Hurricane Helene Discussion Number 14
NWS National Hurricane Center Miami FL AL092024
500 PM EDT Thu Sep 26 2024

Helene has rapidly intensified today while nearing landfall in the
Florida Big Bend. Doppler radar and aircraft data indicate that the
eyewall is now completely closed and the eye has become more
circular and is clearing out. The aircraft data also indicated
that the inner core has contracted significantly today while the
tropical-storm-force winds have expanded. Based on all of the data,
the initial intensity is set at 110 kt. The latest minimum pressure
based on the aircraft data is around 951 mb. Tropical-storm-force
winds are occurring across portions of west-central and southwestern
Florida, and conditions are expected to deteriorate rapidly in the
hurricane warning area during the next several hours. It should be
emphasized that Helene is at the upper bound of hurricanes in
terms of storm size and impacts are and will occur well away
from the center.

The large hurricane is now accelerating north-northeastward, with
the latest initial motion estimated to be 025/20 kt. This general
motion is expected to continue, taking the core of the major
hurricane to the Florida Big Bend later this evening. After
landfall, a turn to the north over Georgia is expected late tonight
and early Friday, followed by a slowdown or a complete stall over
the Tennessee Valley late Friday and Saturday when Helene merges
with a mid- to upper-level low.

The hurricane has intensified by 30 kt since sunrise and given the
conducive environmental conditions and contracting inner core, it
seems likely that Helene will be at or very near category 4 strength
when it makes landfall in the Florida Big Bend this evening.
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 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 will occur along portions
of the Florida Big Bend coast, where inundation could reach as high
as 20 feet above ground level, along with destructive waves. If
you live in this area and were told to evacuate by local officials,
your opportunity to do so is almost over. There is also a danger
of life-threatening storm surge along the remainder of the west
coast of the Florida Peninsula.

2. Potentially catastrophic hurricane-force winds are expected
within the eyewall of Helene and will spread inland over portions
of northern Florida and southern Georgia when Helene makes landfall
in the Florida Big Bend region this evening. Persons in these
areas should be prepared to take shelter in the interior portion of
a well-built structure and remain sheltered until after hazardous
conditions pass. You may need to remain sheltered after the storm
due to downed trees and power lines, as well as flooding, in the
area.

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 26/2100Z 27.9N 84.6W 110 KT 125 MPH
12H 27/0600Z 31.5N 83.7W 90 KT 105 MPH...INLAND
24H 27/1800Z 35.8N 85.0W 40 KT 45 MPH...POST-TROP/EXTRATROP
36H 28/0600Z 37.0N 86.5W 30 KT 35 MPH...POST-TROP/EXTRATROP
48H 28/1800Z 37.1N 87.0W 25 KT 30 MPH...POST-TROP/EXTRATROP
60H 29/0600Z 37.1N 87.3W 20 KT 25 MPH...POST-TROP/EXTRATROP
72H 29/1800Z...DISSIPATED

$$
Forecaster Cangialosi

BULLETIN
Hurricane Helene Advisory Number 14
NWS National Hurricane Center Miami FL AL092024
500 PM EDT Thu Sep 26 2024

...HELENE IS A VERY DANGEROUS AND LARGE MAJOR HURRICANE...
...DAMAGING HURRICANE WINDS AND CATASTROPHIC STORM SURGE
EXPECTED TO BEGIN IN THE FLORIDA BIG BEND THIS EVENING...


SUMMARY OF 500 PM EDT...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...27.9N 84.6W
ABOUT 130 MI...205 KM W OF TAMPA FLORIDA
ABOUT 175 MI...280 KM S OF TALLAHASSEE FLORIDA
MAXIMUM SUSTAINED WINDS...125 MPH...205 KM/H
PRESENT MOVEMENT...NNE OR 25 DEGREES AT 23 MPH...37 KM/H
MINIMUM CENTRAL PRESSURE...951 MB...28.09 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. 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.

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 500 PM EDT (2100 UTC), the eye of Hurricane Helene was located
near latitude 27.9 North, longitude 84.6 West. Helene is moving
toward the north-northeast near 23 mph (37 km/h). A continued fast
motion to the north-northeast is expected through landfall in the
Florida Big Bend this evening. 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 125 mph (205 km/h)
with higher gusts. Helene is a category 3 hurricane on the
Saffir-Simpson Hurricane Wind Scale. Additional strengthening is
expected, and Helene will likely be an extremely dangerous category
4 hurricane at landfall. 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 weather station at Venice Municipal Airport recently
reported a sustained wind of 46 mph (74 km/h) with a gust of 69 mph
(111 km/h). Another observation near Venice Beach reported a
sustained wind of 51 mph (82 km/h) with a gust to 66 mph (106
km/h).

The estimated minimum central pressure based on data from the Air
Force Hurricane Hunters is 951 mb (28.09 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

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 expected within the hurricane warning
area this evening. Tropical storm conditions are occurring in the
southern and central Florida, and these conditions are expected to
spread 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 through
tonight over much of Florida, southeast Georgia, central and
southern South Carolina, and southern North Carolina. The tornado
risk will continue 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 800 PM EDT.
Next complete advisory at 1100 PM EDT.

$$
Forecaster Cangialosi