turn northwestward, 
and a tropical depression could form late this week when the system 
is over the southwestern Atlantic Ocean or near the Bahamas.  
Regardless of development, gusty winds and heavy rainfall are 
expected to affect portions of the Leeward Islands late tonight and  
Tuesday and near Puerto Rico late Tuesday and Wednesday.
* Formation chance through 48 hours...low...10 percent.
* Formation chance through 7 days...medium...50 percent.

 

[GaWx]

18Z Euro has a 1001 TS headed NNW in the direction of NC at 30N, 75W at 144

[MJO812]

4 minutes ago, GaWx said:

18Z Euro has a 1001 TS headed NNW in the direction of NC at 30N, 75W at 144

Right after the gfs went way right lol

[GaWx]

0Z Euro has a 1006 TS hit NC 9/29

[WxWatcher007]

The Euro trend has been toward a more robust system, with 06z showing a strong storm.

What’s far more important however for a D6 forecast is the Euro continues to show a cutoff low over the southeast with a ridge building over the top of the eastern U.S., effectively guaranteeing a bona fide east coast threat. Here, it looks like the trough to the east (top right of image) is not enough to kick this out to sea. AI models in general support this upper level configuration too.

Now, before coastal folks get too concerned, there’s still a LOT to sort out because while the cutoff looks legit, we don’t know where it’ll be, the location of the ridge, and how much, if any, an escape window opens. There’s also the big question of how the spacing of the three systems—Gabrielle, 93L, and 94L, impact track and intensity of 94L.

Now that this is an invest, the additional resources will help us nail this down. This one is worth more than a casual eye.

[WxWatcher007]

3 minutes ago, Wannabehippie said:

94L is a mess right now, convection is being blown to the south

blob:https://www.tropicaltidbits.com/8eb8282d-d465-4233-8984-b4cec830516f

 

 

That’s expected. Note that little upper level low to the west. It’s pretty robust, showing just how busy things are. Not a lot of spacing.

Shear will be an issue for a few days I think but the guidance is showing a stronger environment for development near the Bahamas eventually. Still, a lot to sort out there as @NorthHillsWx noted some potential roadblocks earlier. 

[GaWx]

94L

6Z Euro at 144 had a strengthening 998 TS moving NNW N of the Bahamas threatening the SE US.

6Z Icon at 120 was well E of Euro

6Z GFS had nothing from this, alone, although it appears to combine its vorticity with 93L and develop that well offshore

—————-

No UK run has had this as a TC AFAIK as of then. But 12Z UK: TD in NW Bahamas that drifts NE

NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER 138 HOURS
FORECAST POSITION AT T+138 : 25.0N 77.1W

LEAD CENTRAL MAXIMUM WIND
VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS)
-------------- ---- -------- ------------- -------------
1200UTC 29.09.2025 144 25.6N 76.9W 1010 30
0000UTC 30.09.2025 156 26.0N 76.2W 1009 24
1200UTC 30.09.2025 168 26.9N 74.2W 1008 27

[NorthHillsWx]

11 minutes ago, GaWx said:

94L

6Z Euro at 144 had a strengthening 998 TS moving NNW N of the Bahamas threatening the SE US.

6Z Icon at 120 was well E of Euro

6Z GFS had nothing from this, alone, although it appears to combine its vorticity with 93L and develop that well offshore

—————-

No UK run has had this as a TC AFAIK as of then. But 12Z UK: TD in NW Bahamas that drifts NE

NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER 138 HOURS
FORECAST POSITION AT T+138 : 25.0N 77.1W

LEAD CENTRAL MAXIMUM WIND
VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS)
-------------- ---- -------- ------------- -------------
1200UTC 29.09.2025 144 25.6N 76.9W 1010 30
0000UTC 30.09.2025 156 26.0N 76.2W 1009 24
1200UTC 30.09.2025 168 26.9N 74.2W 1008 27

As complicated a tropical development setup as you’ll ever see. Multiple competing waves, ULL progression, SE trough, a cat 4 hurricane nearby… Good luck making a call and standing on it with this setup 

[GaWx]

 12Z Euro: After forming in the Bahamas, it recurves away from the SE US and the center just misses Bermuda to the NW as it did for 93L two days earlier in this run. Then it turns back NW before ultimately turning back NE missing the NE US and barely missing Newfoundland.

[MJO812]

40 minutes ago, GaWx said:

 12Z Euro: After forming in the Bahamas, it recurves away from the SE US and the center just misses Bermuda to the NW as it did for 93L two days earlier in this run. Then it turns back NW before ultimately turning back NE missing the NE US and barely missing Newfoundland.

Interesting runs coming up

 

[shaggy]

46 minutes ago, GaWx said:

 12Z Euro: After forming in the Bahamas, it recurves away from the SE US and the center just misses Bermuda to the NW as it did for 93L two days earlier in this run. Then it turns back NW before ultimately turning back NE missing the NE US and barely missing Newfoundland.

Would make sense there would be a weakness to 94ls east with 93L being so close. Think we would be having a different conversation with no 93 L in the picture