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Atlantic Tropical Weather Discussion



000
AXNT20 KNHC 241204
TWDAT 

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 
1145 UTC.

...SPECIAL FEATURES... 

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.

...TROPICAL WAVES...

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.

...MONSOON TROUGH/ITCZ...

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
37W. 

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. 

CARIBBEAN SEA...

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.

ATLANTIC OCEAN...

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.  

$$
ERA