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Atlantic Tropical Weather Discussion



000
AXNT20 KNHC 261014
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1205 UTC Sun Sep 26 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 
1000 UTC.

...SPECIAL FEATURES... 

Hurricane Sam is centered near 13.8N 49.7W at 26/0900 UTC or 820
nm ESE of the Northern Leeward Islands moving WNW at 7 kt.
Estimated minimum central pressure is 943 mb. Maximum sustained
wind speed is 125 kt with gusts to 150 kt. Satellite imagery shows 
numerous moderate to strong convection within 90 nm of Sam's 
center. Sam is a category 4 hurricane on the Saffir-Simpson 
Hurricane Wind Scale. Some fluctuations in intensity are expected 
during the next day or so. Hurricane-force winds extend outward 
up to 30 nmi from the center and tropical-storm-force winds extend
outward up to 90 nmi. Thereafter, some slow weakening is 
forecast. Please read the latest High Seas Forecast issued by NHC
at http://www.nhc.noaa.gov/text/MIAHSFAT2.shtml and the latest 
NHC Public Advisory and Forecast/Advisory at https://hurricanes.gov
for more details.

...TROPICAL WAVES...

An Atlantic tropical wave has its axis along 24W, south of 17N, 
moving W around 10 kt. Scattered showers are noted from 11N-14N 
between 20W-27W.

Another Atlantic tropical wave has its axis along 35W, south of 
16N, moving W around 10 kt. Scattered moderate convection is 
observed from 05N and 10N between 30W and 40W. Satellite imagery 
show that the northern part of the wave remains embedded in dry 
Saharan air, inhibiting the development of shower and thunderstorm
activity to the north of 11N. 

A Caribbean tropical wave has its axis along 69W, south of 20N, 
and it is moving W around 10-15 kt. No significant deep convection
is noted over water in association with this wave. 

...MONSOON TROUGH/ITCZ...

The monsoon trough passes through coast of Guinea-Bissau near 
12N16W to 07N39W. The ITCZ extends from 07N39W to 09N44W. Aside 
from convection associated to the tropical waves and Sam described
above, scattered moderate convection is seen within 200 nm of the
monsoon trough and ITCZ between 20W-46W.

GULF OF MEXICO...

A surface trough extends from 27N85W to 22N94W with scattered
showers. Dry air dominates the rest of the basin, allowing for 
fairly tranquil weather conditions. A weak pressure gradient 
across the Gulf results in moderate to locally fresh E-NE winds, 
with the strongest winds occurring in the central Gulf, north of 
the surface trough. Seas W of 88W are 3-5 ft, with the highest 
seas occurring in the central Gulf. Seas E of 88W are 1-3 ft.

For the forecast, winds and seas will diminish across the basin 
through Mon as high pressure builds over the northern Gulf.

CARIBBEAN SEA...

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

The eastern extension of the E Pacific monsoon trough and abundant
moisture results in scattered moderate to isolated strong
convection within 130 nm of the coast of Nicaragua, Costa Rica,
Panama and NW Colombia. The rest of the Caribbean is dominated by
a fairly dry weather pattern. 

A modest north-south pressure gradient persists in the south-central
Caribbean between a broad Colombian Low and weak ridging north of
the basin. Recent scatterometer satellite data indicate that 
fresh to strong trades are occurring within 200 nm of the north 
coast of Colombia and 70 nm of the coast of NW Venezuela, 
encompassing the Gulf of Venezuela and the waters surrounding the
ABC islands. Gentle to moderate trades prevail elsewhere. Seas 
are 4-6 ft over the south-central Caribbean and 2-4 ft elsewhere.

Looking ahead, Hurricane Sam is near 13.8N 49.7W 943 mb at 5 AM 
EDT moving WNW at 7 kt. Maximum sustained winds 125 kt gusts 150 
kt. Sam will move to 14.3N 50.6W this afternoon, 15.0N 51.8W Mon 
morning, 15.8N 52.9W Mon afternoon, 16.6N 53.9W Tue morning, 17.5N
55.0W Tue afternoon, and 18.4N 56.3W Wed morning. Sam will change
little in intensity as it moves to 20.8N 59.3W by early Thu. 
Meanwhile, moderate trade winds will persist over much of the 
Caribbean into early next week. Fresh winds will prevail over the 
south-central Caribbean as high pressure builds east of the 
Bahamas through midweek.

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. Significant 
volcanic ash mainly 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 
http://vaac.meteo.fr/volcanoes/la-palma/. The next advisory will 
be issued no later than 26/1500 UTC.

A surface trough is currently analyzed from 31N74W to 25N78W.
Scattered showers are noted in the vicinity of the trough
affecting the northern Bahamas. A 1014 mb low pressure is located
near 27N63W, with a surface trough extends across the low 
pressure from 31N62W to 23N66W. A large area of showers and 
thunderstorms is found east of the trough axis from 24N to 30N
between 58W and 64W. A recent scatterometer satellite pass show 
fresh southerly winds associated with the convection. To the east,
a 1009 mb low pressure is located near 31N31W with a trough 
extends from the low pressure to 24N43W. A band of showers  is 
noted well east and southeast of the low and trough axis. 
Satellite-derived wind data show fresh to strong southerly winds 
in the area affected by the convection, mainly N of 23N and 
between 29W and 34W. Low-level convergence is producing an area of
moderate to strong convection from 21N to 23N and between 35W and
40W. Elsewhere in the tropical N Atlantic (aside from near 
Hurricane Sam), fairly tranquil weather conditions and moderate or
weaker winds prevail. Seas of 4-7 ft are prevalent across the 
basin, aside from near Hurricane Sam.

Looking ahead, the surface trough over the west Atlantic will 
dissipate today. Farther east, Hurricane Sam near 13.8N 49.7W 943 
mb at 5 AM EDT moving WNW at 7 kt. Maximum sustained winds 125 kt 
gusts 150 kt. Sam will move to 14.3N 50.6W this afternoon, 15.0N 
51.8W Mon morning, 15.8N 52.9W Mon afternoon, 16.6N 53.9W Tue 
morning, 17.5N 55.0W Tue afternoon, and 18.4N 56.3W Wed morning. 
Sam will change little in intensity as it moves to 20.8N 59.3W by 
early Thu.

$$
ERA