Major Hurricane Helene

[WxWatcher007]

Given the current discussion in the main thread, the increasing confidence in a TC developing, and the threat of U.S. impacts within the next 7 days, I think it's time to break out discussion of our current area of interest in the western Caribbean into a separate thread. 

Northwestern Caribbean Sea and Gulf of Mexico:
A broad area of low pressure is likely to form by the early to 
middle part of next week over the northwestern Caribbean Sea and 
the adjacent portions of Central America.  Thereafter, gradual 
development of this system is possible, and a tropical depression 
could form as the system moves slowly to the north or northwest 
over the northwestern Caribbean Sea and across the Gulf of 
Mexico through the end of next week.  Regardless of development, 
this system is expected to produce heavy rains over portions of 
Central America during the next several days.
* Formation chance through 48 hours...low...near 0 percent. 
* Formation chance through 7 days...medium...60 percent.

 

We've been tracking this for a while, and as I mentioned before our favorable homebrew region pattern that led to several invests off the East Coast and Hurricane Francine in the Gulf due to stalled frontal boundaries and trough interaction has evolved this week to a Central American Gyre (CAG) pattern characterized by broad cyclonic flow over the eastern Pacific, Central American land mass, and western Caribbean. 

 

The result is a growing amount of vorticity which we're starting to see in the region. This is an analysis at 850mb. 

As a trough digs into the region, we get a favorable setup for upper divergence, which aids the development of convection, which will likely continue to pulse until we can start seeing a complex of storms become more persistent. 

 

It's unclear if today's convection is the start of this process.

 

TCs that come out of CAGs usually start as broad systems that slowly develop. That's partly a function of being in a broader cyclonic flow. However, once the TC establishes itself, depending on the intensification environment they can have a variety of upper bound or lower bound ceilings. 

There's strong cross guidance support in both the operational models and ensembles that something develops in the Western Caribbean or Gulf in the coming days, and is drawn north toward the U.S. coast. 

 

There are a lot of options on the table. First, with intensity, it's unclear how quickly any potential TC will organize to take advantage of what looks like a favorable environment for intensification. The GFS on balance has been more aggressive, while the Euro has been least aggressive. 

Secondly, with track, while it looks like the central and eastern Gulf are looking most likely to be in a possible landfall zone, there are questions about what happens with the steering pattern both before and after a landfall. The general pieces on the board are identified--a western ridge and eastern U.S. trough, but it's unclear how timing and amplitude will shake out and influence the eventual track. Here's a trend gif at 500mb looking at the GFS and Euro respectively. 

 

Bottom line is there is a lot of uncertainty with this system. While genesis is likely, we still have questions on eventual intensity, landfall location, and overall track afterward, which could impact the central, southern, or eastern sections of the country. 

Given the broad and likely moisture laden characteristics of the system, surge and rainfall are likely to be significant impacts. Folks all along the Gulf coast should be watching this closely. 

[CurlyHeadBarrett]

Chances of this taking advantage of the shear?

[GaWx]

12Z Euro: 991 Pensacola Fri night
12Z UKMET: 1000 FL panhandle Fri night

12Z Icon: 999 E LA Fri night

12Z GFS: 998 Panama City Thu night

12Z CMC: 993 Mobile late Thu afternoon

[StantonParkHoya]

Models have definitely tightened up today

[StantonParkHoya]

3 minutes ago, CurlyHeadBarrett said:

WDYM tightened up

All I'm seeing is fucking downtrending EVERY SINGLE TIME

I’m talking about spread on landfall location

[GaWx]

17 minutes ago, CurlyHeadBarrett said:

FFS and they were predicting shit like 930 yesterday?

These operationals were not predicting anywhere near 930. The lowest yest was 963 on 6Z GFS. But anyway, good for Gulf coast to not have 930. Being not far from the coast, I can empathize. Slop is good. And don’t be fooled by strength. Flooding rains can happen with a TS or even unnamed like was the case in NC recently. And even a cat 1 H can cause sig damage near center.

[GaWx]

6 minutes ago, CurlyHeadBarrett said:

I saw the navgem

Bad model. JMA better..it has 1003 moving little in Bay of Campeche at 192!

[cptcatz]

16 minutes ago, GaWx said:

These operationals were not predicting anywhere near 930. The lowest yest was 963 on 6Z GFS. But anyway, good for Gulf coast to not have 930. Being not far from the coast, I can empathize. Slop is good. And don’t be fooled by strength. Flooding rains can happen with a TS or even unnamed like was the case in NC recently. And even a cat 1 H can cause sig damage near center.

Also tornado threat with these big broad tropical storms moving into the gulf coast.

[NorthHillsWx]

Really a hostile environment showing up in northern GOM across modeling. 25-30kts shear and dry air lurking. 

[CurlyHeadBarrett]

Just now, NorthHillsWx said:

Really a hostile environment showing up in northern GOM across modeling. 25-30kts shear and dry air lurking. 

 

Why?

[NorthHillsWx]

22 minutes ago, CurlyHeadBarrett said:

Why?

A couple reasons- 1 being the the trough is being modeled as more progressive and slightly stronger so it picks up whatever forms and whisks it to to the NE while imparting strong westerly shear snd 2 the surge of drier air behind the trough is more entrained into the system. Another half-a-storm incoming, if todays modeling proves correct

[MANDA]

At this point it does not look like a significant ACE producer.  We will get another named system and like 6 of the 7 named storms so far this season it will find land which is pretty impressive.  Land interactions and Beryl are the highlights of this season so far, IMO.

Worth watching for sure in the days ahead but not seeing blockbuster potential with this.  Perhaps a situation similar to Francine as far as intensity.  SST's are way warm but not seeing super favorable conditions aloft, at least at this point.   

We'll see where we are at the end of September but something along the lines of average number of named storms and ACE would be my call right now as we move through the second half of the season. 

[CurlyHeadBarrett]

Just now, MANDA said:

At this point it does not look like a significant ACE producer.  We will get another named system and like 6 of the 7 named storms so far this season it will find land which is pretty impressive.

Worth watching for sure in the days ahead but not seeing blockbuster potential with this.  Perhaps a situation similar to Francine as far as intensity.  SST's are way warm but not seeing super favorable conditions aloft, at least at this point.   

We'll see where we are at the end of September but something along the lines of average number of named storms and ACE would be my call right now as we move through the second half of the season. 

 

What is prohibiting this from being a blockbuster

[MANDA]

3 minutes ago, CurlyHeadBarrett said:

What is prohibiting this from being a blockbuster

From my point of view I'm not seeing a modeled large anticyclone aloft and as @NorthHillsWx noted possible less than favorable trough interaction.

[CurlyHeadBarrett]

2 minutes ago, MANDA said:

From my point of view I'm not seeing a modeled large anticyclone aloft and as @NorthHillsWx noted possible less than favorable trough interaction.

Is the trough digging too deeply?

[cptcatz]

18z GFS coming in hot. 951 mb headed towards the Panhandle at h126

[CurlyHeadBarrett]

11 minutes ago, cptcatz said:

18z GFS coming in hot. 951 mb headed towards the Panhandle at h126

 

Sheeeeeit what made it uptick?

[purduewx80]

10 minutes ago, CurlyHeadBarrett said:

Sheeeeeit what made it uptick?

It organized more quickly in the Caribbean, had better ridging overhead and the position of the cut off over the Miss. Valley changed slightly, resulting in excellent ventilation. Tells us the cut off position and where/when a low organizes are probably the main reasons for the uncertainty. 

[CurlyHeadBarrett]

4 minutes ago, purduewx80 said:

It organized more quickly in the Caribbean, had better ridging overhead and the position of the cut off over the Miss. Valley changed slightly, resulting in excellent ventilation. Tells us the cut off position and where/when a low organizes are probably the main reasons for the uncertainty. 

So conditions might be more favorable?

[purduewx80]

2 minutes ago, CurlyHeadBarrett said:

So conditions might be more favorable?

Than what? The spread in the full ensemble suite is wildly different in terms of intensity, timing and placement. Anything from a tropical storm to a major hurricane is on the table. The blocking pattern over North America is adding to the uncertainty, unfortunately. Need to watch the thunderstorm cluster south of Jamaica tonight and the potential competition in the east Pac, too. The highest ocean heat content surrounding Central America is squarely on the Atlantic side, so it will be interesting to see if that is where convection ends up being favored the next few days. Bottom line, it’s complicated. Operational runs will continue to have wild swings, perhaps into Monday.

[CurlyHeadBarrett]

2 minutes ago, purduewx80 said:

Than what? The spread in the full ensemble suite is wildly different in terms of intensity, timing and placement. Anything from a tropical storm to a major hurricane is on the table. The blocking pattern over North America is adding to the uncertainty, unfortunately. Need to watch the thunderstorm cluster south of Jamaica tonight and the potential competition in the east Pac, too. The highest ocean heat content surrounding Central America is squarely on the Atlantic side, so it will be interesting to see if that is where convection ends up being favored the next few days. Bottom line, it’s complicated. Operational runs will continue to have wild swings, perhaps into Monday.

Than previous runs depicting a 998mb storm

[CurlyHeadBarrett]

mogs me

up to 70%

[GaWx]

18Z:

GEFS: centered on FL Big Bend

EPS: centered on Pensacola

[MJO812]

Icon is devastating 

 

[MJO812]

Gfs o boy

[GaWx]

7 minutes ago, MJO812 said:

Icon is devastating 

 

If this storm were to actually take a similar path with that strength moving at that speed, that would likely be very damaging well inland (including in my area and well beyond). Hope nothing like this happens. I’d much prefer the slop.

[GaWx]

4 minutes ago, MJO812 said:

Gfs o boy

[WxWatcher007]

Like @purduewx80 said earlier, these runs illustrate how wide the envelope of solutions still is. Looking at the 500mb trend and there is none really. The trough is kind of all over in placement, and there’s a huge difference in impacts and impact locations as a result.

The only thing that seems to be in better focus is that Florida looks like the primary landfall risk zone currently. 

[MJO812]

5 minutes ago, GaWx said:

Cmc is east of the past runs and hits FL panhandle but alot weaker than the gfs. Only 990.

[GaWx]

0Z UKMET: significantly stronger at landfall (993 vs 1000 on 12Z run) and 150 miles east of 12Z with a landfall late afternoon Friday in the FL Big Bend moving NNE; thankfully not nearly as strong as Icon/GFS but UK is notorious for being conservatively weak this far out, especially with winds but also with SLP and the trend is worrying:

NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER  84 HOURS
              FORECAST POSITION AT T+ 84 : 18.6N  85.7W

                        LEAD                 CENTRAL     MAXIMUM WIND
      VERIFYING TIME    TIME   POSITION   PRESSURE (MB)  SPEED (KNOTS)
      --------------    ----   --------   -------------  -------------
    1200UTC 25.09.2024   84  18.6N  85.7W     1003            34
    0000UTC 26.09.2024   96  21.3N  85.1W     1001            34
    1200UTC 26.09.2024  108  22.5N  85.8W      998            42
    0000UTC 27.09.2024  120  25.0N  84.6W      995            40
    1200UTC 27.09.2024  132  27.2N  84.3W      992            42
    0000UTC 28.09.2024  144  31.1N  83.0W      995            41
    1200UTC 28.09.2024  156  36.3N  82.7W     1000            23
    0000UTC 29.09.2024  168  39.6N  82.7W     1005            27