Major Hurricane Helene

[wncsnow]

12Z ICON is about 15 mb lower than 6Z at landfall

[GaWx]

Tropical Storm Helene Discussion Number   5
NWS National Hurricane Center Miami FL       AL092024
1100 AM EDT Tue Sep 24 2024

An Air Force Reserve Hurricane Hunter measured peak 925-mb
flight-level winds of 52 kt to the northeast of the center, which
supports an initial intensity of 40 kt.  Dropsonde data also
indicated that the central pressure is down to 1000 mb. Very 
recently, data from the plane and one-minute visible satellite 
imagery indicate that the center has become better defined. Based 
on these data, the system is being designated as Tropical Storm 
Helene at this time.

Helene is moving a little faster toward the northwest (310/10 kt) 
as it moves around a mid-level area of high pressure located over 
Florida and the Southeastern U.S.  The high is expected to slide 
eastward through Wednesday as a deep-layer trough digs southward 
over the Lower Mississippi Valley.  This pattern evolution should 
cause the system to turn northward and north-northeastward late 
Wednesday into Thursday.  The track guidance is very tightly 
clustered, which would normally imply high forecast confidence.  
However, depending on exactly where the center forms could end up 
shifting the entire guidance suite in future cycles, so it is 
imperative to not focus on specific landfall locations this far in 
the future.

Satellite trends suggest that the shear over the system is
beginning to decrease, and model guidance continues to show
relatively low to moderate shear for the next 48 hours or so.  In
addition, oceanic heat content values are very high, and the system
will be moving through an environment of upper-level divergence.
Therefore, significant strengthening is anticipated, and the NHC
intensity forecast shows the system reaching a peak intensity
around 100 kt in 48 hours while over the eastern Gulf of Mexico.
There could be some increase in shear around the time the system
reaches the coast, given the system's large size, it might only
weaken slowly.  As a result, there is still a risk that the system
could reach the coast as a major hurricane.

Helene's forecast radii are at the 90th percentile of hurricane
size at similar latitudes.  Due to the forecast large size of this
system, storm surge, wind, and rainfall impacts will extend well
away from the center, particularly on the east side.  In addition,
the fast forward speed while it crosses the coast will likely result
in farther inland penetration of strong winds over parts of the
southeastern United States after landfall.

FORECAST POSITIONS AND MAX WINDS

INIT  24/1500Z 19.5N  84.3W   40 KT  45 MPH
 12H  25/0000Z 20.3N  85.2W   50 KT  60 MPH
 24H  25/1200Z 21.5N  86.3W   65 KT  75 MPH
 36H  26/0000Z 23.2N  86.3W   80 KT  90 MPH
 48H  26/1200Z 25.9N  85.4W  100 KT 115 MPH
 60H  27/0000Z 29.7N  84.3W  100 KT 115 MPH
 72H  27/1200Z 33.9N  83.9W   45 KT  50 MPH...INLAND
 96H  28/1200Z 39.7N  86.8W   20 KT  25 MPH...POST-TROPICAL
120H  29/1200Z...DISSIPATED

$$
Forecaster Berg

[WxWatcher007]

4 minutes ago, Hotair said:

Helene is born. Will there be a new thread ? Or rename this one ?

The thread gets renamed, and I try to keep the latest advisory info in the title until landfall. 

[Seminole]

17 minutes ago, purduewx80 said:

Is that shear in the room with us? This is an ideal setup for ventilation and expansive outflow in at least three quadrants. 

Yep! Misread the 27th for 26th so I was wrong. 

 

[wxeyeNH]

What am I missing?  As of 11:15 eastern time the LLC seems to becoming more exposed and moving to the SSW.  That doesn't seem to indicate immediate strenghtening.  https://weather.cod.edu/satrad/?parms=meso-meso1-truecolor-48-1-100-1&checked=map&colorbar=undefined

[MANDA]

Interesting Satellite loop (time sensitive) as center continues to drift sw away from deepest convection.

No doubt there are TS winds associated with all the convection to the NE of the LLC so I get the upgrade.

Will be interesting to see if convection develops over current LLC or new enter forms under the deep convection.

ULL over the Yucatan is backing NW but there is clearly still SW shear affecting Helene.  Interesting to watch this develop.

I would not be surprised to see nudges east in the track over the next 24 hours or so.  Either way depending on how fast Helene can intensify the current track (depending on intensity) could push A LOT of water onto the west coast of FL, especially from just south of Tampa northward.

 

Link to visible loop:

https://www.meteo.psu.edu/ewall/PSUGOES_MESO1/loop60.html

[CoastalWx]

@wxeyeNH I noticed that too. It's occurring after the early posts about alignment. We could see a new center develop closer to the convection..but IMO things aren't close to taking off quite yet.

[schoeppeya]

13 minutes ago, CoastalWx said:

@wxeyeNH I noticed that too. It's occurring after the early posts about alignment. We could see a new center develop closer to the convection..but IMO things aren't close to taking off quite yet.

Yeah what a mess

[hawkeye_wx]

The 12z GFS shows several little pieces of vorticity pinwheeling around each other for the next couple days, which keeps Helene weak.  It may be too weak.

[hooralph]

Charlotte Country (Port Charlotte) has already ordered evacuations. Overreaction? Proper reaction?

[GaWx]

12Z GFS: landfall near 975 (weaker than recent runs) Big Bend Thu evening

[Wormy2005]

@hooralphI think it's a proper reaction, its better to be safe than sorry!! 

[TPAwx]

3 minutes ago, hooralph said:

Charlotte Country (Port Charlotte) has already ordered evacuations. Overreaction? Proper reaction?

Proactive and appropriate IMO for a coastal/low lying county and area.  Not in the current cone but as others as noted Helene will push a significant surge along the FL West Coast.

[smokeybandit]

6 minutes ago, hooralph said:

Charlotte Country (Port Charlotte) has already ordered evacuations. Overreaction? Proper reaction?

Their emergency management website only shows they're in the "monitoring" stage.

https://www.charlottecountyfl.gov/departments/public-safety/emergency-management/

[JP11283]

22 minutes ago, hooralph said:

Charlotte Country (Port Charlotte) has already ordered evacuations. Overreaction? Proper reaction?

Their Facebook page includes homes that don’t meet 1995 building codes in the order. Seems excessive to me, that's a lot of homes, and there's quite a bit of confusion in the comments.

[TPAwx]

Wouldn't be surprised to see most segments hit or exceed these levels

[cptcatz]

Last few frames of visible satelite make it look like that naked swirl is moving almost due south.  

[Hotair]

24 minutes ago, hooralph said:

Charlotte Country (Port Charlotte) has already ordered evacuations. Overreaction? Proper reaction?

Very appropriate considering the unknowns and the certainty that this event will happen mid week without the luxury for most to prepare over a weekend.

[GaWx]

12Z CMC: 977 Big Bend Thu night, but it only weakens to 978 mb SE of Atlanta! That would be bordering on alltime record low SLPs in that region of GA. The potential damage well inland should not be understated.

[jbenedet]

You can see a PRE setup pretty clearly on the major guidance, but it’s obvious on the 12z CMC. Most guidance currently centered around Tallahassee for the best forcing. 

[jbenedet]

10 minutes ago, GaWx said:

12Z CMC: 977 Big Bend Thu night, but it only weakens to 978 mb SE of Atlanta! That would be bordering on alltime record low SLPs in that region of GA. The potential damage well inland should not be understated.

Significant -NAO patterns are good for displacing climatological patterns. This syntopic interaction and extra tropical transition is common to what is experienced in the northeast; unusual in the southeast…

[wncsnow]

The inland flooding could be devastating with the PRE and Helene combo. Southern Appalachian areas could see as much impact as Florida with flash flooding, mud slides, and high winds in the higher elevations. Some areas along the Blue Ridge could easily see 12-16" of rain with orographic uplift with the SE flow

[StantonParkHoya]

12 minutes ago, GaWx said:

12Z CMC: 977 Big Bend Thu night, but it only weakens to 978 mb SE of Atlanta! That would be bordering on alltime record low SLPs in that region of GA. The potential damage well inland should not be understated.

Yeah, call me skeptical. Never seen a TC that didn’t begin weakening rapidly upon LF.

[TPAwx]

Can’t get tweets to embed properly, but Andy Hazelton saying the 12z hurricane models will have TDR/Tail Doppler Radar ingested and should be more realistic with outputs.

[GaWx]

4 minutes ago, jbenedet said:

Significant -NAO patterns are good for displacing climatological patterns. This syntopic interaction and extra tropical transition is common to what is experienced in the northeast; unusual in the southeast…

And currently the -NAO is by far the strongest on record for September at below -2.7! The -NAO peak is today and tomorrow.

[GaWx]

12Z UKMET: E shift and a bit stronger vs 0Z bringing it into Apalachee Bay (instead of near Apalachicola) Thu night; goes to a little E of ATL vs near ATL on 0Z

TROPICAL STORM 09L        ANALYSED POSITION : 19.5N  83.5W

     ATCF IDENTIFIER : AL092024

                        LEAD                 CENTRAL     MAXIMUM WIND
      VERIFYING TIME    TIME   POSITION   PRESSURE (MB)  SPEED (KNOTS)
      --------------    ----   --------   -------------  -------------
    1200UTC 24.09.2024    0  19.5N  83.5W     1003            37
    0000UTC 25.09.2024   12  20.0N  85.3W      998            37
    1200UTC 25.09.2024   24  21.1N  86.0W      993            40
    0000UTC 26.09.2024   36  22.5N  86.3W      989            40
    1200UTC 26.09.2024   48  24.7N  85.5W      987            48
    0000UTC 27.09.2024   60  28.4N  84.4W      983            51
    1200UTC 27.09.2024   72  33.3N  83.3W      986            41
    0000UTC 28.09.2024   84  38.1N  84.1W      995            31
    1200UTC 28.09.2024   96  37.5N  90.7W     1000            17
    0000UTC 29.09.2024  108  36.4N  91.4W     1003            13
    1200UTC 29.09.2024  120  35.3N  92.4W     1007            12
    0000UTC 30.09.2024  132              CEASED TRACKING

 

[SnowGoose69]

6 minutes ago, StantonParkHoya said:

Yeah, call me skeptical. Never seen a TC that didn’t begin weakening rapidly upon LF.

Even Hugo moving at 25 was a 75-80 mph storm when it got to Charlotte so yeah, likely just a strong TS by the time it got to like ATL or near there but thats still bad with saturated ground.

[NorthHillsWx]

I am confused with the systems organization today. That naked swirl is definitely the COC recon found but there is no reason why is should be going south. It doesn’t appear to be part of a larger cyclonic gyre but I guess that is the only explanation 

[Normandy]

2 minutes ago, NorthHillsWx said:

I am confused with the systems organization today. That naked swirl is definitely the COC recon found but there is no reason why is should be going south. It doesn’t appear to be part of a larger cyclonic gyre but I guess that is the only explanation 

Both things can be true:  that is the COC and it’s still embedded within the larger gyre.  I think this will stall for a bit then start creeping north before again turning wnw later today

[Radtechwxman]

What a mess. Lol. LLC running away from convection. Shear definitely still impacting Helene. I'm beginning to think it may not get its act together until the Gulf.