[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 291805
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1805 UTC Wed Sep 29 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 1200 UTC surface analysis and satellite imagery through
1530 UTC.

...SPECIAL FEATURES...

Hurricane Sam was centered near 19.4N 57.0W at 29/1500 UTC or 350
nm ENE of the Northern Leeward Islands, and moving NW at 8 kt.
Estimated minimum central pressure is 949 mb. Maximum sustained
winds are 115 kt with gusts to 140 kt. Seas are peaking at 27 to
29 ft near and up to 60 nm N of the center, while the 15 to 25 ft
seas extend farther out up to 100 nm away from the center. Latest
satellite imagery shows a cloud-filled eye about 15 nm in
diameter. Numerous strong convection is within 90 nm of the center
in the NE semicircle and within 50 nm of the center in the SW
semicircle. Scattered moderate convection is seem farther N from
21N to 22N between 55W and 58W, and farther SE from 18N to 21N
between 54W and 56W. Sam will continue moving NW with a gradual
increase in forward speed through Thu morning. Then a turn toward
the NNE is expected Thu night and Friday. On the forecast track,
Sam will pass well NE of the Northern Leeward Islands tonight, and
then well NE of Puerto Rico Thu. Some fluctuations in intensity
are expected during the next couple of days, but Sam is forecast
to remain a major hurricane through late this week. Swells
generated by Sam will continue to impact the Leeward Islands for
the next few days, and reach Puerto Rico and the Virgin Islands
early Thu morning. These swells are expected to reach Bermuda and
the Bahamas in a day or two, and then spread to the United States
east coast by this weekend. These swells could cause life-
threatening surf and rip current conditions. Please read the
latest High Seas Forecast issued by the National Hurricane Center
at website https://www.nhc.noaa.gov/text/MIAHSFAT2.shtml and the
latest NHC Forecast/Advisory and Public Advisory at
www.hurricanes.gov for more details.

Newly formed Tropical Depression (TD) Twenty was centered near
8.3N 24.6W at 29/1500 UTC or 465 nm S of the Cabo Verde Islands,
and moving WNW at 12 kt. Estimated minimum central pressure is
1007 mb. Maximum sustained winds are 30 kt with gusts to 40 kt.
Seas are peaking at 20 to 22 ft near the center. An area of fresh
to strong winds and seas at 8 to 10 ft are found S of the center
from 04N to 07N between 18W and 26W, and also N of the center from
09N to 12N between 19W and 26W. Numerous moderate to isolated
strong convection is evident up to 200 nm in a NW semicircle from
the center. Scattered moderate convection is seen up to 190 nm in
a SE semicircle from the center. TD Twenty will continue on a WNW
course for the next several days with a slight increase in forward
speed on Thu afternoon, staying away from the Cabo Verde Islands.
TD Twenty is expected to strengthen steadily and will likely
become a tropical storm later tonight, and possibly a hurricane in
a couple of days. Please read the latest High Seas Forecast
issued by Meteo-France at website
https://www.weather.gmdss.org/II.html and the latest NHC
Forecast/Advisory and Public Advisory at www.hurricanes.gov for
more details.

...TROPICAL WAVES...

An Atlantic tropical wave is along 41W from 17N southward and
moving W near 10 kt. Scattered moderate convection is found from
06N to 10N between 40W and 43W.

A western Caribbean tropical wave is near 82W from 18N southward
across W Panama into the E Pacific Ocean, and moving W at 5 to 10
kt. Scattered moderate to isolated strong convection is present
over the SW corner of the Caribbean Basin.

...MONSOON TROUGH/ITCZ...

A monsoon trough enters the Atlantic through the coast of
Mauritania near 18N16W through newly formed Tropical Depression
Twenty, and a 1009 mb low near 07N33W to 06N40W. Farther W, the
ITCZ extends from 05N43W to 07N52W, N of the French Guiana-Brazil
border. Scattered moderate to isolated strong convection is
present near the low and monsoon trough from 04N to 11N between
30W and 40W. Scattered moderate convection is found well S of the
monsoon trough from 02N to 08N between the African coast and 18W,
and also near up to 60 nm on neither side of the ITCZ.

...GULF OF MEXICO...

A 1009 mb low over SE Texas is coupling with strong divergent
winds aloft to trigger numerous heavy showers and scattered
thunderstorms over the NW and N central Gulf, including the Texas
and Louisiana coastline. Moderate to locally fresh winds and seas
up to 5 ft are possible near these showers and thunderstorms.
Otherwise, a broad surface ridge extending southwestward from N
Florida to central Mexico should sustain light to gentle winds and
seas at 1 to 3 ft across the E and central Gulf. Moderate SE to S
winds and seas of 2 to 4 ft prevail across the rest of the Gulf,
including the Yucatan Channel.

For the forecast, weak high pressure will stay in place over Gulf
through Fri. Moderate to locally fresh southerly winds are
expected in the W Gulf through Thu with gentle winds in the
E Gulf. A weak cold front will press southward over the E Gulf on
Fri and weaken by Sat. Stronger higher pressure will build across
the region through Sat. Moderate to fresh winds are expected to
prevail in the E Gulf with gentle to moderate winds in the
W Gulf through the weekend.

...CARIBBEAN SEA...

Light easterly trade winds allow island heating to generate
isolated thunderstorms over Hispaniola and Puerto Rico. Farther
S, convergent trades are causing scattered showers and
thunderstorms near the Colombia-Venezuela border and adjacent
waters, and also over NE Venezuela and nearby waters. Refer to the
Tropical Waves section for additional convection in the basin.
Light to gentle trades and seas of 2 to 3 prevail across the
entire Caribbean Basin.

For the forecast, Hurricane Sam is going to pass well NE of the
Northern Leeward Islands tonight, and then Pareto Rico Thu.
Swells generated by Sam are forecast to continue off the Leeward
Islands through Thu and will begin to impact the Mona and Anegada
Passages later today through Fri. Meanwhile, gentle trades will
prevail over the Caribbean through Fri. Winds are expected to
increase moderate to fresh across the basin by the weekend.

...ATLANTIC OCEAN...

Please read the Special Features section above for details on
Hurricane Sam and newly formed Tropical Depression Twenty.

The Cumbre Vieja volcano on the island of La Palma in the Canary
Islands near 28.6N 17.8W has been erupting since September 19th.
High concentration of volcanic ash is found near the volcano up
to 11,500 ft or 3,500 m ASL. Marine and aviation interests should
monitor this ongoing situation by reading Volcanic Ash Advisory
issued by Meteo-France at http://vaac.meteo.fr/volcanoes /la-
palma/ for details. The next advisory will be issued no later than
29/2100 UTC.

A surface trough meanders east-northeastward from near the central
Bahamas to SE of Bermuda at 31N59W. Scattered showers and isolated
thunderstorms are occurring up to 180 nm on neither side of this
feature, including the NW and central Bahamas. Refer to the
Tropical Waves and Monsoon Trough/ITCZ sections for additional
convection across the Atlantic Basin. Light to gentle with locally
moderate winds and seas of 2 to 4 ft are evident N of 24N between
33W and the Georgia-Florida coast. Fresh to strong with locally
near-gale NE trades and seas at 8 to 12 ft exist N of 19N between
the NW African coast and 33W. Outside the influence of Hurricane
Sam, gentle to moderate trades and seas of 4 to 6 ft are found
from the Equator to 24N between 35W and the Lesser Antilles.
Outside the influence of Tropical Depression Twenty, gentle to
moderate monsoonal winds and seas at 5 to 7 ft prevail across the
rest of the basin.

For the forecast, Hurricane Sam was near 19.4N 57.0W 949 mb at
29/1500 UTC, and moving NW at 8 kt. Maximum sustained winds are
115 kt with gusts 140 kt. Sam will move to 20.3N 58.1W this
evening, 21.8N 59.6W Thu morning, 23.9N 61.0W Thu evening, 26.6N
61.8W Fri morning, and 29.4N 61.8W Fri evening. Sam will change
little in intensity as it moves into the N central Atlantic into
Sun. In addition to hurricane conditions northeast of the Leeward
Islands through today, expect rough seas in the form of swell from
Sam to impact the area NE of the Bahamas by Thu. Farther west, a
weak pressure pattern will maintain light to gentle breezes and
slight seas through Thu. A weak cold front will move from the
Carolinas to the central Bahamas by Fri and and dissipate by Sat.
Stronger high pressure will build into the area, which will bring
moderate to fresh winds through the weekend.

$$

Chan
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