[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 250507
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0605 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 0000 UTC surface analysis and satellite imagery through
0505 UTC.

...SPECIAL FEATURES...

Hurricane Sam continues to gain strength over the central
Atlantic. It is centered near 12.4N 45.9W at 0300 UTC, or about
1055 nm ESE of the Northern Leeward Islands, moving WNW at 12 kt.
Estimated minimum central pressure is 982 mb. Maximum sustained
wind speed is 85 kt with gusts to 100 kt. The appearance
continues to improve as an eye becomes better defined on infrared
satellite imagery. Numerous moderate to strong convection within
about 40 nm of the center. Scattered moderate to strong convection
is elsewhere in bands within 130 nm E and 80 nm E semicircles,
making Sam a very compact hurricane. Peak seas near the center are
estimated near 25 ft and expected to reach 30 ft by Sunday
morning. A motion toward the west or west-northwest with a
decrease in forward speed is expected over the weekend. A turn
toward the northwest is forecast on Monday. Additional
strengthening is forecast, and Sam is expected to become a major
hurricane on Saturday. Swell associated with Sam is expected to
reach the Lesser Antilles Sunday evening. Please read the latest
HIGH SEAS FORECAST issued by the National Hurricane Center at
https://www.nhc.noaa.gov/text/MIAHSFAT2.shtml and the latest NHC
Forecast/Advisory and Public Advisory on Sam at
www.hurricanes.gov for more details.

Subtropical Storm Teresa is centered near 34.3N 65.4W at 0300
UTC, moving WNW at 9 kt. Estimated minimum central pressure is 1008
mb. Maximum sustained wind speed is 40 kt with gusts to 50 kt. The
center of Teresa is devoid of deep convection. 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. The storm is moving toward the west-northwest and a
turn toward the north and northeast is expected during the next
day or two. Little change in strength is forecast during the next
36 hours. Teresa is expected to be short-lived and should
dissipate in about two days. 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 29W, 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 61W, south of 20N, and it is
moving W near 15 kt. A few showers are observed near the wave
axis.

...MONSOON TROUGH/ITCZ...

The monsoon trough axis passes through coast of Senegal near
13N16W to 08N25W and to 06N32W. A segment of the ITCZ extends
from 06N33W to 07N40W and another segment continues from 06N48W to
06N53W. Aside from convection associated to the tropical waves
and Sam described above, isolated moderate convection is noted
from 04N to 10N and between 30W to 45W. Another area of scattered
moderate convection is seen south of the Cabo Verde Islands from
10N to 12N and between 20W to 25W.

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 locally 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 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.

CARIBBEAN SEA...

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, but
only a few shallow showers are near this feature. The surface
trough is quite evident in a recent scatterometer satellite pass,
showing broad troughiness over the Gulf of Honduras. A few
showers are also observed in the E Caribbean, near the Lesser
Antilles, due to moisture associated with a tropical wave entering
the region. 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 are 1-3 ft.

For the forecast, Hurricane Sam near 12.4N 45.9W 982 mb at 11 PM EDT
moving WNW at 12 kt. Maximum sustained winds 85 kt gusts 105 kt.
Sam will move to 12.7N 47.4W Sat morning, 13.1N 48.8W Sat
evening, 13.5N 50.0W Sun morning, 14.1N 51.2W Sun evening, 14.8N
52.4W Mon morning, and 15.7N 53.5W Mon evening. Sam will change
little in intensity as it moves to 17.4N 55.8W by late 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.

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 25/0900 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 tough
is analyzed from 31N74W to SW Florida. Scattered moderate to
isolated strong convection is observed on infrared satellite
imagery from 23N to 30N 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 30N61W to the 1011 mb
remnant low of Peter near 24N65W to 20N66W. The interaction of
these features with an upper level trough to the north results in
a large area of showers and thunderstorms from 22N to 30N and
between 58W and 64W. 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, latest scatterometer satellite data indicate that
the the remnant low of Rose has weakened into a sharp surface
trough, extending from 31N38W to 26N40W. In the vicinity of this
feature is a stationary front that stretches from 31N40W to
28N47W. An upper level trough nearby is interacting with these
features, inducing a large area of scattered moderate to isolated
strong convection N of 27N and between 32W and 40W. Satellite-
derived wind data depict fresh to strong southerly winds N of 25N
and between 36W and 40W, likely associated with the convection.
Two other surface troughs traverse the Atlantic, one stretches
from 22N53W to 18N54W and the other one along 30W from 26N to 31N.
Neither of these features is producing deep 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 is near 12.4N 45.9W 982 mb at 11 PM EDT, moving WNW
at 12 kt. Maximum sustained winds 85 kt gusts 105 kt. Sam will
strengthen to a major hurricane on Sat near 12N47W and move to
near 13.5N50.0W Sun morning, 14.1N 51.2W Sun evening, 14.8N52.4W
Mon morning, and 15.7N53.5W Mon evening. Sam will change little in
intensity as it moves to 17.4N55.8W by late Tue.

$$
DELGADO
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