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Atlantic Tropical Weather Discussion



000
AXNT20 KNHC 251034
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1205 UTC Sat Sep 25 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 
1030 UTC.

...SPECIAL FEATURES... 

Hurricane Sam is centered near 12.8N 46.7W at 25/0900 UTC or
1000 nm ESE of the Northern Leeward Islands moving WNW at 11 kt.
Estimated minimum central pressure is 973 mb. Maximum sustained
wind speed is 95 kt with gusts to 115 kt. Numerous moderate to
strong convection is noted from 10N-15N between 43W-48W. Peak 
seas near the center are estimated near 23 ft and expected to 
reach 31 ft by Sunday morning. A slower motion to the west- 
northwest is expected over the weekend, followed by a turn to the 
northwest on Monday. Additional strengthening is forecast, and Sam
is expected to become a major hurricane later today. 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.

Subtropical Storm Teresa is centered near 34.5N 65.5W at 25/0900
UTC or 130 nm NNW of Bermuda moving WNW at 5 kt. Estimated
minimum central pressure is 1009 mb. Maximum sustained wind
speed is 35 kt with gusts to 45 kt. Scattered moderate
isolated strong convection is seen well removed from the center, 
and occurring within 200 nm across the N and 400 nm across the NE
quadrants. A turn to the north is expected later today, followed 
by a northeastward motion after that. Teresa is expected to become
a remnant by tonight and dissipate on Sunday. Please see the 
latest High Seas Forecasts issued by the Ocean Prediction Center 
at https://ocean.weather.gov/shtml/NFDHSFAT1.php and the latest 
NHC Forecast/Advisory and Public Advisory on Teresa at 
www.hurricanes.gov for more details.

...TROPICAL WAVES...

An Atlantic tropical wave has its axis along 30W, south of 19N, 
and it is moving W at 10-15 kt. A few showers are noted near the 
southern portion of the wave. Satellite imagery show that the 
northern part of the wave remains embedded in dry Saharan air, 
inhibiting the development of shower and thunderstorm activity. 

A tropical wave extends across the Lesser Antilles and into E
Venezuela. It has its axis near 66W, south of 20N, and it is 
moving W near 15 kt. A few showers are noted near the wave axis.

...MONSOON TROUGH/ITCZ...

The monsoon trough passes through coast of Senegal near 12N17W to
06N30W and to 07N38W. A segment of the ITCZ extends from 07N38W 
to 09N42W and another segment continues from 09N51W to 07N58W. 
Aside from convection associated to the tropical waves and Sam 
described above, scattered showers are noted within 200 nm on
either side of the monsoon trough.

GULF OF MEXICO...

A stationary front meanders across the southern Gulf of Mexico
from SW Florida to Veracruz. A few showers are noted on infrared
satellite imagery along the frontal boundary. The air mass behind
the front is quite dry, allowing fairly tranquil weather 
conditions across the northern and western Gulf, from Florida to
northern Veracruz. Satellite-derived wind data and surface
observations indicate that moderate to fresh winds dominate the 
basin, with the strongest winds occurring in the central Gulf. 
Seas in the central and SW Gulf are 3-5 ft, and 1-3 ft elsewhere.

For the forecast, a stationary front extends across the southern Gulf
from Naples, Florida to Veracruz, Mexico. This boundary will
dissipate by tonight. Moderate to fresh winds prevail north of 
the front. Winds and sea through early next week as high pressure
builds over the northern Gulf. 

CARIBBEAN SEA...

Refer to the section above for details on the tropical wave moving
across the easter Caribbean.

Scattered moderate convection is noted within 100 nm of the coast
of NE Honduras, Nicaragua and northern Costa Rica. A surface 
trough extends from the Yucatan Channel to northern Honduras, with
no significant convection at this time. The surface trough is 
quite evident in a recent scatterometer satellite pass, showing 
broad troughiness over the Gulf of Honduras. The remainder of the
Caribbean enjoys fairly tranquil weather conditions thanks to a 
drier environment. Satellite-derived wind data indicate fresh to 
strong trades in the south-central Caribbean, mainly within 170 
nm of the northern coast of Colombia. Gentle to moderate trades 
are found in the rest of the basin. Seas of 3-5 ft are present in 
the central and eastern Caribbean, with the highest seas occurring
in the south-central portion of the basin. Elsewhere, seas range
between 1-3 ft.

For the forecast, Hurricane Sam will move to 13.1N 48.0W this 
afternoon, 13.5N 49.3W Sun morning, 14.0N 50.4W Sun afternoon, 
14.7N 51.5W Mon morning, 15.4N 52.5W Mon afternoon, and 16.3N 
53.7W Tue morning. Sam will change little in intensity as it moves
to 18.0N 56.0W by early Wed. Meanwhile, moderate trade winds will
persist over much of the Caribbean into early next week, while 
fresh winds prevail over the south-central Caribbean as high 
pressure builds east of the Bahamas. 

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. The height of the 
ash plume cloud is difficult to estimate due to cloud cover. 
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 25/1500 UTC.

A cold front just east of the United States continues its eastward
progression across the NW Atlantic. The southern portion of this
front transitions to a stationary front from 31N75W to the
Treasure Coast of Florida near 27N80W. A pre-frontal surface 
trough is analyzed from 31N74W to SW Florida. Scattered showers
are observed on infrared satellite imagery from 23N to 28N and W 
of 73W. A recent scatterometer satellite pass depicted fresh to 
strong southerly winds in the central Bahamas in association with 
the convection affecting the area. Another surface trough extends 
from 31N62W to the 1011 mb remnant low of Peter near 25N65W to 
21N68W. The interaction of these features with an upper-level 
trough to the north results in an area of showers and 
thunderstorms from 23N to 27N and between 60W and 65W. Satellite-
derived wind data show fresh to locally strong winds to the east 
of the surface trough, likely associated with the convection in 
the area. Seas W of 60W are 3-6 ft.

Farther east, a surface trough extends from 31N37W to 27N38W. In 
the vicinity of this feature is a stationary front that stretches 
from 31N38W to 28N50W. An upper level trough nearby is 
interacting with these features, inducing a large area of 
scattered moderate convection N of 26N and between 31W and 35W. 
Satellite-derived wind data depict fresh to strong southerly 
winds N of 25N and between 36W and 40W, likely associated with the
convection. Moderate to fresh northerly winds are found off the 
coast of Mauritania, mainly east of 20W. E of 60W and N of 20N, 
seas are 5-8 ft, with the highest seas found off the coast of 
Mauritania. In the rest of the basin, moderate to fresh trade 
winds are noted along with 4 to 6 ft seas. 

For the forecast, the front extending from 31N75W to West Palm
Beach, Florida, will remain stationary and weaken through early 
Sun. Then, reinforcing moderate N winds will push the front 
eastward as a weak cold front, reaching from 31N69W to 27N74W by 
Mon morning. The front will stall and dissipate Tue. Farther east,
Hurricane Sam near 12.8N 46.7W 973 mb at 5 AM EDT 
moving WNW at 11 kt. Maximum sustained winds 95 kt gusts 115 kt.
Sam will move to 13.1N 48.0W this afternoon, 13.5N 49.3W Sun 
morning, 14.0N 50.4W Sun afternoon, 14.7N 51.5W Mon morning, 
15.4N 52.5W Mon afternoon, and 16.3N 53.7W Tue morning. Sam will 
change little in intensity as it moves to 18.0N 56.0W by early 
Wed.

$$
ERA