Atlantic Discussions
Basin Outlook & Discussion
ABNT20 KNHC 242312

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 PM EDT Fri Sep 24 2021

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on Hurricane  
Sam, located about 1200 miles east-southeast of the northern 
Leeward Islands, and on newly formed Subtropical Storm Teresa, 
located about 150 miles north of Bermuda.

A tropical wave is expected to move off the west coast of Africa 
early next week.  Thereafter, environmental conditions are 
forecast to be conducive for gradual development, and a tropical 
depression could form by the middle of next week while the system 
moves westward at 10 to 15 mph over the far eastern tropical 
* Formation chance through 48 hours...low...near 0 percent.
* Formation chance through 5 days...medium...50 percent.


Public Advisories on Subtropical Storm Teresa are issued under WMO 
header WTNT34 KNHC and under AWIPS header MIATCPAT4.
Forecast/Advisories on Subtropical Storm Teresa are issued under 
WMO header WTNT24 KNHC and under AWIPS header MIATCMAT4.

Forecaster Berg


AXNT20 KNHC 242335

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0005 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 1800 UTC surface analysis and satellite imagery through 
2220 UTC.


Hurricane Sam is centered near 12.1N 44.8W at 2100 UTC, or about 
1120 nm ESE of the Northern Leeward Islands, moving W at 10 kt. 
Estimated minimum central pressure is 986 mb. Maximum sustained 
wind speed is 75 kt with gusts to 90 kt. Satellite imagery shows 
improving convective structure, with an eye attempting to develop
and well pronounced tightly coiled outer rain bands. Scattered 
strong convection within the central dense overcast feature is 
within 45 nm of center of Sam. Scattered moderate to strong 
convection is with the outer rain bands within 30 nm of a line 
from 11N42W to 13N43W and to 12N45W. Similar convection in another
outer rain band is within 30 nm of a line from 12N46W to 10N44W. 
Peak seas are estimated near 22 ft. A decrease in forward speed 
and a motion toward the west-northwest is expected over the 
weekend. Rapid intensification is forecast to continue, and Sam is
likely to become a major hurricane on Sat. Swell associated with
Sam is expected to reach the Lesser Antilles Sun evening. Please 
read the latest HIGH SEAS FORECAST issued by the National Hurricane
Center at website- 
and the latest Sam NHC Forecast/Advisory and Public Advisory at for more details.

Surface observations and recent satellite imagery indicates that
the low pressure center located 135 nm north of Bermuda has 
become subtropical, and has been classified as Subtropical Storm 
Teresa. Teresa is centered near 34.5N 64.5W at 2100 UTC, moving NW
at 12 kt. Maximum sustained winds are estimated at 40 kt with
gusts to 50 kt, as depicted by late morning ASCAT wind data. 
Estimated minimum central pressure is 1008 mb. Scattered moderate 
isolated strong convection is seen removed from the center, and 
occurring within 180 nm across the N and 360 nm across the NE 
quadrants. Teresa is expected to turn northward on Sat and then 
northeastward, ahead of an extratropical storm system that is 
forecast to develop off of New England this weekend. This will 
allow limited opportunity for Teresa to strengthen slightly during
the next 48 hours before it become absorbed in this developing 
system. Please see the latest High Seas Forecasts issued by the 
Ocean Prediction Center at website for more details on


A far eastern Atlantic tropical wave has its axis along 27W from
04N to 19N, moving westward at 10 kt. Widely scattered moderate 
convection is seen from 03.5N to 11.5N between 21W and 28W. Per 
the latest GOES-16 SAL imagery, the northern part of the wave 
remains embedded in dry Saharan air, inhibiting the development of
shower and thunderstorm activity. 

A central Atlantic tropical wave has its axis near 60W from 07N 
to 19N, moving westward at 10-15 kt. Scattered showers and 
isolated thunderstorms are seen from 11N to 13.5N between 55W and 
60W. Very dry and stable middle level atmospheric conditions
prevail north of 15N across the region, and is limiting 


The monsoon trough axis passes through coast of Senegal near 
13N16.5W to 06.5N28W to 07N33W. A segment of the ITCZ extends 
from 07N46W to 06N53W. Aside from convection associated to the 
tropical waves and Sam described above, scattered moderate
isolated strong convection is seen from 05N to 09N between 30W 
and 45W. 


A quasi-stationary frontal boundary extends from southwestern 
Florida to 23.5N90W and to near Veracruz, Mexico. Satellite 
imagery shows scattered showers and thunderstorms along and within
60 nm either side of the boundary west of 84W. This activity is 
being aided by a mid to upper-level shortwave trough. The air mass
behind the front is quite dry, allowing fairly tranquil weather 
conditions front Texas to Florida in the N Gulf. Recent 
scatterometer satellite data and current buoy observations reveal 
moderate to locally fresh northeast winds behind the front east 
of 91W, and gentle northeast to east winds west of 91W. Light and 
variable winds are south of the frontal boundary. Seas across the 
basin are 3-6 ft, except for slightly lower seas of 1-3 ft over 
the southeastern Gulf.

This quasi-stationary frontal boundary will dissipate by late 
Sat. Moderate to fresh winds prevail north of the front. Winds and
seas will diminish across basin from Sat night and into early 
next week as high pressure builds over the northern Gulf. 


A small upper-level low near the southeastern Bahamas has an
associated trough that reaches to the eastern tip of Cuba and 
to the southwestern Caribbean. A surface trough is analyzed over
the western Caribbean near 86W from 17N-22N. Scattered to numerous 
showers and few thunderstorms prevail across much of the SW
Caribbean, south of 15N and west of 77W to coastal sections of
Nicaragua. Expect for this area to remain convectively active 
through early Sat. Partial ASCAT data passed from this morning 
indicate generally gentle to moderate trades across the basin, 
with the majority of the gentle trades confined to the NW 
Caribbean and to the northern sections of the central and eastern 
Caribbean. Seas across the area remain relatively low, in the 2-3 
ft range, except for slightly higher seas of 4-5 ft over the
waters north of the A-B-C Islands and Gulf of Venezuela.

Hurricane Sam across the central tropical Atlantic will 
strengthen to a major hurricane Sat afternoon near 13N48W and move
to near 15N53W Mon afternoon. Sam is forecast to enter the 
offshore waters east of Leeward Islands Tue near 17N55W and move 
to near 19N58W Wed. 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.


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. Pilots have reported
volcanic ash near Tenerife and over La Gomera. 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 The next advisory 
will be issue no later than 24/2100 UTC.

A cold front extends from near 31N76.5W to 287N78.5W, and 
transitions to a stationary frontal boundary to Stuart, Florida 
and to southwest Florida. A pre-frontal trough is within 30-60 nm 
ahead of the cold front. Scattered moderate to strong convection 
is within 240 nm southeast of the front, from 25N across the
Bahamas northward to 31N. Moderate to fresh southerly winds are 
east of the trough and front to near 75W and north of 26N. Seas 
with these winds are in the 4-6 ft range.

Another area of interest is a sharp surface trough extending from
31N61W to a 1011 mb low near 24N66W. The interaction of these 
features with a large upper-level low near Bermuda is inducing a 
large area of showers and thunderstorms, especially from N of 20N 
and between 56W and 64W. Morning ASCAT wind data indicate fresh 
to strong cyclonic winds near the northern end of the surface 
trough north of 28N. Seas in this region are 5-8 ft. 

Farther east, a 1010 mb low is analyzed near 29N40W. A large area 
of scattered moderate to strong convection is present north 
of 27N between 33W-40W. This convection is shifting eastward.
A stationary front stretches from 31N43W to 29N47W. Scattered 
showers and thunderstorms are along this boundary. Moderate to 
fresh northerly winds were captured by ASCAT off the coast of 
Mauritania, mainly east 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. 

The front across the NW waters to Stuart, 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 will 
strengthen to a major hurricane Sat afternoon near 13N48W and move
to near 15N53W Mon afternoon. Sam will move to near 17N55W Tue 
and to near 19N58W Wed. Swell associated with Sam will reach 55W
early Sun, 60W Sun evening and begin to pass north of the Virgin
Islands and Puerto Rico Mon morning.


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