Tropical Storm Helene Discussion Number   8
NWS National Hurricane Center Miami FL       AL092024
400 AM CDT Wed Sep 25 2024

Helen has strengthened some since the last advisory.  Reports from 
an Air Force Reserve Hurricane Hunter aircraft indicate that 
the central pressure has fallen to 985 mb, and that the maximum 
850 mb flight-level were 58 kt in the northeastern quadrant. A 
dropsonde in the northwest quadrant reported a splash wind of 59 
kt, but the boundary-layer average suggested sustained winds closer 
to 45 kt.  Based on these data and increasing satellite intensity 
estimates, the initial intensity is increased to 55 kt.  Despite 
the increased intensity, the aircraft data, along with radar data 
from Mexico and Cuba, show that Helen has not yet formed a 
well-defined inner core.

The initial motion is 325/8 kt.  Helen should turn northward during 
the next 12 h or so on the western side of a mid-level ridge, and 
then it should accelerate northward to north-northeastward as it 
become embedded in the deep-layer flow between the ridge and a 
mid-latitude trough/developing cut-off low over the Mississippi 
valley.  This motion should bring the center near the northeastern 
coast of the Yucatan Peninsula this morning, then across the 
eastern Gulf of Mexico tonight and Thursday to a landfall along the 
northeast coast of the Gulf of Mexico late Thursday or Thursday 
night.  After landfall, Helene should curve cyclonically around the 
cut-off low until it dissipates.  The new forecast track is little 
changed from the previous track.

Over the next couple of days, Helene will be moving through an
environment of low vertical wind shear, ample environmental
moisture, and over waters of high oceanic heat content.  All 
guidance forecasts steady to rapid intensification, including the 
RI indices associated with the SHIPS model.  The latest forecast 
calls for a 105 kt intensity by 36 h, and this could be 
conservative as some of the guidance is stronger.  After landfall, 
Helen is forecast to weaken and become post-tropical as it gets 
tangled up in the baroclinic system over the southeastern United 
States.

Helene's wind field is predicted to grow to a very large size in the 
NHC forecast.  Therefore storm surge, wind, and rainfall impacts 
will likely extend well away from the center and outside the 
forecast cone, particularly on the east side.  In addition, the fast 
forward speed while Helene crosses the coast will likely result in 
farther inland penetration of strong winds over parts of the 
southeastern United States after landfall.


KEY MESSAGES:

1. Helene is forecast to intensify and be near hurricane strength
when it passes near the northeastern coast of the Yucatan
Peninsula during the next several hours, where a Hurricane Warning 
is in effect.

2. Helene is expected to rapidly intensify and grow in size over the
eastern Gulf of Mexico.  There is a danger of life-threatening storm
surge along the entire west coast of the Florida Peninsula and
Florida Big Bend.  The highest inundation levels are expected along 
the coast of the Florida Big Bend.  Residents in those areas should 
follow advice given by local officials and evacuate if told to do 
so.

3. Damaging hurricane-force winds are expected along portions of
coast of the Florida Big Bend, where a Hurricane Warning is now in
effect.  Preparations to protect life and property should be
completed by early Thursday since tropical storm conditions are
expected to begin within this area on Thursday.

4. Tropical Storm Helene will bring heavy rain to portions of the 
western Caribbean with potentially significant flooding across 
western Cuba and the northeastern Yucatan Peninsula. Considerable 
and potentially life-threatening flash and urban flooding is 
expected across portions of Florida, the Southeast, the Southern 
Appalachians, and the Tennessee Valley beginning today through 
Friday. This includes the risk of landslides across the southern 
Appalachians. Widespread minor to moderate river flooding is likely, 
and isolated major river flooding is possible.


FORECAST POSITIONS AND MAX WINDS

INIT  25/0900Z 20.7N  86.2W   55 KT  65 MPH
12H  25/1800Z 21.9N  86.5W   70 KT  80 MPH
24H  26/0600Z 24.1N  86.2W   90 KT 105 MPH
36H  26/1800Z 27.4N  85.0W  105 KT 120 MPH
48H  27/0600Z 32.0N  84.2W   65 KT  75 MPH...INLAND
60H  27/1800Z 35.9N  85.4W   30 KT  35 MPH...POST-TROP/INLAND
72H  28/0600Z 37.0N  87.8W   20 KT  25 MPH...POST-TROP/INLAND
96H  29/0600Z 36.5N  88.0W   20 KT  25 MPH...POST-TROP/INLAND
120H  30/0600Z...DISSIPATED

$$
Forecaster Beven