AXNT20 KNHC 241204
Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1205 UTC Fri Sep 24 2021
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 0600 UTC surface analysis and satellite imagery through
Hurricane Sam is centered near 11.5N 42.2W at 24/0900 UTC or
1280 nm ESE of the Northern Leeward Islands moving W at 13 kt.
Estimated minimum central pressure is 993 mb. Maximum sustained
wind speed is 65 kt with gusts to 80 kt. Satellite
imagery depicts numerous moderate to strong convection is from 09N
to 16N between 39W and 45W. Peak seas are currently near 20 ft.
A decrease in forward speed and a motion toward the west-
northwest are expected over the weekend. Rapid intensification is
forecast to continue, and Sam is likely to become a major
hurricane tonight or early Saturday. Please read the latest NHC
Public Advisory at https://www.nhc.noaa.gov/text/MIATCPAT3.shtml
and Forecast/ Advisory at
https://www.nhc.noaa.gov/text/MIATCMAT3.shtml for more details.
A gale-force, non-tropical low pressure system is centered near
44N41W, or a little more than 525 nm west-northwest of the
westernmost Azores. Showers and thunderstorms remain limited
near the low, and this system has only a brief window of opportunity
to become a subtropical or tropical cyclone while it moves generally
south-southeastward over marginally warmer waters. Strong upper-
level winds are expected to develop over the system by late today,
which should then limit further development. Additional
information on this system, including gale warnings, can be found
in High Seas Forecasts issued by the Ocean Prediction Center
ocean.weather.gov. Also see the latest Tropical Weather Outlook at
www.hurricanes.gov for more details.
A large area of showers and thunderstorms centered a couple
hundred miles east of Bermuda is associated with a formative
surface low interacting with an upper-level trough. Additional
tropical or subtropical development of this system could occur
through early Saturday as it moves generally north-
northwestward. After that time, development is not expected due
to strong upper-level winds. This system has a medium chance of
tropical cyclone development during the next 48 hours.
Additional information on this system, including gale warnings,
can be found in High Seas Forecasts issued by the Ocean
Prediction Center ocean.weather.gov. Also see the latest
Tropical Weather Outlook at www.hurricanes.gov for more details.
An Atlantic tropical wave has its axis along 25W, south of 20N,
and it is moving W at 10 kt. Scattered showers are noted within 45
nm on either side of the wave axis mainly south of 13N. The
northern part of the wave is embedded in dry Saharan air,
inhibiting the development of showers and thunderstorms.
An Atlantic tropical wave has its axis along 56W, south of 20N,
and it is moving W at 10-15 kt. Scattered showers are noted within 45
nm on either side of the wave axis mainly south of 14N.
The monsoon trough passes through coast of Senegal near 14N17W to
06N28W. A segment of the ITCZ extends from 06N28W to 09N37W and
another segment continues from 07N47W to 06N55W. Aside from
convection associated to the tropical waves and Sam described
above, scattered showers prevail along the ITCZ between 28W and
GULF OF MEXICO...
The main feature of interest in the Gulf of Mexico is frontal
boundary that traverses the basin from SW Florida to Veracruz. The
front is analyzed as stationary in the southern Gulf waters. A
few showers and thunderstorms are noted along the boundary. The
airmass behind the front is quite dry, allowing fairly tranquil
weather conditions front Texas to Florida in the N Gulf. Recent
scatterometer satellite data depicts fresh NE winds behind the
frontal boundary in the central Gulf, especially from 25N to 28N
and between 85W and 90W. Fresh to locally strong N-NE winds are
depicted in the SW Gulf, especially near the coast of Veracruz.
Seas behind the front are 4-6 ft and 2-4 ft ahead of the boundary.
For the forecast, the front will dissipate by Sat. Fresh winds
prevail within 100 nm north of the front with seas ranging between
4 to 6 ft. Looking ahead, winds and seas will diminish across
basin from Sat and into early next week as high pressure builds
over the northern Gulf.
A sharp upper-level trough extends from the vicinity of the
southeastern Bahamas to across eastern Cuba and to the
southwestern Caribbean. A surface trough is analyzed in the W
Caribbean extending along 84W from 17N-22N. This is allowing for
the development of afternoon and evening thunderstorms across the
western and central Caribbean Sea. Scattered moderate convection
is also noted in the SW and south- central Caribbean, especially
near the northern coast of Colombia. A recent scatterometer pass
indicate fresh trades within 130 nm of the coast of NW Venezuela,
including the waters surrounding the ABC islands, while gentle to
moderate trades prevail elsewhere. Seas in the central and E
Caribbean are 2-4 ft, while 1-2 ft are noted elsewhere.
For the forecast, Hurricane Sam is near 11.5N 42.2W 993 mb at 5
AM EDT moving W at 13 kt. Maximum sustained winds 65 kt gusts 80
kt. Sam will move to 11.7N 44.0W this afternoon, 12.1N 45.9W Sat
morning, 12.5N 47.4W Sat afternoon, 12.9N 48.7W Sun morning, 13.4N
50.0W Sun afternoon, and 14.1N 51.1W Mon morning. Sam will change
little in intensity as it moves to 15.9N 53.8W by early Tue.
Meanwhile, moderate trade winds will persist over much of the
Caribbean into early next week, becoming fresh over the south-
central Caribbean starting tonight as high pressure builds east of
the Bahamas. Fresh to strong winds are forecast in the Gulf of
Honduras Sun night.
Please read the sections above for details on Hurricane Sam and
tropical waves moving across the basin.
The Cumbre Vieja volcano on the island of La Palma in the Canary
Islands has been erupting since 19/1410 UTC. A significant ash
emission is ongoing in the vicinity of the volcano below 10,000 ft.
Marine and aviation interests should monitor this on-going
situation by reading Volcanic Ash Advisory issued by Meteo-France
at http://vaac.meteo.fr/volcanoes/la-palma/. The next advisory
will be issue no later than 24/1500 UTC.
A cold front extends from 31N76W to 27N80W. A pre-frontal trough
is noted just ahead of the cold front from 28N78W to South
Florida. Scattered moderate convection is observed on satellite
imagery N of 27N and W of 74W. Recent satellite-derived wind data
show fresh to locally strong SE-S winds from 27N to 31N and
between 73W and 76W. Seas in this region are ranging between 4-6 ft.
Another area of interest is a sharp surface trough extending from
31N60W to 25N65W and the 1009 mb low near 23N67W. The interaction
of these features with an upper-level low near Bermuda is
inducing a large area of showers and thunderstorms, especially
from N of 20N and between 56W and 64W. Scatterometer wind data
indicate fresh to strong cyclonic winds near the northern end of
the surface trough, N of 28N. Seas in this region are 5-8 ft, with
the highest seas noted near the highest winds.
Farther east, the 1010 mb low is located near 28N43W. Scattered
showers and thunderstorms are noted N of 26N between 35W-40W.
A stationary front is analyzed from 31N46W to 27N54W with no
significant convection. Fresh northerly winds are found off the
coast of Mauritania, mainly E of 20W. A large area of northerly
swell that is producing 8-11 ft seas N of 22N and between 35W and
60W. Moderate to fresh trade winds are noted elsewhere across the
basin along with 4 to 6 ft seas in open waters.
For the forecast west of 65W, the cold front will stall then
dissipate through early Sun just before a second weak front
possibly moves into the region late Sun. Farther east, Hurricane
Sam is centered near 11.5N 42.2W 993 mb at 5 AM EDT, moving W at
13 kt. Maximum sustained winds 65 kt gusts 80 kt. Sam will move to
11.7N 44.0W this afternoon, 12.1N 45.9W Sat morning, 12.5N 47.4W
Sat afternoon, 12.9N 48.7W Sun morning, 13.4N 50.0W Sun afternoon,
and 14.1N 51.1W Mon morning. Sam will change little in intensity
as it moves to 15.9N 53.8W by early Tue.