459
AXNT20 KNHC 252338
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0005 UTC Thu Sep 26 2024

Tropical Weather Discussion for North America, Central America
Gulf of Mexico, Caribbean Sea, northern sections of South
America, and Atlantic Ocean to the African coast from the
Equator to 31N. The following information is based on satellite
imagery, weather observations, radar and meteorological analysis.

Based on 1800 UTC surface analysis and satellite imagery through
2330 UTC.

...SPECIAL FEATURES...

Hurricane Helene is centered near 22.5N 86.6W at 25/2100 UTC or
400 nm SW of Tampa Florida, moving N at 10 kt. Estimated minimum
central pressure is 978 mb. Maximum sustained wind speed is 75
kt with gusts to 90 kt. Seas 12 ft or greater are occurring within
180 NM in the NE quadrant, 210 NM in the SE quadrant, 90 NM in the
SW quadrant and 120 NM in the NW quadrant with peak seas near 32
ft. Strong convection is occurring within 120 NM to the south of
the center, with scattered moderate to locally strong convection
occurring within 150 NM to the north of the center. 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. A northward or
north-northeastward motion at a faster forward speed is expected
during the next 36 hours. Helene will move to 24.1N 86.2W Thu
morning, 27.4N 85.2W Thu afternoon, inland to 32.1N 84.6W Fri
morning, and continue to move inland toward the north and
northwest away from the Gulf of Mexico this weekend. 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. 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.
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.

Please read the latest HIGH SEAS FORECAST issued by the National
Hurricane Center at website -
https://www.nhc.noaa.gov/text/MIAHSFAT2.shtml and the latest
Helene NHC Forecast Advisory and Public Advisory at
www.hurricanes.gov for more details.

Invest 98L: A broad, 1009 mb low pressure system is located near
15N34W. This low is associated with a tropical wave, and
continues to produce disorganized shower and thunderstorm
activity. Seas in these waters are 5-8 ft. Environmental
conditions appear favorable for gradual development of this
system, and a tropical depression is likely to form in a few days
while it moves westward to west-northwestward across the eastern
and central tropical Atlantic. There is a medium chance of
tropical formation in the next 48 hours and a high chance of
formation in the next seven days.

Please read the latest Tropical Weather Outlook issued by the National
Hurricane Center at hurricanes.gov

...TROPICAL WAVES...

A tropical wave approaching the Lesser Antilles has been
repositioned from the previous discussion, and is located along
55W, south of 20N. Scattered moderate convection is observed from
13N to 17N and between 54W and 60W.

...MONSOON TROUGH/ITCZ...

The monsoon trough reaches the Atlantic near 17N16W and continues
westward to the 1009 mb low pres (AL98) near 15N34W and then to
13N46W. Scattered showers are noted from 06N to 16N and east of
22W.

...GULF OF MEXICO...

Please refer to the Special Features section above for details on
Hurricane Helene.

Aside from Helene, a generally dry airmass dominates the western
third of the Gulf of Mexico, except for a couple of showers west
of 95W and south of 20N. Moderate or weaker winds and slight to
moderate seas are found in these waters.

For the forecast away from the immediate impacts from Hurricane
Helene, N to NE winds will freshen tonight in the western Gulf
into Thu before slowly diminishing on Fri. Moderate to rough seas
will expand north and west across the western Gulf tonight, with
seas by Fri night. For the weekend into early next week, gentle
to moderate breezes and slight seas will prevail across the basin.

...CARIBBEAN SEA...

Please refer to the Special Features section above for details on
Hurricane Helene.

Outside of the influence of Helene, moderate to fresh SE trade winds
and moderate seas are occurring in the central Caribbean.
Moderate or weaker winds and slight to moderate seas are found in
the eastern and SW Caribbean.

For the forecast away from the immediate impacts from Hurricane
Helene, fresh to locally strong winds in the NW Caribbean will
diminish through the day on Thu. Rough to very rough seas will
slowly subside Thu night into Fri. Elsewhere, a moderate trade
regime will prevail through this weekend and into early next week
with slight seas.

...ATLANTIC OCEAN...

Please refer to the Special Features section above for details on
Hurricane Helene and Invest 98L in the central Atlantic.

A surface trough in the north-central Atlantic results in
scattered showers north of 27N and between 46W and 53W. The
remainder of the Atlantic is under the influence of a broad 1022
mb high pressure system centered south of the Azores. The pressure
gradient between this ridge and lower pressures in the deep
tropics support fresh to locally strong NE winds from 19N to 26N
and east of 27W. Seas in these waters are 4-7 ft. Moderate to
locally fresh southerly winds are present south of 10N and east of
40W, along with seas of 4-7 ft. Elsewhere, moderate or weaker
winds and moderate seas are prevalent.

For the forecast W of 55W, as Hurricane Helene moves through the
Gulf of Mexico and inland across the southeastern United States,
expect increasing winds and building seas tonight through Thu across
the waters just E of the Florida Peninsula. Winds and seas will
diminish this weekend. Elsewhere, a moderate trade regime will
prevail across much of the basin away from the potential tropical
development in the central Atlantic.

$$
ADAMS