Hurricane Helene Discussion Number 15
NWS National Hurricane Center Miami FL AL092024
1100 PM EDT Thu Sep 26 2024

The hurricane is about to make landfall in the Florida Big Bend
region. Timely observations from Air Force and NOAA Hurricane
Hunter aircraft showed that Helene continued to strengthen rapidly
to Category 4 status before it approached the coast, with the
central pressure falling at about 3 mb per hour since this
afternoon. Peak 700 mb flight-level winds from the aircraft were
136 kt, corresponding to an intensity of about 120 kt, which might
be a bit conservative. Radar and satellite images show numerous
mesocyclones rotating around the eyewall.

The large hurricane continues moving rapidly north-northeastward
with the latest initial motion estimated to be 015/21 kt. A
generally northward track is expected overnight, taking the center
from southern to northern Georgia through early Friday morning.
Later on Friday and Saturday, Helene should slow down considerably
while it interacts with a mid-level low to its northwest and west.
The weakening system is likely to become nearly stationary in 48-60
hours. The official track forecast follows the dynamical model
consensus.

Although the system will weaken as it moves over land, the fast
forward speed of Helene during the next 12 hours or so will result
in a far inland penetration of strong winds over parts of the
southeastern United States, particularly over Georgia, including
strong gusts over the higher terrain of the southern Appalachians.
Accordingly, 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 occurring 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.

2. Catastrophic hurricane-force winds are occurring near the coast
within the eyewall of Helene and will spread inland over portions
of northern Florida and southern Georgia.

3. Damaging wind gusts will penetrate well inland over portions of
Georgia and the Carolinas tonight, particularly over the higher
terrain of the southern Appalachians. Residents in these areas
should be prepared for the possibility of long-duration power
outages. If you use a generator after the storm, be sure it is
placed outside at least 20 feet away from doors, windows, and
garages to avoid deadly carbon monoxide poisoning.

4. 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.


FORECAST POSITIONS AND MAX WINDS

INIT 27/0300Z 29.9N 83.9W 120 KT 140 MPH
12H 27/1200Z 33.9N 84.0W 55 KT 65 MPH...INLAND
24H 28/0000Z 36.9N 86.2W 30 KT 35 MPH...POST-TROP/EXTRATROP
36H 28/1200Z 36.8N 87.5W 25 KT 30 MPH...POST-TROP/EXTRATROP
48H 29/0000Z 36.9N 86.9W 20 KT 25 MPH...POST-TROP/EXTRATROP
60H 29/1200Z 37.1N 86.4W 20 KT 25 MPH...POST-TROP/EXTRATROP
72H 30/0000Z...DISSIPATED

$$
Forecaster Pasch

BULLETIN
Hurricane Helene Advisory Number 15
NWS National Hurricane Center Miami FL AL092024
1100 PM EDT Thu Sep 26 2024

...HURRICANE HELENE VERY CLOSE TO MAKING LANDFALL IN THE FLORIDA BIG
BEND...
...ACCOMPANIED BY A CATASTROPHIC STORM SURGE AND LIFE-THREATENING
WINDS...


SUMMARY OF 1100 PM EDT...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...29.9N 83.9W
ABOUT 75 MI...120 KM NW OF CEDAR KEY FLORIDA
ABOUT 40 MI...70 KM SE OF TALLAHASSEE FLORIDA
MAXIMUM SUSTAINED WINDS...140 MPH...220 KM/H
PRESENT MOVEMENT...NNE OR 15 DEGREES AT 24 MPH...39 KM/H
MINIMUM CENTRAL PRESSURE...938 MB...27.70 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

A Storm Surge Warning means there is a danger of life-threatening
inundation, from rising water moving inland from the coastline. 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 Tropical Storm Warning means that tropical storm conditions are
expected somewhere within the warning area.

A Hurricane Watch means that hurricane conditions are possible
within the watch area.

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 1100 PM EDT (0300 UTC), the center of Hurricane Helene was
located near latitude 29.9 North, longitude 83.9 West. Helene is
moving toward the north-northeast near 24 mph (39 km/h). A turn
toward the north is expected overnight, taking the center over
Georgia. The center of the hurricane should make landfall
very soon in the Big Bend region of Florida. After landfall,
Helene is expected to turn northwestward and slow down over the
Tennessee Valley on Friday and Saturday.

Maximum sustained winds are near 140 mph (220 km/h) with higher
gusts. Helene is an extremely dangerous category 4 hurricane on
the Saffir-Simpson Hurricane Wind Scale. Weakening is expected
after Helene moves inland, but the 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 310 miles
(500 km). A sustained wind of 64 mph (103 km/h) with a gust to 84
mph (135 km/h) was recently reported at Cedar Key, Florida. A
gust of 83 mph (134 km/h) was recently reported at Steinhatchee,
Florida.

The estimated minimum central pressure based on Hurricane Hunter
aircraft observations is 938 mb (27.70 inches).

A NOAA National Ocean Service tide gauge located on Cedar Key
recently reported a water level of 7.33 feet above mean higher high
water.


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

The deepest water will occur along the immediate coast near and to
the east of the landfall location, where the surge will be
accompanied by large and dangerous waves. Surge-related flooding
depends on the relative timing of the surge and the tidal cycle,
and can vary greatly over short distances. For information
specific to your area, please see products issued by your local
National Weather Service forecast office.

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.

WIND: Hurricane conditions are occurring within the hurricane
warning area. When the eye passes over, people are reminded to not
venture out into the relative calm, as hazardous winds will increase
very quickly when the eye passes. Tropical storm conditions are
occurring in southern and central Florida, and these conditions will
continue spreading northward across the tropical storm warning
areas in the Southeastern U.S. through early Friday. Strong,
damaging winds, especially in gusts, will likely penetrate as far
inland as the higher terrain of the southern Appalachians.

RAINFALL: 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 20 inches. This
rainfall will likely result in catastrophic and potentially
life-threatening flash and urban flooding, along with significant
river flooding. Numerous significant 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.

For a list of rainfall observations (and wind reports) associated
this storm, see the companion storm summary at WBCSCCNS4 with the
WMO header ACUS44 KWBC or at the following link:
www.wpc.ncep.noaa.gov/discussions/nfdscc4.html.

TORNADOES: The risk for several tornadoes continues tonight through
early Friday morning over parts of north/central Florida, Georgia,
South Carolina, and southern North Carolina. The tornado risk will
persist Friday across the Carolinas and southern Virginia.

SURF: Swells generated by Helene will affect much of Florida and
the coasts of Georgia and the Carolinas during the next couple of
days. 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 200 AM EDT.
Next complete advisory at 500 AM EDT.

$$
Forecaster Pasch