[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 280541
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0605 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 0000 UTC surface analysis and satellite imagery through
0535 UTC.

...SPECIAL FEATURES...

Hurricane Sam is centered near 16.8N 53.2W at 28/0300 UTC or 575
nm E of the Northern Leeward Islands. It is moving NW at 8 kt.
Estimated minimum central pressure is 956 mb. Maximum sustained
wind speed is 105 kt with gusts to 130 kt. Seas near the center are
currently around 27 ft and are forecast to increase to near 34 ft
by Wednesday. Satellite imagery continues to show a well-defined
eye, although much larger than it was a couple of days ago.
Numerous moderate to scattered strong convection is within 60 nm
of the center in the N and within 60 nm of the center in the S
quadrant. Scattered moderate convection is within 200 nm of the
center in the NE quadrant and within 90 nm in the SW quadrant.
The current NW motion is expected to continue for the next few
days, with an increase in forward speed beginning on Thursday. A
turn to the north is expected by Friday. On the forecast track,
Sam will pass well to the northeast of the northern Leeward
Islands Wednesday and Thursday. The hurricane could strengthen
some overnight, and Sam is anticipated to be a category 3 or 4
hurricane for the next several days. 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. A few
showers and isolated thunderstorms are noted well to the NE of the
center. Although strong upper-level winds are likely to prevent
significant development, this system could still become a short-
lived tropical depression later today or tonight while it moves
northeastward at about 10 mph. By Wednesday, 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 03N to 13N and between 25W and 35W. Environmental conditions are
conducive for further development, and a tropical depression is
likely to form during the next day or two while the system moves
westward to west-northwestward at 5 to 10 mph 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 along 17W, south of 17N and to a 1010 mb low pressure
near 07N17W. This system is producing a large area of disorganized
scattered moderate to isolated strong convection from 03N to 12N
and between 16W and 25W. Upper-level winds are conducive for
gradual development, and a tropical depression is likely to form
in a day or two while the disturbance moves westward to west-
northwestward at 10 to 15 mph 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 the Special Features section for information on the
tropical wave along 17W.

An Atlantic tropical wave has its axis along 33W, south of 17N and
it is moving W at 10-15 kt. The convection near the tropical wave
is likely associated with the broad low pressure discussed in the
Special Features section. The northern portion of the wave is
devoid of deep convection due to the dry Saharan air N of 13N.

Another Atlantic tropical wave has its axis along 43W, south of
17N and it is moving W near 10 kt. A few showers are noted where
the wave interacts with the nearby monsoon trough and ITCZ. The
wave is devoid of deep convection due to the dry Saharan air N of
9N.

A central Caribbean tropical wave has its axis along 76W, south
of 19N and it is moving W near 10 kt. The wave is embedded in a
dry environment, suppressing the development of showers and
thunderstorms.

...MONSOON TROUGH/ITCZ...

A monsoon trough axis enters the Atlantic through the coast of
Senegal near 14N17W to 07N22W to 09N28W to a 1008 mb low pressure
near 08N32W and to 06N40W. An ITCZ segment then extends from 07N44W
to 07N53W. Aside from convection as described above under Special
Features, scattered moderate convection is within 100 nm N of the
ITCZ between 42W to 50W.

...GULF OF MEXICO...

The only feature of interest in the Gulf of Mexico remains a weak
surface trough that is located about 60 nm offshore of Texas and
SW Louisiana, paralleling the coastline. A few showers are
observed near the trough axis. The rest of the Gulf is dominated
by a weak ridge positioned over the SE United States. Moderate to
fresh anticyclonic winds are found in the Florida Straits, in the
E Bay of Campeche and NW Gulf, while gentle to moderate breezes
are noted elsewhere in the basin. Seas of 3-4 ft are occurring in
the Florida Straits, while 1-3 ft are present elsewhere in the
Gulf.

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 toward the end of the week, before
stalling and dissipating over the southeast Gulf by the weekend.
Moderate to locally fresh winds are expected across most of the
Gulf on Fri.

...CARIBBEAN SEA...

Divergence aloft is enhancing the development of showers and
thunderstorms across the north-central Caribbean Sea, especially
in the islands in the region. At this hour, most of the storm
activity is decreasing, but there are still some showers and
isolated thunderstorms in E Cuba and Hispaniola and surrounding
waters. Scattered moderate convection is also seen in the SW
Caribbean, mainly between the island of San Andres and Panama. The
rest of the Caribbean Sea is dominated by dry weather conditions.

A weak pressure gradient across the Caribbean results in moderate
to locally fresh trades, with the strongest winds found within
100 nm of N Colombia and NW Venezuela based on a recent
scatterometer satellite pass. Seas of 3-5 ft are present in the
central and SW Caribbean, while 1-3 ft are occurring in the E
Caribbean and 1-2 ft elsewhere.

For the forecast, Hurricane Sam was near 16.8N 53.2W 956 mb at 11 PM
EDT moving NW at 8 kt. Maximum sustained winds 105 kt gusts 130
kt. Sam will move to 17.5N 54.0W Tue morning, 18.4N 55.1W Tue
evening, 19.3N 56.4W Wed morning, 20.6N 58.0W Wed evening, 22.2N
59.7W Thu morning, and 24.3N 61.0W Thu evening. Sam will change
little in intensity as it moves north of the area late Fri.
Meanwhile, moderate trades will continue over much of the
Caribbean through Tue. 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 and the disturbances in the deep Tropics.

The Cumbre Vieja volcano on the island of La Palma in the Canary
Islands has been erupting since 19/1410 UTC. Volcanic ashes
associated with lava fountains are observed on webcams reaching
3,500 meters. 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/. The
next advisory will be issued no later than 28/0900 UTC.

A cold front enters the W tropical Atlantic near 31N64W and
transitions into a stationary front that stretches to the NW
Bahamas near 25N75W. Scattered moderate convection is observed
near the frontal boundary, mainly from 25N to 28N and between 67W
and 76W. A surface trough extends from a 1012 mb low pressure, the
remnants of Peter, near 32N58W to 24N66W. A few showers and
isolated thunderstorms is noted within 60 nm of the trough axis,
especially near the southern portion. Seas W of 60W are 3-5 ft.

Another feature of interest is a surface trough that extends from
31N28W to 20N36W. Numerous moderate showers and isolated strong
thunderstorms are present within 60 nm of the trough axis. A 1015
mb low pressure, the remnants of Odette, are located near 30N43W
and although the system is devoid of deep convection, satellite-
derived wind data indicate that it is producing fresh breezes
within 120 nm NE of the center. Recent scatterometer data also
show fresh to strong N-NE winds N of 19N and E of 25W, including
the waters surrounding the Canary Islands, with the strongest
winds occurring within 100 nm of the coast of Western Sahara. Seas
in the area of 6-10 ft. Elsewhere in the basin outside of the
influence of Hurricane Sam, winds are moderate or weaker and seas
are 4-8 ft.

For the forecast W of 50W, the aforementioned stationary front is
expected to dissipate tonight. Light to gentle breezes are
expected to prevail with slight seas into mid week west of 65W.
Meanwhile, Hurricane Sam was near 16.8N 53.2W 956 mb at 11 PM EDT
moving NW at 8 kt. Maximum sustained winds 105 kt gusts 130 kt.
Sam will move to 17.5N 54.0W Tue morning, 18.4N 55.1W Tue evening,
19.3N 56.4W Wed morning, 20.6N 58.0W Wed evening, 22.2N 59.7W Thu
morning, and 24.3N 61.0W Thu evening. Sam will change little in
intensity as it moves north of the area, staying east of Bermuda
late 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.

$$
DELGADO
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