Hurricane Helene Discussion Number 10
NWS National Hurricane Center Miami FL AL092024
400 PM CDT Wed Sep 25 2024

A ragged eye is becoming apparent in visible satellite imagery and
has also been observed in recent radar data from Cancun and western
Cuba. Based on the improved structure, the initial intensity is
set at 75 kt, which is at the high end of the satellite intensity
estimates. This is also supported by the earlier Air Force Reserve
reconnaissance mission, which measured a peak 700-mb flight-level
wind of 81 kt.

Helene has turned northward (355/9 kt) and is expected to
accelerate toward the north or north-northeast during the next
24-36 hours as it moves across the Gulf of Mexico and crosses the
Florida Big Bend coast Thursday evening. After landfall, the
system is forecast to interact with a deep-layer trough to the west
and turn northwestward with a decrease in speed over the Tennessee
Valley.

The environment appears primed for significant strengthening while
Helene moves across the Gulf of Mexico. The forecast track more or
less runs along the axis of the Loop Current during the next 24
hours, where ocean temperatures are about 30 degrees Celsius. In
addition, Helene will be moving through an environment of low
vertical shear and strong upper-level divergence. Some of the
Rapid Intensification (RI) indices, particular DTOPS, respond to
this environment by indicating at least a 90 percent chance of a
35-kt increase in intensity over the next 24 hours. The NHC
intensity forecast now shows an intensity of 115 kt (Category 4) at
24 hours, which is mirrored by several of the regional hurricane
models and the SHIPS guidance. It should be noted that additional
strengthening is possible beyond 24 hours before Helene makes
landfall Thursday evening.

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 has been
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 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 is likely, and isolated major river flooding
is possible.

4. Hurricane and tropical storm conditions are expected over
northeastern portions of the Yucatan Peninsula of Mexico this
evening where Tropical Storm and Hurricane Warnings are in effect.
Tropical storm conditions are occurring over portions of western
Cuba within the Tropical Storm Warning area, and hurricane
conditions are possible this evening within the Hurricane Watch
area. 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 25/2100Z 22.5N 86.6W 75 KT 85 MPH
12H 26/0600Z 24.1N 86.2W 95 KT 110 MPH
24H 26/1800Z 27.4N 85.2W 115 KT 130 MPH
36H 27/0600Z 32.1N 84.6W 70 KT 80 MPH...INLAND
48H 27/1800Z 36.1N 86.0W 35 KT 40 MPH...POST-TROP/EXTRATROP
60H 28/0600Z 37.1N 88.1W 25 KT 30 MPH...POST-TROP/EXTRATROP
72H 28/1800Z 36.8N 88.7W 20 KT 25 MPH...POST-TROP/EXTRATROP
96H 29/1800Z 37.0N 88.0W 15 KT 15 MPH...POST-TROP/EXTRATROP
120H 30/1800Z...DISSIPATED

$$
Forecaster Berg

BULLETIN
Hurricane Helene Advisory Number 10
NWS National Hurricane Center Miami FL AL092024
400 PM CDT Wed Sep 25 2024

...HELENE STRENGTHENING...
...PREPARATIONS TO PROTECT LIFE AND PROPERTY FROM STORM SURGE AND
DAMAGING WINDS ALONG THE FLORIDA BIG BEND COAST SHOULD BE RUSHED TO
COMPLETION TODAY...


SUMMARY OF 400 PM CDT...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...22.5N 86.6W
ABOUT 460 MI...735 KM SW OF TAMPA FLORIDA
ABOUT 505 MI...815 KM SSW OF APALACHICOLA FLORIDA
MAXIMUM SUSTAINED WINDS...85 MPH...140 KM/H
PRESENT MOVEMENT...N OR 355 DEGREES AT 12 MPH...19 KM/H
MINIMUM CENTRAL PRESSURE...978 MB...28.88 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY:

The Storm Surge Watch east of Mexico Beach to Indian Pass has been
upgraded to a Storm Surge Warning.

The Tropical Storm Watch north of South Santee River to Little
River Inlet has been upgraded to a Tropical Storm Warning.

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
* Cabo Catoche to Tulum, Mexico including Cozumel

A Storm Surge Watch is in effect for...
* West of Indian Pass to Mexico Beach

A Hurricane Watch is in effect for...
* Cuban province of Pinar del Rio
* 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
* Rio Lagartos to Cabo Catoche, Mexico
* 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,
during the next 36 hours in the indicated locations. 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 warning is typically issued
36 hours before the anticipated first occurrence of
tropical-storm-force winds, conditions that make outside
preparations difficult or dangerous. 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 within the next 36 hours.

A Storm Surge Watch means there is a possibility of life-
threatening inundation, from rising water moving inland from the
coastline, in the indicated locations during the next 48 hours.
For a depiction of areas at risk, please see the National Weather
Service Storm Surge Watch/Warning Graphic, available at
hurricanes.gov.

A Hurricane Watch means that hurricane conditions are possible
within the watch area. A watch is typically issued 48 hours
before the anticipated first occurrence of tropical-storm-force
winds, conditions that make outside preparations difficult or
dangerous.

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 400 PM CDT (2100 UTC), the center of Hurricane Helene was located
near latitude 22.5 North, longitude 86.6 West. Helene is moving
toward the north near 12 mph (19 km/h). A northward or
north-northeastward motion at a faster forward speed is expected
during the next 36 hours. On the forecast track, Helene will move
across the eastern Gulf of Mexico tonight and Thursday and cross
the Florida Big Bend coast Thursday evening. After landfall,
Helene is expected to turn northwestward and slow down over the
Tennessee Valley on Friday and Saturday.

Maximum sustained winds are near 85 mph (140 km/h) with higher
gusts. Strengthening is forecast, and Helene is expected to be a
major hurricane when it reaches the Florida Big Bend coast Thursday
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.

Hurricane-force winds extend outward up to 25 miles (35 km) from the
center and tropical-storm-force winds extend outward up to 345 miles
(555 km).

The estimated minimum central pressure is 978 mb (28.88 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

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.

Storm surge could raise water levels by as much as 2 to 4 feet above
normal tide levels in areas of onshore winds along the southern
coast of Pinar del Rio, Cuba, including the Isle of Youth.

Storm surge could raise water levels by as much as 3 to 5 feet above
ground level in areas of onshore winds within the warning area along
the north coast of the Yucatan Peninsula.

WIND: Hurricane conditions are expected within the U.S. hurricane
warning area late Thursday, with tropical storm conditions
beginning Thursday morning. Tropical storm conditions are
expected in southern Florida later this evening and will spread
northward across the rest of Florida, Georgia, and South Carolina
through Thursday night.

Hurricane conditions, especially in gusts, are expected in the
hurricane warning area in Mexico during the next several hours.
Tropical storm conditions are occurring in the warning area in Cuba,
and hurricane conditions are possible for the western portion of
Cuba this evening.

RAINFALL: Hurricane Helene is expected to produce total rain
accumulations of 4 to 8 inches over western Cuba, the Cayman Islands
and the northeast Yucatan Peninsula, with isolated totals around 12
inches. 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 18 inches. This
rainfall will likely result in catastrophic and potentially
life-threatening flash and urban flooding, along with significant
river flooding. Landslides are possible 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.

TORNADOES: A tornado or two may occur tonight over parts of the
Florida Peninsula and southern Alabama. The risk of tornadoes will
increase on Thursday, expanding northward across Florida into parts
of Georgia and South Carolina.

SURF: Swells generated by Helene will affect the southern coast of
Cuba and the Yucatan Peninsula of Mexico during the next couple of
days. Swells will spread northward toward the west coast of Florida
and the northeastern Gulf Coast later today and Thursday. 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 700 PM CDT.
Next complete advisory at 1000 PM CDT.

$$
Forecaster Berg