Tropical Storm Helene Discussion Number 6
NWS National Hurricane Center Miami FL AL092024
500 PM EDT Tue Sep 24 2024

Deep convection is gradually filling in within Helene's
circulation, and the well-defined center that formed earlier this
morning is now obscured by cloudiness and showers. Data from NOAA
buoy indicate that the central pressure has fallen to 995 mb, and
the initial intensity is therefore estimated to be 45 kt. NOAA and
the Air Force Reserve Hurricane Hunters will be investigating Helene
this evening to provide more information about the storm's intensity
and structure.

With the center formation this morning, Helene has taken a
short-term jog to the west-northwest (300/10 kt). The storm is
expected to turn northwestward by tonight and then northward on
Wednesday as high pressure over Florida shifts eastward, and a
deep-layer trough digs southward over the Lower Mississippi Valley.
The NHC track forecast has been shifted westward during the first
24 hours to account for the recent motion, and Helene's center
could get very close to the northeastern coast of the Yucatan
Peninsula Wednesday morning. After that time, however, the NHC
track forecast is relatively unchanged from the previous
prediction, except for being a little bit slower based on the
latest guidance. Helene is expected to accelerate while it moves
northward across the eastern Gulf of Mexico and approaches the
Florida Gulf coast.

Warm sea surface temperatures, decreasing shear, and strong
upper-level divergence are likely to foster Helene's strengthening
while it moves across the northwestern Caribbean Sea and eastern
Gulf of Mexico. The statistical-dynamical SHIPS/LGEM models, as
well as the regional hurricane models, continue to show Helene
reaching major hurricane intensity while over the eastern Gulf of
Mexico, and that continues to be shown in the NHC forecast. Helene
could maintain that level of intensity until it reaches the Gulf
coast of Florida.

Of equal importance to the forecast intensity is Helene's forecast
size. Helene's forecast radii are at the 90th percentile of
major hurricane size at similar latitudes, and 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 it 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 on Wednesday, 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
complete by early Thursday since tropical storm conditions are
expected to begin within this area on Thursday.

4. Helene will bring heavy rain to portions of the western Caribbean
with potentially significant flooding and mudslides across western
Cuba. Considerable flash and urban flooding is expected across
portions of Florida, the Southeast, southern Appalachians, and the
Tennessee Valley Wednesday 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 24/2100Z 19.7N 84.7W 45 KT 50 MPH
12H 25/0600Z 20.4N 86.0W 55 KT 65 MPH
24H 25/1800Z 21.7N 86.6W 65 KT 75 MPH
36H 26/0600Z 23.7N 86.1W 80 KT 90 MPH
48H 26/1800Z 27.0N 84.9W 100 KT 115 MPH
60H 27/0600Z 31.5N 84.0W 60 KT 70 MPH...INLAND
72H 27/1800Z 35.5N 84.8W 30 KT 35 MPH...INLAND
96H 28/1800Z 38.2N 89.0W 20 KT 25 MPH...POST-TROP/INLAND
120H 29/1800Z...DISSIPATED

$$
Forecaster Berg

Tropical Storm Helene Advisory Number 6
NWS National Hurricane Center Miami FL AL092024
500 PM EDT Tue Sep 24 2024

...STORM SURGE AND HURRICANE WARNINGS ISSUED FOR THE GULF COAST OF
FLORIDA...
...HELENE'S LARGE SIZE WILL LIKELY CAUSE AN EXTENSIVE AREA TO BE
AFFECTED BY THE STORM'S HAZARDS...


SUMMARY OF 500 PM EDT...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...19.7N 84.7W
ABOUT 155 MI...245 KM ESE OF COZUMEL MEXICO
ABOUT 150 MI...245 KM S OF THE WESTERN TIP OF CUBA
MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H
PRESENT MOVEMENT...WNW OR 300 DEGREES AT 12 MPH...19 KM/H
MINIMUM CENTRAL PRESSURE...995 MB...29.39 INCHES


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

A Storm Surge Warning has been issued from Flamingo to Indian Pass,
Florida, including Tampa Bay and Charlotte Harbor.

A Hurricane Warning has been issued from Anclote River to Mexico
Beach, Florida.

The government of Mexico has issued a Hurricane Warning from Cabo
Catoche to Tulum.

A Tropical Storm Warning has been issued for the Middle Florida Keys
from the Seven Mile Bridge to the Channel 5 Bridge. A Tropical
Storm Warning has been issued for the Gulf coast of Florida from
Flamingo northward to Anclote River, including Tampa Bay, and west
of Mexico Beach to the Walton/Bay County Line.

A Tropical Storm Watch has been issued for the east coasts of
Florida and Georgia from the Palm Beach/Martin County Line northward
to the Savannah River, and for Lake Okeechobee.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT:

A Storm Surge Warning is in effect for...
* Indian Pass southward to Flamingo
* Tampa Bay
* Charlotte Harbor

A Hurricane Warning is in effect for...
* Anclote River to Mexico Beach, Florida
* Cabo Catoche to Tulum, Mexico

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...
* Dry Tortugas
* Lower and Middle Florida Keys west of the Channel 5 Bridge
* Flamingo to Anclote River, including Tampa Bay
* Rio Lagartos to Tulum, Mexico
* Cuban provinces of Artemisa, Pinar del Rio, and the Isle of Youth

A Tropical Storm Watch is in effect for...
* Lake Okeechobee
* Palm Beach/Martin County Line northward to the Savannah River

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 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.

A Tropical Storm Watch means that tropical storm conditions are
possible within the watch area.

Additional watches or warnings may be required for portions of
Florida and the southeastern United States tonight or on Wednesday.

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 center of Tropical Storm Helene was
located near latitude 19.7 North, longitude 84.7 West. Helene is
moving toward the west-northwest near 12 mph (19 km/h). A turn
toward the northwest is expected tonight, followed by a general
northward motion beginning on Wednesday and continuing through
Friday. On the forecast track, the center of Helene will pass near
the northeastern coast of the Yucatan Peninsula on Wednesday, move
across the eastern Gulf of Mexico on Wednesday and Thursday, and
reach the Big Bend coast of Florida late Thursday.

Maximum sustained winds have increased to near 50 mph (85 km/h)
with higher gusts. Additional strengthening is forecast, and
Helene is expected to become a hurricane on Wednesday. The storm
is forecast to rapidly strengthen over the eastern Gulf of Mexico
and become a major hurricane on Thursday.

Tropical-storm-force winds extend outward up to 175 miles (280 km)
to the east of the center.

Data from NOAA buoy 42056 indicate that the minimum central pressure
is 995 mb (29.39 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

RAINFALL: Helene is expected to produce total rain accumulations of
4 to 8 inches over western Cuba and the Cayman Islands with isolated
totals around 12 inches. Over the eastern Yucatan Peninsula, 4 to 6
inches of rain are expected with isolated totals over 8 inches.
This rainfall brings a risk of considerable flooding.

Over the Southeastern U.S., Helene is expected to produce total rain
accumulations of 4 to 8 inches with isolated totals around 12
inches. This rainfall will likely result in areas of considerable
flash and urban flooding, with areas of significant river flooding
likely, including the risk of landslides in areas of steep terrain
in the southern Appalachians.

For a complete depiction of forecast rainfall associated with
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.

STORM SURGE: The combination of a dangerous 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...

Ochlockonee River, FL to Chassahowitzka, FL...10-15 ft
Chassahowitzka, FL to Anclote River, FL...6-10 ft
Indian Pass, FL to Ochlockonee River, FL...5-10 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
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 2 to 4 feet above
ground level in areas of onshore winds within the warning area along
the east coast of the Yucatan Peninsula.

WIND: Hurricane conditions are expected in the hurricane warning
area in Mexico on Wednesday. Hurricane conditions are
expected within the U.S. hurricane warning area late Thursday.
Tropical storm conditions are expected to begin in the
tropical storm warning area Florida on Wednesday and spread
northward through Thursday. Tropical storm conditions are possible
within the tropical storm watch area beginning Thursday.

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 on Wednesday 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 800 PM EDT.
Next complete advisory at 1100 PM EDT.

$$
Forecaster Berg