Major Hurricane Helene

[Rtd208]

06z intensity guidance. Definitely a trend towards a tamer storm. We'll see if it holds.

[Griizzcoat]

IR showing EYE forming -- not concentric , not yet. But clearly shows Helene is getting ready for some RI.

https://weather.cod.edu/satrad/?parms=meso-meso1-13-200-1-10-1&checked=latlon-map&colorbar=undefined

 

[MarkO]

The drier air (possibly influenced by the western side going over the Yucatan) has prettymuch been eliminated. Very favorable conditions for RI over the next 12-18 hrs. This is going to transform into a buzzsaw on satellite. Cat 5 possible/probable by landfall. Not sure how much fetch it can produce with that fast forward speed. But storm surge will be impressive let alone the winds. I hope people on the west coast of FLA up through the eastern pan handle take this one serious. 

[yoda]

BULLETIN
Hurricane Helene Advisory Number  12
NWS National Hurricane Center Miami FL       AL092024
400 AM CDT Thu Sep 26 2024

...HELENE STRENGTHENING AND EXPECTED TO BRING CATASTROPHIC WINDS
AND STORM SURGE TO THE NORTHEASTERN GULF COAST...
...PREPARATIONS TO PROTECT LIFE AND PROPERTY SHOULD BE RUSHED TO
COMPLETION...


SUMMARY OF 400 AM CDT...0900 UTC...INFORMATION
----------------------------------------------
LOCATION...24.2N 86.2W
ABOUT 350 MI...560 KM SW OF TAMPA FLORIDA
ABOUT 385 MI...625 KM S OF APALACHICOLA FLORIDA
MAXIMUM SUSTAINED WINDS...90 MPH...150 KM/H
PRESENT MOVEMENT...NNE OR 15 DEGREES AT 12 MPH...19 KM/H
MINIMUM CENTRAL PRESSURE...966 MB...28.53 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY:

None.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT:

A Storm Surge Warning is in effect for...
* Mexico Beach eastward and southward to Flamingo
* Tampa Bay
* Charlotte Harbor

A Hurricane Warning is in effect for...
* Anclote River to Mexico Beach

A Hurricane Watch is in effect for...
* Englewood to Anclote River, including Tampa Bay

A Tropical Storm Warning is in effect for...
* Florida Keys, including the Dry Tortugas
* Flamingo to Anclote River, including Tampa Bay
* West of Mexico Beach to the Okaloosa/Walton County Line
* Flamingo northward to Little River Inlet
* Lake Okeechobee
* Cuban provinces of Artemisa, Pinar del Rio, and the Isle of Youth

A Storm Surge Warning means there is a danger of life-threatening
inundation, from rising water moving inland from the coastline,
during the next 36 hours in the indicated locations. For a
depiction of areas at risk, please see the National Weather
Service Storm Surge Watch/Warning Graphic, available at
hurricanes.gov.  This is a life-threatening situation.  Persons
located within these areas should take all necessary actions to
protect life and property from rising water and the potential for
other dangerous conditions.  Promptly follow evacuation and other
instructions from local officials.

A Hurricane Warning means that hurricane conditions are expected
somewhere within the warning area.  A warning is typically issued
36 hours before the anticipated first occurrence of
tropical-storm-force winds, conditions that make outside
preparations difficult or dangerous.  Preparations to protect life
and property should be rushed to completion.

A Tropical Storm Warning means that tropical storm conditions are
expected somewhere within the warning area within the next 36 hours.

A Storm Surge Watch means there is a possibility of life-
threatening inundation, from rising water moving inland from the
coastline, in the indicated locations during the next 48 hours.
For a depiction of areas at risk, please see the National Weather
Service Storm Surge Watch/Warning Graphic, available at
hurricanes.gov.

A Hurricane Watch means that hurricane conditions are possible
within the watch area.  A watch is typically issued 48 hours
before the anticipated first occurrence of tropical-storm-force
winds, conditions that make outside preparations difficult or
dangerous.

For storm information specific to your area in the United
States, including possible inland watches and warnings, please
monitor products issued by your local National Weather Service
forecast office. For storm information specific to your area
outside of the United States, please monitor products issued by
your national meteorological service.


DISCUSSION AND OUTLOOK
----------------------
At 400 AM CDT (0900 UTC), the center of Hurricane Helene was located
near latitude 24.2 North, longitude 86.2 West. Helene is moving
toward the north-northeast near 12 mph (19 km/h). This general 
motion is expected to continued with a significant increase in 
forward speed during the next 24 hours. On the forecast track, 
Helene will move across the eastern Gulf of Mexico today and cross 
the Florida Big Bend coast this evening or early Friday morning.  
After landfall, Helene is expected to turn northwestward and slow 
down over the Tennessee Valley on Friday and Saturday.

Maximum sustained winds have increased to near 90 mph (150 km/h) 
with higher gusts.  Strengthening is forecast, and Helene is 
expected to be a major hurricane when it reaches the Florida Big 
Bend coast this evening.  Weakening is expected after landfall, but 
Helene's fast forward speed will allow strong, damaging winds, 
especially in gusts, to penetrate well inland across the 
southeastern United States, including over the higher terrain of 
the southern Appalachians.

Hurricane-force winds extend outward up to 60 miles (95 km) from the
center and tropical-storm-force winds extend outward up to 345 miles
(555 km). The Key West Naval Air Station recently reported 
sustained winds of 41 mph (66 km/h) and a wind gust of 64 mph   
(103 km/h).

The estimated minimum central pressure based on Air Force Reserve 
Hurricane Hunter aircraft data is 966 mb (28.53 inches).


HAZARDS AFFECTING LAND
----------------------
Key Messages for Helene can be found in the Tropical Cyclone
Discussion under AWIPS header MIATCDAT4 and WMO header WTNT44 KNHC
and on the web at hurricanes.gov/text/MIATCDAT4.shtml

STORM SURGE: The combination of a life-threatening storm surge and
the tide will cause normally dry areas near the coast to be flooded
by rising waters moving inland from the shoreline.  The water could
reach the following heights above ground somewhere in the indicated
areas if the peak surge occurs at the time of high tide...

Carrabelle, FL to Suwannee River, FL...15-20 ft
Apalachicola, FL to Carrabelle, FL...10-15 ft
Suwannee River, FL to Chassahowitzka, FL...10-15 ft
Chassahowitzka, FL to Anclote River, FL...8-12 ft
Indian Pass, FL to Apalachicola, FL...6-10 ft
Anclote River, FL to Middle of Longboat Key, FL...5-8 ft
Tampa Bay...5-8 ft
Middle of Longboat Key, FL to Englewood, FL...4-7 ft
East of Mexico Beach, FL to Indian Pass, FL...3-5 ft
Englewood, FL to Flamingo, FL...3-5 ft
Charlotte Harbor...3-5 ft

For a complete depiction of areas at risk of storm surge inundation,
please see the National Weather Service Peak Storm Surge Graphic,
available at hurricanes.gov/graphics_at4.shtml?peakSurge.

Storm surge could raise water levels by as much as 2 to 4 feet above
normal tide levels in areas of onshore winds along the southern
coast of Pinar del Rio, Cuba, including the Isle of Youth.

WIND: Hurricane conditions are expected within the U.S. hurricane
warning area late today, with tropical storm conditions beginning
this morning.  Tropical storm conditions are spreading across the
Florida Keys at this time, and they are expected to spread
northward across the rest of Florida, Georgia, and South Carolina
through tonight.

Tropical storm conditions are expected over portions of the warning
area in western Cuba during the next few hours.

RAINFALL: Hurricane Helene is expected to produce total rain
accumulations of 4 to 8 inches over western Cuba, the Cayman Islands
and the northeast Yucatan Peninsula, with isolated totals around 12
inches. This rainfall brings a risk of considerable flooding.

Over portions of the Southeastern U.S. into the Southern
Appalachians, Helene is expected to produce total rain accumulations
of 6 to 12 inches with isolated totals around 18 inches. This
rainfall will likely result in catastrophic and potentially
life-threatening flash and urban flooding, along with significant
river flooding. Numerous landslides are expected in steep terrain
across the southern Appalachians.

For a complete depiction of forecast rainfall associated with
Hurricane Helene, please see the National Weather Service Storm
Total Rainfall Graphic, available at
hurricanes.gov/graphics_at4.shtml?rainqpf and the Flash Flood Risk
graphic at hurricanes.gov/graphics_at4.shtml?ero.

TORNADOES: The risk for several tornadoes will gradually increase
today through tonight. The greatest threat is expected from parts of
northern Florida into southeast Georgia, the Midlands and Low
Country of South Carolina, and southern North Carolina.

SURF: Swells generated by Helene will affect the southern coast of
Cuba and the Yucatan Peninsula of Mexico during the next couple of
days.  Swells will spread northward toward the west coast of Florida
and the northeastern Gulf Coast today. These swells are likely to
cause life-threatening surf and rip current conditions.  Please
consult products from your local weather office.


NEXT ADVISORY
-------------
Next intermediate advisory at 700 AM CDT.
Next complete advisory at 1000 AM CDT.

$$
Forecaster Beven

 

[yoda]

Hurricane Helene Discussion Number  12
NWS National Hurricane Center Miami FL       AL092024
400 AM CDT Thu Sep 26 2024

Helene is sending some mixed structural signals this morning.  On
one side, an Air Force Reserve Hurricane Hunter aircraft reports
that the central pressure has fallen to near 966 mb, and satellite 
imagery shows the eye is trying to clear out. On another side, the
aircraft reported concentric eyewalls of 16 and 32 n mi diameter, 
with the maximum flight-level winds, 80 kt at 700 mb, occurring 
about 50 n mi southeast of the center likely in relation to the 
outer eyewall.  Based on the central pressure fall and the 
available data, the initial intensity is increased to 80 kt.

The hurricane is starting its expected turn toward the 
north-northeast, with the initial motion now 015/10. The hurricane 
should accelerate north-northeastward during the next 24 h or so in 
the flow between a ridge over the Atlantic and a deep-layer 
baroclinic trough/cut-off low over the Tennessee Valley.  This 
motion should bring the center of Helene to the coast of the Florida 
Big Bend region Thursday evening or early Friday morning.  After 
landfall, Helene should turn northward and northwestward around the 
northeast and north side of the Tennessee Valley system.  After 48 
h, what is left of Helene should make a cyclonic loop as it merges 
with the baroclinic system.  The latest track guidance has nudged a 
little to the northeast, especially near 36 h, and the portion of 
the new forecast track over Georgia and Tennessee has been moved 
a bit to the east.  

Helene remains in an atmospheric and oceanic environment over the
eastern Gulf of Mexico that is very conducive for strengthening,
with the system forecast to traverse the Loop Current while it
remains in a moist and low-shear environment.  The main restraining
factor on intensification is the current concentric eyewall status.  
All of the intensity guidance continues to forecast strengthening 
until landfall.  Based on this, the new intensity forecast calls 
for Helen to become a major hurricane in about 12 h, and additional 
intensification is expected in the ensuing 6 h period or so before 
landfall.  After landfall, Helene should weaken and undergo 
extratropical transition as it merges with the baroclinic system 
over the Tennessee Valley, and this is expected to be complete by 
about 36 h.  The remnant extratropical low is forecast to dissipate 
after 72 h based on global model forecasts.

Helene is forecast to be a large major hurricane when it reaches the
Big Bend coast of Florida.   As a result, storm surge, wind, and
rainfall impacts will extend well away from the center and outside
the forecast cone, particularly on the east side.  In addition, the
fast forward speed when Helene moves inland will result in a far
inland penetration of strong winds over parts of the southeastern
United States, including strong gusts over higher terrain of the
southern Appalachians.  Indeed, the GFS and ECMWF models suggest
the possibility that the inner wind core may persist until the
center reaches northern Georgia.  A higher-than-normal gust factor
is indicated in the official forecast while Helene is inland.


KEY MESSAGES:

1. A catastrophic and deadly storm surge is likely along portions
of the Florida Big Bend coast, where inundation could reach as high
as 20 feet above ground level, along with destructive waves.  There
is also a danger of life-threatening storm surge along the remainder
of the west coast of the Florida Peninsula.  Residents in those
areas should follow advice given by local officials and evacuate if
told to do so.

2. Potentially catastrophic hurricane-force winds are expected
within the eyewall of Helene when it makes landfall in the Florida
Big Bend region later today.  Preparations to protect life and
property should be completed this morning before tropical
storm conditions arrive.  Damaging and life-threatening
hurricane-force winds, especially in gusts, will penetrate well
inland over portions of northern Florida and southern Georgia later 
today and tonight where Hurricane Warnings are in effect.  Strong 
wind gusts are also likely farther north across portions of
northern Georgia and the Carolinas, particularly over the higher
terrain of the southern Appalachians.

3. Catastrophic and life-threatening flash and urban flooding,
including numerous significant landslides, is expected across
portions of the southern Appalachians through Friday. Considerable
to locally catastrophic flash and urban flooding is likely for
northwestern and northern Florida and the Southeast through Friday.
Widespread significant river flooding and isolated major river
flooding are likely.

4. Tropical storm conditions are expected over portions of western
Cuba within the Tropical Storm Warning area.  Hurricane Helene will
bring heavy rain to portions of the western Caribbean with
potentially significant flooding across western Cuba and the
northeastern Yucatan Peninsula through this morning.


FORECAST POSITIONS AND MAX WINDS

INIT  26/0900Z 24.2N  86.2W   80 KT  90 MPH
 12H  26/1800Z 26.8N  85.2W  100 KT 115 MPH
 24H  27/0600Z 31.6N  84.0W   75 KT  85 MPH...INLAND
 36H  27/1800Z 36.1N  84.9W   30 KT  35 MPH...POST-TROP/EXTRATROP
 48H  28/0600Z 37.0N  87.8W   25 KT  30 MPH...POST-TROP/EXTRATROP
 60H  28/1800Z 36.3N  87.8W   20 KT  25 MPH...POST-TROP/EXTRATROP
 72H  29/0600Z 36.3N  86.7W   20 KT  25 MPH...POST-TROP/EXTRATROP
 96H  30/0600Z...DISSIPATED

$$
Forecaster Beven

[CoastalWx]

Looks like an east shift a bit and weaker by NHC.

[WxWatcher007]

Yeah, it looks like the ERC is finishing up, and this is the best it has looked on satellite yet. That said, we need to see how the winds respond. It looks like they’re gradually coming up, at least at FL, and another center pass is imminent so we’ll see how the pressure trend continues. 

NHC has ticked the exact track a touch east, with the center expected right over Tallahassee now. 

[WxWatcher007]

1 minute ago, CoastalWx said:

Looks like an east shift a bit and weaker by NHC.

They do call for additional strengthening in that 6hr period after reaching 115mph, but it’s unclear what they think the peak will be. Maybe down a bit but if we’re going from 90 to 115 today I’m guessing there’s going to be some intensity nowcasting happening. 

[MattPetrulli]

3 minutes ago, CoastalWx said:

Looks like an east shift a bit and weaker by NHC.

Thought so too, but NHC is still using the catastrophic wind wording which is used for category 4+ only so I think it's just the forecast point.

[OSUmetstud]

85 kt flight level in se quad on current pass. That's the highest yet. 

[WxWatcher007]

Extrapolated center pressure of 963.3mb. On the last pass it was 967.7mb. Awaiting dropsonde for confirmed pressure. 

[dan11295]

Just now, WxWatcher007 said:

Extrapolated center pressure of 963.3mb. On the last pass it was 967.7mb. Awaiting dropsonde for confirmed pressure. 

Also getting cold cloud tops almost surrounding the CDO now. Clearly at least steadily strengthening now.

[CoastalWx]

13 minutes ago, MattPetrulli said:

Thought so too, but NHC is still using the catastrophic wind wording which is used for category 4+ only so I think it's just the forecast point.

I think for the surge itself that wording is definitely needed for a 3. 

[CoastalWx]

Definitely looks better on IR. So she’s starting the process.

[OSUmetstud]

3 minutes ago, CoastalWx said:

I think for the surge itself that wording is definitely needed for a 3. 

They can cover their ass a bit. The 18z weakening makes sense to the current state but it could still hit 4 before landfall 7-8 hours later. 

[WxWatcher007]

965mb with an 11kt wind on the center sonde, so ~964mb. First pass had a 970mb pressure. 
 

Dropsonde in the SE eyewall had 69kt at the surface but for the first time we’re seeing 87kt at 925 and 97kt at 850mb.

[OSUmetstud]

So 2 mb drop in 97 minutes between sondes 

[CoastalWx]

11 minutes ago, OSUmetstud said:

They can cover their ass a bit. The 18z weakening makes sense to the current state but it could still hit 4 before landfall 7-8 hours later. 

Yeah I’m sure they’re probably being careful here. I get it. 

[WxWatcher007]

Latest VDM now shows a closed circular eye at 32nm diameter. 8°C temperature contrast. Last VDM had concentric eyewalls open in the NE with the outer eyewall also at 32nm and a 6° temp contrast.

Would like to see an even more organized eye at the next pass to know these changes have taken root (though it looks like it has). 
 

Edited to add: the western side looks weak but the eastern half is looking robust on both IR and recon.

[dan11295]

Helene has all the ingredients for significant wind impacts far inland. Large wind field, fast forward motion, and potentially intensifying until landfall.

[LongBeachSurfFreak]

7 minutes ago, WxWatcher007 said:

Latest VDM now shows a closed circular eye at 32nm diameter. 8°C temperature contrast. Last VDM had concentric eyewalls open in the NE with the outer eyewall also at 32nm and a 6° temp contrast.

Would like to see an even more organized eye at the next pass to know these changes have taken root (though it looks like it has). 
 

Edited to add: the western side looks weak but the eastern half is looking robust on both IR and recon.

Not surprising given forward speed and interaction with synoptic environment . This was clearly modeled as well. I think that’s why this never goes full on cat 5. Se quadrant is going to be a prolific surge producer. 

[Kevin Reilly]

24 minutes ago, LongBeachSurfFreak said:

Not surprising given forward speed and interaction with synoptic environment . This was clearly modeled as well. I think that’s why this never goes full on cat 5. Se quadrant is going to be a prolific surge producer. 

Yes, a prolific surge producer on the Southeast side and east side all the way to the coast in some cases pretty devastating.

[beanskip]

If you want to have a little fun, plot the lat/long of the lowest pressure reading from this recon run on to the 2 am NHC track. 
 

Also, 6z hurricane models running. HAFS-B 13 mb higher than last run through just 9 hours. 

[WxWatcher007]

Eyewall starting to show up on Key West radar. 

[dan11295]

7 minutes ago, beanskip said:

If you want to have a little fun, plot the lat/long of the lowest pressure reading from this recon run on to the 2 am NHC track. 
 

Also, 6z hurricane models running. HAFS-B 13 mb higher than last run through just 9 hours. 

The HAFS has been too aggressive with intensification of Helene in general so maybe getting a bit closer to reality.

[NorthHillsWx]

Flight level winds way up this pass, over 100 kts

[WxWatcher007]

There are two recon missions ongoing now, and one that is making an east to west pass is reporting FL winds between 99-104kt. Intensification is still going.

[OSUmetstud]

The noaa3 plan recon is at 750mb not 700mb but it I think it still supports about 90 kt surface. 

[BoulderWX]

Glad to see this didn’t explode overnight but seems like it’s getting its act together this AM. prayers and best wishes for all in its path. Will be a fascinating day of tracking. 

[WxWatcher007]