Invest 94L—80% 2 day and 90% seven day odds of development

[NC US Geological Survice]

TriPol, Humberto doesn't kick so much as the other system escapes.

Deepmind 18z suggests the position of 94L relative to Humberto, once 94L reaches about Nassau, is the key to its landfall prospects. At 26-27°N, if it's a little faster and north of due west from Humberto, some members reach SC as early as Monday night. Slower members get no farther than 28°N (about Cape Canaveral's latitude) before getting sucked toward Humberto and OTS. To my eye, it looked like a 50/50 split. 

Here's my take: if Humberto becomes a major east of the Bahamas, and it moderately scoots NW while growing in size, whatever 94L becomes after getting over Hispanola is gonna put on some brakes due to Fujiwhara. That's why I don't see the low making a CONUS landfall in the cards; for us in the SE U.S., the effects are then limited to coastal erosion from the two systems and maybe several inches for whoever sits along the Carolina coasts nearest the low as it gets yoinked east. 

 

[olafminesaw]

2 hours ago, TriPol said:

I don;t understand the physics of how Humberto kicks the other system into the east coast. 

It doesn't, last night's run of the Euro has a stronger blocking high over Humberto slowing it down and allowing 94L to be pulled into the coast by the ULL. Without Humberto 94L would have a higher chance of landfall

 

[NorthHillsWx]

6z GFS slams the storm into the Carolina’s as a hurricane 

[MJO812]

7 minutes ago, NorthHillsWx said:

6z GFS slams the storm into the Carolina’s as a hurricane 

 

[NC US Geological Survice]

T-storm consolidation south of Hispanola now, in the Caribbean. 

[NorthHillsWx]

Really thinking the odds of this affecting the SE coast are increasing. A weaker Humberto/further separation increases risk further. If Humberto wasn’t there this is going into coast. Still a lot on the table and until a center forms there isn’t a clear solution but the trend on ensembles is clear and we’re seeing ops follow suite. Everyone from northern Florida to the OBX needs to be alert

[Newman]

The trend in the recent GFS and Euro runs has clearly been towards a stronger HP system over the top of Humberto, which effectively allows it to strengthen faster, move slower, and travel more on a west-northwest heading vs purely northwest. This allows for greater spacing between 94L and Humberto, it "escapes" out ahead of Humberto without any real fujiwhara or interactions.

 

Humberto plays a big role in the final evolution of 94L. How quickly 94L can develop once crossed over Hispaniola also is huge, but we don't know that yet. Until a well-defined center of circulation and system is there, there's lots of uncertainties

[WxWatcher007]

Just now, WxWatcher007 said:

I now believe that Invest 94L is a bona fide threat to the U.S. East Coast. 

Still, there is enormous uncertainty regarding the intensity and track of what is likely to become Imelda in the coming days. 

First, let's take a look at Humberto, which will play a critical role in the track of 94L. Although still sheared with the center likely west of the deeper convection, this tropical storm is on a clear organizing trend. 

The spacing between Humberto and 94L has been a point of discussion for days now. How close these two get will determine whether there will be a binary interaction. 

The GFS, which after sniffing out the potential for TC development in the SW Atlantic then kind of got lost in trying to consolidate the two waves, has clearly trended toward the Euro--to the extent you can with this much uncertainty in the setup. These are the last 5 GFS runs. 

Note how the trend has been two-fold. First, there is the obvious change that makes 94L stronger. That decreases the likelihood that it is absorbed by Humberto and given an escape route OTS. The second change is the spacing. It's subtle, but can be seen easily. A stronger and more organized 94L would likely have the outflow necessary to keep Humberto at bay. 

On the Euro, you see a similar trend with regard to spacing. Note how the escape routes of 1) Humberto and 2) NW flow in New England and SE Canada are blocked. These are the last 3 runs--not including this morning's 06z op run which continues the trend. 

The spacing difference is more than enough here to limit the impact of Humberto. 

Are we guaranteed a SE coast hit? Not at all. There are a lot of nuances remaining, including how quickly Humberto intensifies and its forward speed, the amplitude of the ridge and how it develops, and the amplitude of the cutoff over the CONUS. 

It is very clear, however, that 94L is poised to develop, and it poses a risk to at least the SE coast with regard to a direct hit, with possible impacts further north depending on track. 

 

Reposting here. 

[MJO812]

[olafminesaw]

The interaction of the two storms and the ULL could lead to some nasty flooding. I don't like that models are starting to pick up on a stalled  moisture feed 

[shaggy]

3 hours ago, NC US Geological Survice said:

T-storm consolidation south of Hispanola now, in the Caribbean. 

Better spin looks north of the island to me. Might take a while for a center to settle and write could see some jumps and relocations

[olafminesaw]

I do believe we can have very little confidence in models until Saturday when 94L really starts to develop. This reminds me in some ways of Joaquin, which missed the trough leading to hundreds of miles of track error 4-5 days out. Totally different set up, but just as if not more complex this time

[WxWatcher007]

 

[MJO812]

Gfs rolling 

[MJO812]

SC landfall on gfs

[WxWatcher007]

Some of the second tier models still have a binary interaction that pulls future Imelda away, but with the Euro/GFS/AI models aligning at least right now that increases the risk to the coast substantially imo. Still, any one solution is far from guaranteed.

[olafminesaw]

[Torch Tiger]

ICON (trash, I Know) is most wild, gives Bermuda two hits within 48 hours. 

[WxWatcher007]

1 minute ago, olafminesaw said:

I was just going to post—no surprise being just over 100 hours out but the GEFS essentially follow the op but with more of a NC threat. Everything is still on the table but I’m not convinced this hooks well into SC. I think that’s an unusual track climatologically speaking. 

[Torch Tiger]

25 minutes ago, WxWatcher007 said:

Some of the second tier models still have a binary interaction that pulls future Imelda away, but with the Euro/GFS/AI models aligning at least right now that increases the risk to the coast substantially imo. Still, any one solution is far from guaranteed.

12z gefs mostly into SC or NC, though haven't seen past hr 108

[Newman]

The trend in the forward motion of 94L is perhaps one of the biggest changes in the past day or so. The GFS went from having it buried in the Bahamas late Sunday/early Monday to being 12 hours away from a Carolinas landfall at that same time. This has certainly helped with the questions regarding interactions between 94L and Humberto. Such a faster 94L eliminates really any fujiwhara conversations. But, we are still within the 4-5 day range where I wouldn't take much off the table yet, other than perhaps a northern Mid-Atlantic and New England hit with such strong confluence present up there

[olafminesaw]

11 minutes ago, WxWatcher007 said:

I was just going to post—no surprise being just over 100 hours out but the GEFS essentially follow the op but with more of a NC threat. Everything is still on the table but I’m not convinced this hooks well into SC. I think that’s an unusual track climatologically speaking. 

I think as Newman alludes to above it's all about the timing. A faster system will be more of a NC/VA threat, the slowest solutions gets pulled OTS and somewhere in between makes that left hook into SC as it feels the pull of Humberto just a little bit. That is the most delicate balancing act so I agree it is probably the least likely.

[NorthHillsWx]

One other note that I’ve seen on recent modeling suggests a more favorable pattern for strengthening with a divergent flow aloft and less dry air. Actually somewhat concerned this could be a strong hurricane now. So much has changed over last couple days

[stormwatcherJ]

My worry for the NC/SC coast is that this could creep up on them quickly. It's not even a tropical storm yet and might not become a hurricane until getting really close to NC/SC. If it moves fast and has a round of rapid intensification, this could happen just before landfall. This is not gonna be some long tracker we're following for a week.. situations are gonna develop in real time. 

[GaWx]

12Z UKMET: At hour 120, 993 mb Humberto, which is within only 500 miles ENE of 1000 mb 94L, causes 94L (which had been moving mainly NNW) to then get sucked toward it as 94L then suddenly turns SSE, then ESE, and then ENE to well OTS (near 27N, 72W)

NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER 54 HOURS
FORECAST POSITION AT T+ 54 : 21.1N 76.5W

LEAD CENTRAL MAXIMUM WIND
VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS)
-------------- ---- -------- ------------- -------------
0000UTC 28.09.2025 60 22.2N 76.2W 1006 31
1200UTC 28.09.2025 72 23.5N 76.9W 1006 32
0000UTC 29.09.2025 84 24.1N 77.4W 1004 33
1200UTC 29.09.2025 96 25.9N 78.3W 1004 39
0000UTC 30.09.2025 108 25.8N 77.8W 1002 38
1200UTC 30.09.2025 120 26.4N 78.1W 1000 37
0000UTC 01.10.2025 132 25.4N 77.6W 999 37
1200UTC 01.10.2025 144 25.0N 76.5W 997 43
0000UTC 02.10.2025 156 25.4N 74.8W 995 46
1200UTC 02.10.2025 168 26.9N 72.2W 991 47

——————
So far at 12Z for major operationals

-GFS hits just S of Georgetown, SC, Mon PM (9/29) as a H (with strong support from GEFS, it’s most ominous run by far yet for SE US)
-Icon, UKMET, CMC thanks to Fujiwhara go safely OTS from SE US
-Euro next
-JMA only out to 72 so far (can’t tell yet)

[GaWx]

1 hour ago, WxWatcher007 said:

Some of the second tier models still have a binary interaction that pulls future Imelda away, but with the Euro/GFS/AI models aligning at least right now that increases the risk to the coast substantially imo. Still, any one solution is far from guaranteed.

Also, the UKMET, one of the top tier models, interacts with Humberto and goes well OTS from the SE US per my post above this.

[GaWx]

12Z Euro

[wthrmn654]

15 hours ago, WxWatcher007 said:

What was 12z and 18z?

Reminder, this link give you an interactive and interactive map of hurricane and invests, and can plot every single model run guidance wise. Can all be overlayed as well. 

The first product is one being referenced 

 https://vlab.noaa.gov/web/osti-modeling/hfip/products

[Torch Tiger]

Euro AI does what I was going to mention as a possibilty earlier; stalls twice and even completes a small loop at some point?  I think there is some validity to that, at least the entry point; either a very slow approach or full-on stall.

Some of these modeled interactions are wild, and I'd toss.  

[stormwatcherJ]

1 minute ago, Torch Tiger said:

Euro AI does what I was going to mention as a possibilty earlier; stalls twice and even completes a small loop at some point?  I think there is some validity to that, at least the entry point; either a very slow approach or full-on stall.

I never like to hear the word "stall" when talking about a hurricane approaching the NC/SC coast. That's always the most catastrophic scenario. Rain, rain, more rain.