Hurricane Helene Discussion Number 13
NWS National Hurricane Center Miami FL AL092024
1000 AM CDT Thu Sep 26 2024

Helene is gaining strength as it approaches the Florida Big Bend. A
large eye has become apparent in satellite images, and that feature
has been gradually clearing out over the past few hours. Convective
banding is wrapping around the eye, and recent microwave images and
reports from the NOAA and Air Force Hurricane Hunter aircraft
indicate than an eyewall is almost completely closed. The minimum
pressure has been dropping steadily to near 960 mb, and based on the
aircraft flight-level wind data, the initial intensity is estimated
to have increased to 90 kt. There have been several reports of
tropical-storm-force winds occurring in portions of South Florida
and the Florida Keys during the past few hours.

The large hurricane is picking up speed and has turned slightly to
the north-northeast. The latest initial motion is 025/12 kt. A
notably faster north-northeastward motion is expected through
landfall, which is expected to occur in the Florida Big Bend region
this evening. After Helene moves inland, it is forecast to track
over Georgia and then slow down or stall over the Tennessee Valley
when it merges with a mid- to upper-level low pressure system. Only
minor changes were made to the previous NHC track forecast.

Significant intensification is expected until Helene reaches the
coast since the overall atmospheric and oceanic conditions will
remain conducive. The amount of strengthening will likely depend on
how much the inner core can contract and consolidate. The HWRF and
HMON models show significant strengthening to category 4 status,
while most of the other models are a little lower. The main message
is that Helene will likely make landfall as a large major hurricane
in the Florida Big Bend this evening, and all preparations in the
hurricane warning area should be rushed to completion.

It should also be re-emphasized that Helene is a very large
hurricane. In fact, comparing the system with previous hurricanes
in the Gulf of Mexico over the past couple of decades, Helene is at
the upper bound in terms of size. As a result, storm surge, wind,
and rainfall impacts will extend far away from the center and well
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. 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 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 this evening. Preparations to protect life and
property should be rushed to completion. 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.


FORECAST POSITIONS AND MAX WINDS

INIT 26/1500Z 25.5N 85.5W 90 KT 105 MPH
12H 27/0000Z 28.8N 84.3W 105 KT 120 MPH
24H 27/1200Z 33.9N 84.5W 55 KT 65 MPH...INLAND
36H 28/0000Z 36.4N 86.6W 30 KT 35 MPH...POST-TROP/EXTRATROP
48H 28/1200Z 36.5N 87.5W 25 KT 30 MPH...POST-TROP/EXTRATROP
60H 29/0000Z 36.3N 87.6W 20 KT 25 MPH...POST-TROP/EXTRATROP
72H 29/1200Z 36.2N 87.2W 20 KT 25 MPH...POST-TROP/EXTRATROP
96H 30/1200Z...DISSIPATED

$$
Forecaster Cangialosi

BULLETIN
Hurricane Helene Advisory Number 13
NWS National Hurricane Center Miami FL AL092024
1000 AM CDT Thu Sep 26 2024

...HELENE STRENGTHENING AND EXPECTED TO MAKE LANDFALL IN THE
FLORIDA BIG BEND THIS EVENING AS A MAJOR HURRICANE...
...PREPARATIONS TO PROTECT LIFE AND PROPERTY SHOULD BE RUSHED TO
COMPLETION...


SUMMARY OF 1000 AM CDT...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...25.5N 85.5W
ABOUT 255 MI...405 KM SW OF TAMPA FLORIDA
ABOUT 290 MI...470 KM S OF APALACHICOLA FLORIDA
MAXIMUM SUSTAINED WINDS...105 MPH...165 KM/H
PRESENT MOVEMENT...NNE OR 25 DEGREES AT 14 MPH...22 KM/H
MINIMUM CENTRAL PRESSURE...960 MB...28.35 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. 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 1000 AM CDT (1500 UTC), the center of Hurricane Helene was
located near latitude 25.5 North, longitude 85.5 West. Helene is
moving toward the north-northeast near 14 mph (22 km/h). A
significant increase in forward speed is expected during the next 24
hours. On the forecast track, Helene will make landfall in the
Florida Big Bend region 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 105 mph (165 km/h)
with higher gusts. Additional 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.

Helene is a very large hurricane. 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 minimum central pressure based on data from the Air Force
Hurricane Hunters is 960 mb (28.35 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 U.S. hurricane
warning area late today. Tropical storm conditions have
already begun in the Florida Keys and portions of south
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.

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

RAINFALL: Hurricane Helene is expected to produce total rain
accumulations of 4 to 8 inches over western Cuba. 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 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 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 much of Florida and
the coasts of Georgia and the Carolinas during the next couple of
days. Swells will also continue across portions of Cuba and the
Yucatan Peninsula through tonight. 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 100 PM CDT.
Next complete advisory at 400 PM CDT.

$$
Forecaster Cangialosi