[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 271039
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1205 UTC Mon Sep 27 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
1020 UTC.

...SPECIAL FEATURES...

Major Hurricane Sam is centered near 15.2N 51.4W at 27/0900 UTC
or 700 nm ESE of the Northern Leeward Islands moving NW at 7 kt.
Estimated minimum central pressure is 952 mb. Maximum sustained
wind speed is 115 kt with gusts to 140 kt. Peak seas are near 40
ft near the center with 12 ft seas extending 120 nm of the center
except 90 nm in the SE quadrant. Numerous moderate to strong
convection is seen within 90 nm of the center. Scattered moderate
convection is within 150 nm of the center. Sam is moving toward
the northwest, and this general motion is expected to continue
for the next several days, with an increase in forward speed
beginning on Thursday. Little change in strength is expected during
the next day or so. Thereafter, some slow weakening is forecast
through midweek, although Sam should remain a major hurricane. Sam
is expected to pass well NE of the Leeward Islands. Swells
generated by Sam will reach the Lesser Antilles today and impact
these islands for the next several days. These swells could cause
life- threatening surf and rip current conditions. 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.

Satellite-derived wind data indicate an elongated area of low pressure
associated with the remnants of Peter is located a few hundred
miles southeast of Bermuda. Showers and thunderstorms have become
a little better organized since last night, and environmental
conditions are marginally conducive for some further development
of this system. Peter could briefly become a tropical depression
again during the next day or two while it moves northeastward at
about 10 mph. By midweek, environmental conditions are expected to
become unfavorable for further development. This disturbance has
a medium chance of development over the next 48 hours. Please
visit hurricanes.gov for more details.

...TROPICAL WAVES...

An Atlantic tropical wave has its axis along 30W, south of 17N,
and it is moving W near 15 kt. Interaction between the wave and
the monsoon trough allows for scattered moderate to isolated
strong convection from 03N to 10N and between 28W and 32W. The
northern portion of the wave is devoid of deep convection.

Another Atlantic tropical wave has its axis along 40W, south of
16N and it is moving W at 10-15 kt. Interaction between the wave
and the monsoon trough results in scattered moderate convection E
of the wave axis to 30W and between 04N and 11N. The northern
portion of the wave is devoid of deep convection.

A Caribbean tropical wave has its axis along 73W, south of 19N,
extending from Haiti to Colombia and it is moving W near 10 kt.
The wave is enhancing the thunderstorm activity over Hispaniola.
No deep convection is noted near the wave axis over the Caribbean
Sea.

...MONSOON TROUGH/ITCZ...

The monsoon trough enters the Atlantic through the coast of The
Gambia/Senegal near 13N17W to 08N20W to 09N32W and to 07N43W.
There is no ITCZ at this time. Scattered moderate to strong
convection is observed south of the monsoon trough from 01N to
09N and east of 24W to the coast of Africa.

The E Pacific monsoon trough enters the Caribbean Sea through the
coast of Costa Rica near 11N83W and continues to the coast of NW
Colombia. Scattered moderate to isolated strong is S of 13N
between 78W to 84W.

...GULF OF MEXICO...

A tenacious surface trough remains in the W Gulf, extending from
28N90W to 23N96. Showers and thunderstorms continue to flare up
near the trough axis. A few showers and isolated thunderstorms
are also noted over the E Bay of Campeche and off W Florida.
However, this activity is quickly losing strength and should
dissipate soon. The rest of the basin is under the dominance of
dry air, leading to fairly tranquil weather conditions. An
overnight scatterometer satellite pass indicated fresh NE winds
in the Florida Straits, while gentle to moderate anticyclonic
winds prevail in the remainder of the Gulf. Seas in the SE Gulf
are 2-4 ft, with the highest seas occurring in the Florida
Straits. Elsewhere, seas are 1-3 ft.

The aforementioned surface trough will continue to drift westward
toward the Texas coast through tonight. High pressure presently
over the area will remain in place trough Thu, then be replaced by
slighter stronger high pressure that will build southward over
the area Fri and Fri night. This will bring moderate to fresh
winds over most of the Gulf on Fri through Sat..

...CARIBBEAN SEA...

Favorable upper-level atmospheric dynamics and diurnal heating in
the northern Caribbean allowed for the development of afternoon
and evening thunderstorms across the Greater Antilles. A few
showers and thunderstorms are seen in the E Caribbean, near the
Lesser Antilles with isolated thunderstorms in the NW Caribbean.
while fairly tranquil conditions prevail in the rest of the basin.
Overnight satellite- derived wind data show fresh trades within
100 nm of the coast of Colombia and NW Venezuela, including the
waters surrounding the ABC islands. Moderate to locally fresh
trades are present elsewhere in the Caribbean Sea. Sea of 3-6 ft
are occurring in the central Caribbean, with the highest seas
materializing in the south- central and SW Caribbean. Elsewhere,
seas are 1-3 ft.

Hurricane Sam was near 15.2N 51.4W 952 mb at 5 AM EDT
moving NW at 7 kt. Maximum sustained winds 115 kt gusts 140 kt.
Sam will move to 15.9N 52.2W this afternoon, 16.8N 53.3W Tue
morning, 17.7N 54.4W Tue afternoon, 18.6N 55.6W Wed morning, 19.6N
57.1W Wed afternoon, and 21.0N 58.8W Thu morning. Sam will change
little in intensity as it moves near 24.9N 61.6W early Fri.
Meanwhile, moderate trades will continue over much of the
Caribbean through Tue. Fresh trades over the south- central
Caribbean will diminish to gentle to moderate speeds today. Gentle
trades will then prevail over the Caribbean through Fri. Fresh
trades will follow in the wake of Sam across the Tropical N
Atlantic waters. Swells generated by Sam are forecast to reach the
Lesser Antilles by later today through the middle of the week.

...ATLANTIC OCEAN...

Please read the Special Features section above for details on
Hurricane Sam.

The Cumbre Vieja volcano on the island of La Palma in the Canary
Islands has been erupting since 19/1410 UTC. Significant
volcanic ash is mainly in the vicinity of the volcano below 5000
ft. ANother cloud mainly composed of SO2 is drifting to the NE.
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 27/1500 UTC.

A cold front traversing the NW Atlantic enters the tropical
Atlantic near 31N68W and extends to 28N77W, about 100 nm NE of
the NW Bahamas. A pre-frontal trough is analyzed from 29N68W to
25N74W. Scattered moderate convection is noted from 24N to 30N
between 66W and 75W. Satellite- derived wind data depict moderate
to fresh cyclonic winds surrounding the trough, with the highest
winds occurring near the convection.

Farther east, a cold front extends from a 1013 mb low pressure SW
of the Azores and enters the tropical Atlantic near 31N28W and
transitions into a stationary front that extends from 28N30W to
22N46W. Showers and thunderstorms are noted along this boundary
from 19N to 30N between 25W and 37W. Overnight satellite- derived
wind data indicated that fresh to strong southerly winds are
occurring N of 25N and within 150 nm to the E of the frontal
boundary. The scatterometer satellite data also depicted fresh to
locally strong NE winds N of 22N and E of 20W, with the strongest
winds occurring near the coast of NW Africa. Outside of the
influence of Hurricane Sam, the rest of the basin experiences
moderate or weaker winds. Seas are 4-8 ft with the highest seas
occurring near the areas described above.

A cold front is pressing southward across the Bahamas with a
trough stretching from 30N68W to 25N74W. This front will weaken by
tonight. Expect showers and thunderstorms along this boundary
through Mon night. Gentle to moderate winds will prevail through
most of the week. Stronger high pressure will build southward over
the NW and north- central offshore waters late in the week,
bringing moderate to locally fresh winds across the northern SW
Atlantic. Meanwhile, Hurricane Sam was near 15.2N 51.4W 952 mb at
5 AM EDT moving NW at 7 kt. Maximum sustained winds 115 kt gusts
140 kt. Sam is forecast to continue on its current motion over the
next few days as it slowly weakens reaching near 25N62W by late
Fri, with maximum sustained winds 105 kt gusts 130 kt. Swells
generated by Sam are expected to spread westward across the
forecast waters late in the week.

$$
AReinhart
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