[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 271807
TWDAT

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

...SPECIAL FEATURES...

Major Hurricane Sam is centered near 15.7N 52.1W at 27/1500 UTC
or 645 nm ESE of the Northern Leeward Islands, and moving NW at 7
kt. Estimated minimum central pressure is 966 mb. Maximum
sustained winds are 110 kt with gusts to 135 kt. Seas are peaking
from 28 to 30 ft within 50 nm the center, and ranging between 15
and 25 ft farther out to 100 nm in a northern semicircle; and out
to 60 nm in a southern semicircle. Numerous moderate to scattered
strong convection is seen near the center from 14N to 16N between
51W and 52W. Scattered moderate convection is evident farther N
and NE from 16N to 18N between 49W and 53W. This NW motion is
expected to continue through Thu with an increase in forward speed
starting Wed night. Sam will pass well NE of the Northern Leeward
Islands Wed, then Puerto Rico on Thu. Slight fluctuation in
strength is possible but Sam should remain a major hurricane
through Thu. Swells generated by Sam will reach the Lesser
Antilles today and impact these islands at least through midweek.
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://nhc.noaa.gov/cyclones/

An elongated area of low pressure associated with the remnants of
Peter is located a few hundred miles east-southeast of Bermuda.
Showers and thunderstorms associated with this system have changed
little in organization since yesterday. However, environmental
conditions are marginally conducive for some further development,
and Peter could briefly become a tropical depression again during
the next day or two while it moves northeastward near 10 mph.
There is a medium chance of development for the next 48 hours.

Disorganized showers and thunderstorms are associated with a broad
area of low pressure located several hundred miles SW of the Cabo
Verde Islands. Environmental conditions are forecast to be
conducive for further development of this disturbance, and a
tropical depression is likely to form in a few days while it moves
W to WNW at 5 to 10 mph over the central tropical Atlantic. There
is a medium chance of development for the next 48 hours.

A tropical wave is near the coast of Senegal and just offshore
from Sierra Leone in W Africa. Upper-level winds are forecast to
be conducive for gradual development, and a tropical depression is
likely to form in a few days while the system moves W to WNW at
10 to 15 mph over the far eastern tropical Atlantic. There is a
medium chance of development for the next 48 hours.

Please read the latest Tropical Weather Outlook at
https://nhc.noaa.gov/gtwo.php?basin=atlc&fdays=2 for more details
on all three disturbances.

...TROPICAL WAVES...

A newly analyzed Atlantic tropical wave is near 16W from the
Senegal coast at 16N southward through a low pressure offshore of
Sierra Leone, and moving W at 5 to 10 kt. Scattered moderate to
isolated strong convection is found from 03N to 08N between the
Sierra Leone-Liberia coast and 20W.

An Atlantic tropical wave is along 31W from 17N southward and moving
W near 15 kt. Scattered moderate to isolated strong convection is
present from 03N to 12N between 28W and 36W.

Another Atlantic tropical wave is near 41W from 16N southward and
moving W near 10 kt. Scattered moderate convection is found from
06N to 10N between 36W and 41W.

A Caribbean tropical wave is along 74W from W Hispaniola
southward to N Colombia, and moving W at 5 to 10 kt. Scattered
showers and thunderstorms are occurring over central Hispaniola
and near the Colombia-Venezuela border.

...MONSOON TROUGH/ITCZ...

A monsoon trough enters the Atlantic through the coast of Senegal
near 14N17W to 08N25W to 08N39W. Scattered moderate to isolated
strong convection is observed near and S of the monsoon trough
from 02N to 09N between 20W and 28W. No ITCZ is present based on
the latest analysis.

The eastern end of the E Pacific monsoon trough is triggering
numerous heavy showers and scattered thunderstorms over the SW
corner of the Caribbean Sea, including the coast of Nicaragua,
Costa Rica and W Panama.

...GULF OF MEXICO...

A surface trough remains in the NW Gulf just off the Texas-
Louisiana coast. This feature is producing scattered showers and
isolated thunderstorms over the NW and N central Gulf. Otherwise,
a broad surface ridge extending southwestward from the mid-
Atlantic US States to central Mexico is dominating much of the
Gulf with light to gentle winds and seas of 2 to 3 ft.

For the forecast, the surface trough will drift westward toward
the Texas coast through tonight. High pressure will persist across
the E and central Gulf through mid week. A weak cold front will
move into the E Gulf Thu night through Fri.

...CARIBBEAN SEA...

Convergent trades are coupling with a mid-level trough to cause
scattered showers and thunderstorms across W and central Cuba. An
upper-level low W of the Lesser Antilles near 14N65W is inducing
scattered showers and isolated thunderstorms over the SE corner of
the basin, including the Windward Islands. Refer to the Tropical
Waves and Monsoon Trough/ITCZ sections for additional convection
in the basin. Moderate to fresh ENE trades and seas at 4 to 6 ft
are evident across the central and S central basin. Light to
gentle trades and seas of 2 to 3 ft prevail for the rest of the
basin.

For the forecast, Hurricane Sam will continue on a NW course and
pass well NE of the Lesser Antilles Tue and Wed. Swell generated
by it will maintain higher seas near the Leeward Islands through
Fri, and near Puerto Rico by Wed. Meanwhile, moderate trades will
continue over much of the Caribbean through Tue. Fresh trades
over the S central Caribbean will diminish to gentle to moderate
speeds today. Gentle trades will then prevail over the Caribbean
through Fri.

...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 6000
ft. 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 27/2100 UTC.

A cold front enters the NW corner of the tropical Atlantic at
30N66W, then curves southwestward to the NW Bahamas. Scattered
showers and isolated thunderstorms are found up to 100 nm NW, and
up to 80 nm SE of this front. A weakening frontal boundary
extends southwestward from NW of the Canary Islands across 31N28W
through a low pressure near 22N36W then turns westward to 22N46W.
Similar conditions exist up to 80 nm on neither side of this
boundary N of 22N.

A surface trough reaches northeastward from the central Bahamas
to just S of the aforementioned cold front at 28N70W. Scattered
showers and thunderstorms are flaring up from the N coast of Cuba
across the central Bahamas to NE of the SE Bahamas. Another
surface trough curves southwestward from the remnant of Peter near
31N59W to well N of Puerto Rico at 24N66W. Scattered showers and
thunderstorms are occurring N of 25N between 57W and 63W.

Refer to the Tropical Waves and Monsoon Trough/ITCZ sections for
additional convection across the basin. Light to gentle winds and
seas at 3 to 5 ft are evident N of 20N between 28W and the 64W.
N of 20N, moderate to locally fresh winds and seas of 4 to 7 ft
are seen 64W and the Georgia-Florida coast, and also between the
NW African coast and 28W; including the Canary Islands. Outside
the influence of Hurricane Sam, gentle to moderate trades and seas
at 5 to 6 ft are found from 10N to 20N between the African coast
and the Less Antilles. Gentle to locally moderate monsoonal winds
and seas of 4 to 7 ft prevail for the remainder of the basin.

For the forecast W of 45W, a cold front extending from 30N65W to
Grand Bahama Island will stall late today and dissipate through
tonight, leaving generally light to gentle breezes and slight seas
into mid week W of 65W. Meanwhile, Hurricane Sam will move to
16.4N 52.8W this evening, 17.3N 53.9W Tue morning, 18.1N 55.1W Tue
evening, then move to northeast of the Leeward Islands to 19.1N
56.5W by Wed morning. Sam will continue to the northwest reaching
20.2N 58.1W Wed evening, and 21.7N 59.8W Thu morning. Sam will
change little in intensity as it moves more northward to southeast
of Bermuda through Fri. At a minimum, expect rough seas in the
outer swell from Sam from mid to late week, reaching as far west
as 70W by Thu.

$$

Chan
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