Hurricane Helene Forecast Discussion

000
WTNT44 KNHC 260255
TCDAT4

Hurricane Helene Discussion Number  11
NWS National Hurricane Center Miami FL       AL092024
1000 PM CDT Wed Sep 25 2024

Satellite images show that Helene has a well-organized appearance, 
with numerous convective banding features.  A ragged-looking eye 
feature is also apparent.  However, reports from both Air Force and 
a NOAA Hurricane Hunter aircraft investigating the system suggest 
that the it lacks a well-defined inner core with a somewhat broad 
maximum wind field for now.  The central pressure has dropped a 
little to around 972 mb.  Given the slowly falling central 
pressure, the intensity is maintained at 75 kt for this advisory.  
Helene's structure and intensity will continue to be closely 
monitored by Hurricane Hunter aircraft tonight and Thursday.

The hurricane continues moving northward with an estimated initial
motion of 360/08 kt.  For the next couple of days, the steering
scenario for this system remains basically unchanged from the
earlier advisory.  The flow between a mid-tropospheric trough over
the east-central United States and a ridge over the western
Atlantic should result in Helene accelerating northward to
north-northeastward during the next 24 to 36 hours. This motion 
will bring the center of Helene to the northeastern Gulf of Mexico 
coast in about 24 hours.  The official track forecast through 
landfall is very similar to the previous NHC prediction and remains 
close to the corrected consensus guidance. After landfall, the 
trough to the northwest of the tropical cyclone becomes a cutoff 
low, and Helene should turn leftward as it rotates around the low.  
In 3-4 days, the system should become a shallow extratropical 
cyclone within weaker steering currents.

Helene should be in an atmospheric and oceanic environment over the
eastern Gulf of Mexico that will be very conducive for 
strengthening.  The system is expected to traverse the Loop Current, 
which has especially high oceanic heat content.  This, along with 
fairly low vertical wind shear and a moist mid- to lower- 
tropospheric air mass, should likely result in rapid 
intensification before landfall.  The official forecast continues
to call for the hurricane to reach category 4 status tomorrow.  It 
should be noted that the HAFS-A and HAFS-B regional hurricane models 
show even more intensification than indicated here.

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.  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 late Thursday.  Preparations to protect life and
property should be completed by early Thursday 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 late
Thursday and Thursday night 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 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 minor 
to moderate 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 into early Thursday.


FORECAST POSITIONS AND MAX WINDS

INIT  26/0300Z 23.1N  86.6W   75 KT  85 MPH
 12H  26/1200Z 25.4N  86.1W   95 KT 110 MPH
 24H  27/0000Z 29.5N  84.5W  115 KT 130 MPH
 36H  27/1200Z 34.3N  84.7W   50 KT  60 MPH...INLAND
 48H  28/0000Z 36.7N  87.1W   30 KT  35 MPH...POST-TROP/EXTRATROP
 60H  28/1200Z 36.8N  88.5W   25 KT  30 MPH...POST-TROP/EXTRATROP
 72H  29/0000Z 36.7N  87.0W   20 KT  25 MPH...POST-TROP/EXTRATROP
 96H  30/0000Z 36.7N  84.9W   15 KT  15 MPH...POST-TROP/EXTRATROP
120H  01/0000Z...DISSIPATED

$$
Forecaster Pasch