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Atlantic Tropical Weather Discussion

AXNT20 KNHC 232312

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0005 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 1800 UTC surface analysis and satellite imagery through 
2250 UTC.


Tropical Storm Sam is centered near 11.1N 39.7W at 2100 UTC or 
1420 nm ESE of the Northern Leeward Islands moving W at 14 kt. 
Estimated minimum central pressure is 1000 mb. Maximum sustained 
wind speed is 50 kt with gusts to 60 kt. Satellite imagery 
depicts a system that is becoming better organized. Numerous 
moderate to strong convection is noted within about 50 nm of the 
center. Scattered moderate to strong convection is elsewhere in
bands within 240 nm N and 120 nm S semicircles. Peak seas are up 
to 15 ft within 90 nm of the center in the NE quadrant and within
60 nm of the center in the NW quadrant. Sam is forecast to move
WNW for the next couple of days and intensify, becoming a 
hurricane on Fri and be near major hurricane intensity by the end 
of the weekend. Please, read the read the latest HIGH SEAS 
FORECAST issued by the National Hurricane Center at website- and the latest Peter
NHC Forecast/Advisory and Public Advisory at 
for more details.

A gale-force, non-tropical low pressure system, the remnants of 
Odette, is located near 44N42W, or a little more than 550 nm 
west-northwest of the westernmost Azores. While showers and 
thunderstorms remain limited near the low, only a small increase 
in this activity could result in the formation of a subtropical or
tropical cyclone while it moves generally southeastward over 
marginally warmer waters during the next day or so. Strong upper- 
level winds are expected to develop over the system beginning 
tomorrow, 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 Also see the latest Tropical Weather Outlook at for more details.


A far eastern Atlantic tropical wave has its axis just east of 
the Cabo Verde Islands near 23W from 05N to 20N, moving westward 
at 10 kt. Scattered moderate isolated strong convection is seen 
from 05N to 12N between 16W and 27W.

A central Atlantic tropical wave has its axis along 54W from 05N
to 21N, moving westward at 10-15 kt. Scattered moderate convection
is noted from 11N to 15N between 54W and 57W. 


The monsoon trough axis passes through the the Senegalese coast 
near 15N17W to 08N22W to 08N30W. A segment of the ITCZ extends 
from 08N40W to 06N47W. Aside from convection associated to the 
tropical waves and Sam described above, scattered moderate 
isolated strong convection is from 03N to 07.5N between 26N and


An early season cold front is moving slowly across the Gulf,
extending from near Sarasota, Florida to Veracruz, Mexico. Late
morning ASCAT data passes along with current buoy observations 
indicate fresh to locally strong north to northeast winds behind 
the front. Moderate to fresh northwest winds are are along and 
just offshore the coast of Mexico from Veracruz to Tampico. Recent
altimeter satellite data along with current buoy observations are
showing seas in the range of 4-7 ft behind the front, except to 9
ft offshore of Veracruz. Generally, light to gentle breezes and 
slight seas are noted south of the front. 

Scattered moderate isolated strong convection is along and within
about 90 nm north of the front, west of 83W. A drier and stable 
air mass under high pressure is following in behind the front.

The cold front will stall tonight, then dissipate Sat. Fresh to 
strong winds will follow the front into tonight, including along 
the coast of Veracruz where seas will be around 8 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. This trough is acting on an already
very moist and unstable environment resulting in enhanced
scattered moderate to strong convection over the far south- 
central and southwestern Caribbean from along the coast of 
Colombia and Panama to 15N and between 73W-81W. A weakened 
subtropical ridge north of the area continues to support a pattern
of below average winds across the basin. Moderate trade winds are
noted over the southeast Caribbean, with generally light to 
gentle trade winds elsewhere. Seas are relatively low, in the 2-3
ft range, except for slightly higher seas of 3-4 ft across the
waters north of the A-B-C Islands.

For the forecast, Tropical Storm Sam near 10.9N 38.1W 1003 mb at 
1500 UTC, moving W at 14 kt. Maximum sustained winds are 45 kt 
with gusts to 55 kt. Sam will continue to intensify as it moves 
across the Atlantic, becoming a hurricane near 12N45W by Fri 
evening, and reaching 55W east of the Leeward Islands by Mon 
night. Meanwhile, moderate trade winds will persist over much of 
the Caribbean into early next week, becoming fresh over the south-
central Caribbean starting Fri night as high pressure builds east
of the Bahamas.


Please read the Special Features section above for details on 
newly formed Tropical Storm Sam.

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. Marine and 
aviation interests should monitor this on-going situation by 
reading Volcanic Ash Advisory issued by Meteo- France at /la- palma/. The next advisory will
be issue no later than 23/2300 UTC.

A stationary front extends from near 31N45W to 27N68W. Morning 
ASCAT data depicted moderate to mainly fresh east to southeast 
winds north of the stationary front between 56W-59W. A cold front 
has moved off the southeastern United States coast and extends 
from 31N78W to inland central Florida. A pre-frontal trough 
extends just SE of the front to inland South Florida. Satellite 
imagery shows scattered showers and thunderstorms north of 26N 
and between 73W-79W. Broken to overcast multilayered clouds with 
embedded areas of rain along with scattered and isolated 
thunderstorms are seen north of 25N between 57W-64W. The 1009 mb 
remnant low of Peter is near 24N67W. A trough extends northeast 
from the low to 26N64W, and southwest from the low to the north- 
central coast of Hispaniola. An expanding area of scattered 
moderate to isolated strong convection is well removed to the east
of the low from 22N to the stationary front and between 60W- 65W.
Similar activity is also from 19N to 22N between 63W-67W. Morning
ASCAT data showed fresh to strong southerly winds with this 
convective activity. Altimeter data indicates seas up to 7 ft 
northeast and east of the low from 22N to 28N between 62W-67W. 
Seas may be slighter higher in the strong convection.

The post-tropical cyclone remnant 1010 mb low of former tropical 
cyclone Rose is near 27N42W. A trough to its southwest extends 
from 23N45W to 19N48W. Morning altimeter pass has seas up to 11 
ft within about 60 nm in the northwest quadrant of this low. This 
attributed to a large area of northerly swell that is producing 
seas of 8-12 ft seas north of 22N between 35W-60W. Fresh east to 
southeast winds are over the eastern semicircle of the low. The 
low will gradually dissipate through Sat. Aside from the features 
and related winds and seas already mentioned in this discussion, 
moderate to occasionally fresh trade winds are noted across the 
basin along with 4 to 6 ft seas in open waters. 

For the forecast west of 65W, a cold front extending from 31N78W 
to Cape Canaveral, Florida will stall from 31N77W to near Fort 
Pierce, Florida by tonight, then dissipate through early Sun just 
before a second weak front possibly moves into the region late 
Sun. Farther east, Tropical Storm Sam will intensify to a 
hurricane by Fri afternoon near 12N44W and to a major hurricane 
Sat afternoon near 13N47W. Sam will reach near 15N 52.5W Mon and 
be near 17.5N 55.5W Tue.