[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 281039
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1205 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 0600 UTC surface analysis and satellite imagery through
1030 UTC.

...SPECIAL FEATURES...

Hurricane Sam was centered near 17.2N 53.9W at 28/0900 UTC or 530
nm E of the Northern Leeward Islands moving NW at 8 kt. Estimated
minimum central pressure is 953 mb. Maximum sustained wind speed
is 115 kt with gusts to 140 kt. Peak seas near the center are
currently around 30 ft and are forecast to increase to near 38 ft
by Thu. Satellite imagery continues to show a well-defined eye.
Numerous moderate to scattered strong convection is within 100 nm
of the center in the E and within 60 nm of the center in the W
quadrant. Scattered moderate convection is within 150 nm of the
center. Sam is moving toward the northwest and is expected to
continue for the next few days, with an increase in forward speed
beginning on Thursday. A turn toward the north is expected by
Friday. On the forecast track, Sam will pass well to the northeast
of the northern Leeward Islands on Wednesday and Thursday. 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 impact the Lesser
Antilles for the next several days. Swells are expected to reach
Bermuda and the Bahamas within a couple of days, 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 showers and thunderstorms. 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 10 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 located over the far eastern
tropical Atlantic several hundred miles southeast of the Cabo
Verde Islands continues to produce a large area of disorganized
showers and thunderstorms. 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 10-15 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.

A well-defined low pressure area associated with the remnants
of Peter is located a few hundred miles east of Bermuda. The shower
and thunderstorm activity associated with this system has become
less organized since early Monday.  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 in 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 35W, 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 45W, south of
16N 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 77W, 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 15N17W to 08N22W to a 1010 mb low near 08N33W to
05N39W. The ITCZ extends from 05N39W to 05N44W, then begins W of a
tropical wave near 05N45W to 06N53W. Aside from convection as
described above under Special Features, scattered moderate
convection is within 100 nm N of the ITCZ between 40W to 54W.

...GULF OF MEXICO...

A weak surface trough is located about 60 nm offshore of Texas
and SW Louisiana, paralleling the coastline. Showers and
thunderstorms are within 50 nm of the trough. Some isolated
thunderstorms are noted in the eastern Gulf and in the Bay of
Campeche. 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 continues to extend off the coast
from southwest Louisiana to south Texas. It will drift westward
toward the Texas coast this morning. 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
and exit the area during 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.

$$
AKR
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