Tropical Storm Helene Discussion Number 7
NWS National Hurricane Center Miami FL AL092024
1000 PM CDT Tue Sep 24 2024

Helene continues to become better organized with increased
convective banding features and an overall more symmetrical-looking
cloud pattern. The convection is very deep with cloud tops to -80
deg C or colder. Doppler velocity data from a NOAA Hurricane
Hunter aircraft indicate no significant vertical tilt of the
vortex in the low- to mid-troposphere. This suggests that the
vertical wind shear is low. Earlier flight-level wind data from the
aircraft indicate the the maximum winds are near 50 kt, although
this may be conservative.

Although the storm has been wobbling over the past few hours,
center fixes from the NOAA Hurricane Hunter aircraft indicate a
generally west-northwestward motion at around 300/9 kt. Helene
should turn northwestward soon as a high pressure area over Florida
shifts eastward, with the tropical cyclone center passing near the
northeastern Yucatan Peninsula tomorrow morning. Meanwhile, a
mid-tropospheric trough is digging over the Lower Mississippi
Valley. This evolution of the steering flow should cause Helene to
turn northward with an increase in forward speed during the next day
or so. An accelerating northward to north-northeastward motion over
the eastern Gulf of Mexico should take the system to the
northeastern Gulf of Mexico coast in about 48 hours. After
landfall, Helene should curve cyclonically around a mid-level low
over the south-central United States. The official forecast is very
similar to the previous one and is on top of the latest corrected
consensus track guidance.

Over the next couple of days, Helene will be moving through an
environment of low vertical wind shear, ample environmental
moisture, and over waters of high oceanic heat content. Thus,
significant strengthening is anticipated before landfall on the
northeast Gulf coast. The NHC intensity forecast explicitly shows
steady to rapid intensification (RI) of 25 kt for the next 24 hours
and 30 kt for the 24- to 48-hour forecast interval. This is in
general agreement with the SHIPS RI indices.

Helene is predicted to grow to a very large size in the NHC
forecast. 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. Tropical Storm Helene will bring heavy rain to portions of the
western Caribbean with potentially significant flooding across
western Cuba and the northeastern Yucatan Peninsula. 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 25/0300Z 19.9N 85.5W 50 KT 60 MPH
12H 25/1200Z 21.1N 86.3W 65 KT 75 MPH
24H 26/0000Z 22.7N 86.4W 75 KT 85 MPH
36H 26/1200Z 25.4N 85.5W 90 KT 105 MPH
48H 27/0000Z 29.5N 84.2W 105 KT 120 MPH
60H 27/1200Z 34.0N 84.5W 30 KT 35 MPH
72H 28/0000Z 36.5N 86.5W 20 KT 25 MPH...POST-TROP/INLAND
96H 29/0000Z 37.0N 89.0W 20 KT 25 MPH...POST-TROP/INLAND
120H 30/0000Z...DISSIPATED

$$
Forecaster Pasch

Tropical Storm Helene Advisory Number 7
NWS National Hurricane Center Miami FL AL092024
1000 PM CDT Tue Sep 24 2024

...HELENE EXPECTED TO STRENGTHEN RAPIDLY OVER THE GULF OF MEXICO...


SUMMARY OF 1000 PM CDT...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...19.9N 85.5W
ABOUT 100 MI...160 KM ESE OF COZUMEL MEXICO
ABOUT 145 MI...230 KM SSW OF THE WESTERN TIP OF CUBA
MAXIMUM SUSTAINED WINDS...60 MPH...95 KM/H
PRESENT MOVEMENT...WNW OR 300 DEGREES AT 10 MPH...17 KM/H
MINIMUM CENTRAL PRESSURE...991 MB...29.27 INCHES


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

A Tropical Storm Warning has been issued for Lake Okeechobee.

A Tropical Storm Warning has been issued from the Palm Beach/Martin
County Line northward to the Flagler/Volusia County Line.

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 including Cozumel

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
* West of Mexico Beach to the Walton/Bay County Line
* Palm Beach/Martin County Line northward to the Flagler/Volusia
County Line
* Lake Okeechobee
* Rio Lagartos to Cabo Catoche, Mexico
* Cuban provinces of Artemisa, Pinar del Rio, and the Isle of Youth

A Tropical Storm Watch is in effect for...
* Flagler/Volusia 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 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 1000 PM CDT (0300 UTC), the center of Tropical Storm Helene was
located near latitude 19.9 North, longitude 85.5 West. Helene is
moving toward the west-northwest near 10 mph (17 km/h). A turn
toward the northwest is expected later 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 later
tonight or early 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 are near 60 mph (95 km/h) with higher gusts.
Strengthening is forecast, and Helene is expected to become a
hurricane later tonight or early 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)
from the center.

The estimated minimum central pressure is 991 mb (29.27 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: Tropical Storm 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 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.
Landslides are possible in areas of steep terrain in the southern
Appalachians.

For a complete depiction of forecast rainfall associated with
Tropical Storm 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 in Florida on Wednesday and spread
northward through Thursday. Tropical storm conditions are possible
within the tropical storm watch area beginning Thursday.

TORNADOES: A tornado or two may occur Wednesday night over parts of
the western Florida peninsula and southern Alabama. The risk of
tornadoes will increase on Thursday, expanding across Florida and
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 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 100 AM CDT.
Next complete advisory at 400 AM CDT.

$$
Forecaster Pasch