[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 280005
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0005 UTC Tue Sep 28 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
2345 UTC.

...SPECIAL FEATURES...

Major Hurricane Sam is centered near 16.3N 52.7W at 27/2100 UTC
or 610 nm E of the Northern Leeward Islands. It is moving NW at
8 kt. Estimated minimum central pressure is 957 mb. Maximum
sustained wind speed is 105 kt with gusts to 130 kt. Seas are
peaking to a range of 29-33 ft within 50 nm the center, and
ranging between 15 and 25 ft farther out to 100 nm in a northern
semicircle nd out to 60 nm in a southern semicircle. Satellite
imagery shows that an eye feature has become visible once again.
Numerous moderate to scattered strong convection is within 90 nm
of the center in the NE and within 60 nm of the center in the
SE quadrant. Scattered moderate convection is within 120 nm of
the center in the SW and within 150 nm in the NW quadrant.
The present NW motion is forecast to continue for the next few
days, with an increase in forward speed beginning on Thu. A turn
to the north is expected by Fri. On the forecast track, Sam will
pass well to the northeast of the northern Leeward Islands
Wed and Thu. Some strengthening is expected through tonight.
Thereafter, fluctuations in intensity are possible through
Thu. Swells generated by Sam will impact the Lesser Antilles for
the next several days.  Swells are expected to reach Bermuda and
the Bahamas mid-to-late week, and then spread to the United
States east coast late this week. 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/

A well-defined low pressure system associated with the remnants
of Peter is located a few hundred miles east of Bermuda. Although
scattered moderate convection to northeast of the low center
from 32N to 33N between 56W-58W is currently disorganized,
environmental conditions are expected to remain marginally
conducive for a short-lived tropical depression to form tonight
or Tue while the system moves northeastward at about 10 mph. By
Wed, however, conditions are expected to become unfavorable for
further development. This system has a medium chance of
development during the next 48 hours. Please refer to the latest
NHC Tropical Weather Outlook at www.hurricanes.gov for more
details.

A broad area of low pressure located several hundred miles
southwest of the Cabo Verde Islands is producing a large area
of disorganized scattered moderate to isolated strong convection
from 04N to 11N between 20W-30W. Environmental conditions are
conducive for further development of this disturbance, and a
tropical depression is likely to form during the next day or two
while the system moves westward to west-northwestward near 8 kt
over the central tropical Atlantic. This system has a high
chance of development during the next 48 hours. Please refer to
the latest NHC Tropical Weather Outlook at www.hurricanes.gov for
more details.

A far eastern Atlantic tropical wave just offshore the west
coast of Africa extends from 16N17W to a 1010 low near 07N17W and
to 04N12N. This system is producing a large area of disorganized
scattered moderate to isolated strong convection from 04N to 08N
between 15W-20W. Upper-level winds are conducive for gradual
development, and a tropical depression is likely to form in a
couple of days while the system moves westward to west-
northwestward at 8 to 13 kt over the far eastern tropical
Atlantic. This system has a high chance of development during
the next 48 hours. Please refer to the latest NHC Tropical
Weather Outlook at www.hurricanes.gov for more details.

...TROPICAL WAVES...

Please see above for information on a far eastern Atlantic
Special Feature tropical wave along 16W/17W.

An eastern Atlantic tropical wave has its axis along 32W from
04N to 17N, moving westward near 15 kt. Scattered moderate to
isolated strong convection is within 180 nm east of the wave
from 10N to 11N and within 120 nm east of the wave from 04N to
07N. Scattered moderate convection is within 180 nm west of the
wave from 09N to 11N.

A central Atlantic tropical wave has its axis along 42W from
03N to 16N. It is moving westward at 10-15 kt. Isolated moderate
convection is within 120 nm west of the wave from 08N to
09N and within 60 nm east of the wave from 08N to 09N.

A central Caribbean tropical wave has its axis along 75W south
of 19N to inland northwest Colombia. It is moving westward
near 10 kt. No significant conveciton is noted with this wave
over the Caribbean. Scattered moderate convection is within
30 nm of the wave axis over Colombia from 08N to 10N.

...MONSOON TROUGH/ITCZ...

A monsoon trough axis enters the Atlantic through the coast of
Senegal near 14N17W to 08N24W and to 08N40W. An ITCZ segment
begins at 08N43W to 07N50W. Aside from convection as described
above under Special Features, scattered moderate convection is
within 60 nm north of the ITCZ between 46W-50W.

...GULF OF MEXICO...

A surface trough remains in the NW Gulf just off the Texas-
Louisiana coasts. This feature is producing scattered showers
and isolated thunderstorms over the NW and north-central Gulf
waters. 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 trough will drift westward toward the
Texas coast through tonight. High pressure will persist across
the eastern and central Gulf through mid week. A weak cold front
will move into the eastern Gulf Thu night through Fri, before
stalling and dissipating over the southeast Gulf by Sat.

...CARIBBEAN SEA...

An upper-level low over the eastern Caribbean near 14N66W is
producing isolated showers and thunderstorms over the southeast
part of the basin. Moderate to fresh northeast to east trades
along with seas of 4 to 6 ft are evident across the central and
south- central sections of the basin. Light to gentle trades and
seas of 2 to 3 ft prevail for the rest of the basin.

The eastern end of the E Pacific monsoon trough is triggering
numerous moderate to strong convection over the far southwest
part of the sea south of 13N and west of 79W. The southern part
of an upper-level trough over the northwest Caribbean is aiding
this convection. Similar convection is over Panama and southern
Costa Rica.

Scattered moderate to isolated strong convection is over the
interior sections of the Dominican Republic.

For the forecast, Hurricane Sam was near 16.3N 52.7W 957 mb at
2100 UTC, moving NW at 8 kt. Maximum sustained winds are 105 kt,
with gusts to 130 kt. Sam will move to 17.0N 53.5W Tue morning,
17.8N 54.6W Tue afternoon, 18.8N 55.8W Wed morning, 19.8N 57.3W
Wed afternoon, 21.2N 59.0W Thu morning, and 22.9N 60.5W Thu
afternoon. Sam will change little in intensity as it continues to
move north of the area through 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. Swells generated by Sam are forecast
to continue off the Leeward Islands 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 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 28/0300 UTC.

A cold front extends from 31N65W to 27N71W and 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 extends from 25N65W to low pressure, remnants
of Peter, near 31N59W 1010 mb. Scattered moderate convection is
within 60 nm of 25N65W and within 30 nm east of the trough
from 27N-29N.

An eastern 1015 mb low is located near 23N36W, with a trough to
21N41W and to 22N46W, and another trough northeast from the low
to 29N29W. Scattered moderate convection is within 120 nm of
the low in the NE quadrant, and within 30 nm of the trough
between 32W-33W.

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, the cold front that extends from
31N65W to 27N71W and to the NW Bahamas will stall this evening
and dissipate overnight, leaving generally light to gentle
breezes and slight seas into mid week west of 65W. Meanwhile,
Hurricane Sam was near 16.3N 52.7W 957 mb at 21 UTC, moving NW at
8 kt. Maximum sustained winds are 105 kt, with gusts to 130 kt.
Sam will move to 17.0N 53.5W Tue morning, 17.8N 54.6W Tue
afternoon, then to northeast of the Leeward Islands near 18.8N
55.8W by early Wed morning. Sam will continue to move northwest
to 19.8N 57.3W Wed afternoon, 21.2N 59.0W Thu morning, and 22.9N
60.5W Thu afternoon. Sam will change little in intensity as it
moves 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 late Thu.

$$
Aguirre
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