Major Hurricane Helene

[chris21]

3 hours ago, gopack42 said:

I understand there is tons of uncertainty in track and intensity for the approach to the gulf coast, but let's assume it comes on shore and tracks up the Appalachians (or close to it).  My question is, up in the SC and NC mountains at higher elevations (3500 ft and higher), do storms typically have stronger wind impact for higher elevations even though the cyclone is winding down post landfall?  I wasn't sure if elevation correlates to stronger winds even as the storm winds down.  Thanks very much for any knowledge on this.  

I camped on top of Mt. Sterling at 6000 feet in June of 2007 during a tropical depression and it was wild. 60 mph winds easy. Wouldn’t recommend it. I just moved to a location just below Roan Mountain on the NC/Tenn border at 3800 feet so hoping it goes well west.

[Jebman]

With the speed this system may move at, maybe the Washington Metropolitan Region gets a good strong wind/torrential rain hit off of it.

[jburns]

2 hours ago, wthrmn654 said:

Where do I send my thank you money check to you!?!?

You’re very welcome.  You can’t afford me so I do it for free.

[GaWx]

0Z GFS also looks to come in a good bit E of its prior runs. The upper low, similar to the case for the 0Z Icon, is further E.

 Confirmed: 948 mb left side of Big Bend late Thu afternoon. Not nearly as far E as Icon and then tracks into N-C GA.

[GaWx]

0Z CMC similar to 12Z with Apalachee Bay at 973 mb late Thu afternoon followed by Atlanta 981 Thu night.

[GaWx]

0Z UKMET vs 12Z is perhaps slightly E/2 mb stronger (985) with landfall still near Apalachicola late Thu evening and then to Atlanta midday Fri:

NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER  24 HOURS
              FORECAST POSITION AT T+ 24 : 18.8N  83.0W

                        LEAD                 CENTRAL     MAXIMUM WIND
      VERIFYING TIME    TIME   POSITION   PRESSURE (MB)  SPEED (KNOTS)
      --------------    ----   --------   -------------  -------------
    0000UTC 24.09.2024   24  18.8N  83.0W     1002            32
    1200UTC 24.09.2024   36  18.9N  84.8W     1002            36
    0000UTC 25.09.2024   48  19.7N  85.1W      999            38
    1200UTC 25.09.2024   60  21.6N  86.2W      996            41
    0000UTC 26.09.2024   72  23.4N  86.3W      992            44
    1200UTC 26.09.2024   84  25.9N  85.3W      988            52
    0000UTC 27.09.2024   96  29.2N  84.8W      985            46
    1200UTC 27.09.2024  108  33.1N  84.1W      990            32
    0000UTC 28.09.2024  120  36.7N  85.4W      998            19
    1200UTC 28.09.2024  132  39.2N  87.9W     1003            24
    0000UTC 29.09.2024  144  39.8N  92.2W     1007            13
    1200UTC 29.09.2024  156              CEASED T

 

[GaWx]

0Z GEFS, with upper low being 250 miles E of 18Z, has its mean landfall 175 miles E of the 18Z’s Pensacola or just E of Apalachicola. The mean then instead of going NNW through AL travels N into SW GA. So, more/fewer members than last run in GA/AL although AL still has a decent # of members.

[GaWx]

Unlike GFS/Icon, the 0Z Euro doesn’t appear to be shifting E so far. Upper low not shifted E like on those. Landfall Apalachicola late Thu afternoon at 982. Goes near AL/GA line (W of ATL). 12Z went through ATL. 

[GaWx]

Hurricane models are way off the chart strong, but are they even useful yet since there’s not yet a definite LLC?

[Radtechwxman]

0z euro remaining very tame with little to no deepening up until landfall. What is its track record with hurricanes?

[Windspeed]

0z euro remaining very tame with little to no deepening up until landfall. What is its track record with hurricanes?

Use the global OPs for pattern and track, less so for intensity. The ECMWF is excellent for overall track guidance. Obviously, if the globals are significantly intensifying a system, it's worth noting. But it is better to use the TC models for intensity once we have an established tropical cyclone. Even still, err on the side of caution because TC models can way overdo the intensity on an invest that has yet to form a proper vorticity maximum. That's a bit of a tangent, so to just be clear, focus less on the global OPs for exact intensity and more for track of system. I'd stress even further that the ensembles means are much better at determining overall track three-to-four days out, especially prior to TCG, as it's still unclear where exactly that will occur for initial origin of track.

[Radtechwxman]

1 minute ago, Windspeed said:

11 minutes ago, Radtechwxman said:

0z euro remaining very tame with little to no deepening up until landfall. What is its track record with hurricanes?

Use the global OPs for pattern and track, less so for intensity. The ECMWF is excellent for overall track guidance. Obviously, if the globals are significantly intensifying a system, it's worth noting. But it is better to use the TC models for intensity once we have an established tropical cyclone. I say this because TC models can way overdo the intensity on an invest that has yet to form a proper vorticity maximum. That's a bit of a tangent, so to just be clear, focus less on the global OPs for exact intensity and more for track of system. I'd stress even further that the ensembles means are much better at determining overall track three-to-four days out, especially prior to TCG, as it's still unclear where exactly that will occur for initial origin of track.

Great analysis. Kind of my thought. Though shockingly GFS has overall been on board with a high end outcome. But like you said not really trusting intensity outcomes till we have a defined vorticity maximum and formation of a TD or TS. So far the gyre seems to be struggling to focus an area of concise vorticity. If this takes a while to organize, higher end outcomes are less likely to be realized. 

[GaWx]

0Z Euro ens: only very slight E shift and slightly faster; mean landfall is Apalachicola Thu evening; then it goes N into far W GA and then NNW into NE AL. W of GEFS mean.

[Windspeed]

[Floydbuster]

 

[purduewx80]

Still a mess at the surface, with multiple areas of convergence. Convection is firing over the southern piece but most models key in on the area west-southwest of Jamaica. Seeing scattered areas of 25-30KT winds in there. Hopefully NHC goes the PTC route later today if the low hasn’t consolidated yet. 

[beanskip]

How has the verification of the HAFS models been compared to the HWRF and HMON (which they are retiring, correct?)? 

I know the HWRF and HMON often overestimated intensification (although I also remember them being the first to catch on to the idea that Michael would blow up). 

Is the same a bias of the HAFS? Any track biases observed?

EDIT: I'm prompted to ask as I see the 6z HAFS-B down to 978mb before even reaching 20N. #gulp

[beanskip]

Well, to answer my own question, there damned well better still be a "overintensity" bias because the 6z HAFS-B is at 904 mb at 75 hours. 

[cardinalland]

10 minutes ago, beanskip said:

Well, to answer my own question, there damned well better still be a "overintensity" bias because the 6z HAFS-B is at 904 mb at 75 hours. 

Generally one waits until a depression has formed to rely on hurricane models, since a lot can change based on where the low forms and how long it takes to actually form. Hurricane models can overestimate intensity of a storm before it has formed because they sometimes assume the depression has already formed and that intensification can start immediately, when that is not the case.

[Seminole]

7 minutes ago, beanskip said:

Well, to answer my own question, there damned well better still be a "overintensity" bias because the 6z HAFS-B is at 904 mb at 75 hours. 

Hurricane models are not a good predictor of intensity without COC. They all over produce at this point. The Global models have all shifted east this morning. The ULL is further east and stronger.

[beanskip]

2 minutes ago, cardinalland said:

Generally one waits until a depression has formed to rely on hurricane models, since a lot can change based on where the low forms and how long it takes to actually form. Hurricane models can overestimate intensity of a storm before it has formed because they sometimes assume the depression has already formed and that intensification can start immediately, when that is not the case.

Oh I know that. I'm asking about the biases of the HAFS vs. the retiring models. 

[bdgwx]

Tomer Burg's super ensemble is focusing a possible landfall in the big bend area of Florida.

[hawkeye_wx]

It is likely the very intense hurricane models are organizing the system too quickly in the nw Caribbean.  They are predicting a rapidly-strengthening hurricane before it even reaches the gulf.  The Euro, on the other hand, has further-delayed the organization over the last two runs.  It now has the system only slowly pulling the energy together over the next two days and reaching tropical storm status, 30+ mb weaker than the overzealous hurricane models at the Yucatan Channel.

[TPAwx]

16 minutes ago, hawkeye_wx said:

It is likely the very intense hurricane models are organizing the system too quickly in the nw Caribbean.  They are predicting a rapidly-strengthening hurricane before it even reaches the gulf.  The Euro, on the other hand, has further-delayed the organization over the last two runs.  It now has the system only slowly pulling the energy together over the next two days and reaching tropical storm status, 30+ mb weaker than the overzealous hurricane models at the Yucatan Channel.

Most of the ex-Euro solutions leave minimal prep and evac time here and thru the panhandle.  Unlike the typical CV systems that are on the public radar for a week or more..  This one is only starting to get local attention this AM.

[Interstate]

2 hours ago, bdgwx said:

Tomer Burg's super ensemble is focusing a possible landfall in the big bend area of Florida.

I love how it snakes between Cuba and Mexico without any land interaction.

[Seminole]

9 minutes ago, wthrmn654 said:

Concensus 

 

The newer track would effect intensity since the COC would miss the GOM loop current later in the run.  

 

 

[olafminesaw]

The 6z Euro is still quite weak entering the gulf

[nvck]

Correct me if I'm wrong, but if the storm post-landfall does take a looping track like that highlighted in some of the models, wouldn't that lead to some pretty intense inland flooding, especially over S Appalachia and the Ozarks? 

[WxWatcher007]

The NHC in the 8am outlook is telegraphing a PTC designation by 11am to issue watches/warnings for Cuba and Mexico. 

[beanskip]

Pretty tight spread for a storm still in the womb.