9 months 3 weeks ago
Issued at 400 AM CDT Wed Sep 25 2024
000
WTNT44 KNHC 250854
TCDAT4
Tropical Storm Helene Discussion Number 8
NWS National Hurricane Center Miami FL AL092024
400 AM CDT Wed Sep 25 2024
Helen has strengthened some since the last advisory. Reports from
an Air Force Reserve Hurricane Hunter aircraft indicate that
the central pressure has fallen to 985 mb, and that the maximum
850 mb flight-level were 58 kt in the northeastern quadrant. A
dropsonde in the northwest quadrant reported a splash wind of 59
kt, but the boundary-layer average suggested sustained winds closer
to 45 kt. Based on these data and increasing satellite intensity
estimates, the initial intensity is increased to 55 kt. Despite
the increased intensity, the aircraft data, along with radar data
from Mexico and Cuba, show that Helen has not yet formed a
well-defined inner core.
The initial motion is 325/8 kt. Helen should turn northward during
the next 12 h or so on the western side of a mid-level ridge, and
then it should accelerate northward to north-northeastward as it
become embedded in the deep-layer flow between the ridge and a
mid-latitude trough/developing cut-off low over the Mississippi
valley. This motion should bring the center near the northeastern
coast of the Yucatan Peninsula this morning, then across the
eastern Gulf of Mexico tonight and Thursday to a landfall along the
northeast coast of the Gulf of Mexico late Thursday or Thursday
night. After landfall, Helene should curve cyclonically around the
cut-off low until it dissipates. The new forecast track is little
changed from the previous track.
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. All
guidance forecasts steady to rapid intensification, including the
RI indices associated with the SHIPS model. The latest forecast
calls for a 105 kt intensity by 36 h, and this could be
conservative as some of the guidance is stronger. After landfall,
Helen is forecast to weaken and become post-tropical as it gets
tangled up in the baroclinic system over the southeastern United
States.
Helene's wind field 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 Helene 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 during the next several hours, 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
completed 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
and potentially life-threatening flash and urban flooding is
expected across portions of Florida, the Southeast, the Southern
Appalachians, and the Tennessee Valley beginning today 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 25/0900Z 20.7N 86.2W 55 KT 65 MPH
12H 25/1800Z 21.9N 86.5W 70 KT 80 MPH
24H 26/0600Z 24.1N 86.2W 90 KT 105 MPH
36H 26/1800Z 27.4N 85.0W 105 KT 120 MPH
48H 27/0600Z 32.0N 84.2W 65 KT 75 MPH...INLAND
60H 27/1800Z 35.9N 85.4W 30 KT 35 MPH...POST-TROP/INLAND
72H 28/0600Z 37.0N 87.8W 20 KT 25 MPH...POST-TROP/INLAND
96H 29/0600Z 36.5N 88.0W 20 KT 25 MPH...POST-TROP/INLAND
120H 30/0600Z...DISSIPATED
$$
Forecaster Beven
NHC Webmaster
9 months 3 weeks ago
Issued at 400 AM CDT Wed Sep 25 2024
000
WTNT34 KNHC 250853
TCPAT4
BULLETIN
Tropical Storm Helene Advisory Number 8
NWS National Hurricane Center Miami FL AL092024
400 AM CDT Wed Sep 25 2024
...HELENE STRENGTHENING AS THE CENTER APPROACHES THE NORTHEASTERN
COAST OF THE YUCATAN PENINSULA...
...NEW TROPICAL STORM WATCHES AND WARNINGS FOR PORTIONS OF THE
UNITED STATES...
SUMMARY OF 400 AM CDT...0900 UTC...INFORMATION
----------------------------------------------
LOCATION...20.7N 86.2W
ABOUT 45 MI...75 KM ENE OF COZUMEL MEXICO
ABOUT 120 MI...190 KM SW OF THE WESTERN TIP OF CUBA
MAXIMUM SUSTAINED WINDS...65 MPH...100 KM/H
PRESENT MOVEMENT...NW OR 325 DEGREES AT 9 MPH...15 KM/H
MINIMUM CENTRAL PRESSURE...985 MB...29.09 INCHES
WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY:
A Tropical Storm Warning is now in effect for the Upper Florida
Keys from the Channel 5 Bridge to Ocean Reef and for the southern
Florida Peninsula east of Flamingo to the Palm Beach/Martin County
line.
A Tropical Storm Warning is now in effect for the northeast coast
of Florida north of the Flagler/Volusia line to the mouth of the
St. Mary's River.
A Tropical Storm Watch is now in effect for the South Carolina
coast north of the Savannah River to the South Santee River.
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
* All of the Florida Keys
* The Florida west coast from Flamingo to Anclote River, including
Tampa Bay
* West of Mexico Beach to the Walton/Bay County Line
* The Florida east coast from Flamingo northward to the mouth of
the St. Mary's River
* 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...
* The Georgia and South Carolina coast north of the mouth
of the St. Mary's River to the South Santee 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 later today.
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 AM CDT (0900 UTC), the center of Tropical Storm Helene was
located near latitude 20.7 North, longitude 86.2 West. Helene is
moving toward the northwest near 9 mph (15 km/h). This motion
should continue through this morning, followed by a general
northward motion beginning later today and continuing through
Friday. On the forecast track, the center of Helene will pass near
the northeastern coast of the Yucatan Peninsula this morning, move
across the eastern Gulf of Mexico on later today and Thursday, and
reach the Big Bend coast of Florida late Thursday.
Maximum sustained winds are now near 65 mph (100 km/h) with higher
gusts. Strengthening is forecast, and Helene is expected to become
a hurricane later today. 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. A Mexican Navy weather station at Isla Contoy
recently reported sustained winds of 38 mph (61 km/h) and a wind
gust of 48 mph (78 km/h).
The minimum central pressure recently reported by an Air Force
Reserve Hurricane Hunter aircraft is 985 mb (29.09 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
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 5 to 10 inches with isolated totals around 15
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 during the next several hours, with tropical storm
conditions already ongoing. Hurricane conditions are expected within
the U.S. hurricane warning area late Thursday. Hurricane conditions
are possible for the western portion of Cuba later today. Tropical
storm conditions are expected to begin in the warning area in Cuba
during the next several hours. Tropical storm conditions are
expected in southern Florida later today and spreading northward
through Thursday. Tropical storm conditions are possible within the
tropical storm watch area beginning Thursday and Thursday night.
TORNADOES: A tornado or two may occur tonight 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 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 AM CDT.
Next complete advisory at 1000 AM CDT.
$$
Forecaster Beven
NHC Webmaster
