[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 281810
TWDAT

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

...SPECIAL FEATURES...

Sam, a Category 4 Hurricane was centered near 17.5N 54.3W at
28/1500 UTC or 505 nm E of the Northern Leeward Islands, and
moving NW at 7 kt. Estimated minimum central pressure is 952 mb.
Maximum sustained winds are 115 kt with gusts to 140 kt. Seas are
peaking at 36 to 39 ft near the center, and from 28 to 35 ft up to
70 nm farther out. Latest satellite imagery shows a cloud-filled
eye. Numerous moderate to scattered strong convection is up to 75
nm in a NE semicircle, and up to 55 nm in a SW semicircle.
Scattered moderate convection is present up to 60 nm farther out
NW, N and NE of the center. A NW motion will continue through Thu
morning with a gradual increase in speed by Wed, then follow by a
turn toward the N by Friday. On the forecast track, Sam will pass
well NE of the Northern Leeward Islands Wed and then Puerto Rico
Thu. 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/

Showers and thunderstorms are showing signs of organization in
association with a tropical wave and broad area of low pressure
located about 530 nm SSE of the Cabo Verde Islands. Environmental
conditions are conducive for development, and a tropical
depression is likely to form in a day or two while the disturbance
moves west- northwestward at 10 to 15 mph over the eastern
tropical Atlantic. There is a high chance for formation in the
next 48 hours.

A broad area of low pressure located about 600 nm SW of the Cabo
Verde Islands continues to produce an area of disorganized showers
and thunderstorms. Environmental conditions are conducive for
gradual development, and a tropical depression is likely to form
during the next couple of days while the system moves westward to
west-northwestward at 5 to 10 mph over the central tropical
Atlantic. There is a high chance for formation in the
next 48 hours.

A well-defined low pressure area associated with the remnants of
Peter is located about 350 miles ENE of Bermuda. The associated
showers and thunderstorms have increased a little this morning,
but are still not well organized. This system could become a
short-lived tropical depression while moving northeastward at
about 10 mph before upper-level winds increase on Wednesday. There
is a medium chance for formation in the next 48 hours. In
addition, the Ocean Prediction Center (OPC) has issued a Gale
Warning for this system, please visit oceanweather.com for more
information.

Please refer to the latest NHC Tropical Weather Outlook at
www.hurricanes.gov for more details on all three tropical
disturbances.

...TROPICAL WAVES...

An Atlantic tropical wave is SSE of the Cabo Verde Islands near
20W from 16N southward through the aforementioned low pressure
near 07N20W, and moving W at 10 to 15 kt. Numerous moderate to
strong convection is flaring up from 03N to 10N between 15W and
22W. Refer to the Special Features section above for the
formation potential of this wave.

Another Atlantic tropical wave is along 37W from 16N southward
and moving W near 15 kt. Scattered moderate convection is seen
from 04N from 11N between 34W and 38W.

The weak Atlantic tropical wave previously located near 43W has
been absorbed by the strong ridge to the SE of Hurricane Sam.

A Caribbean tropical wave is along 79W from W Jamaica southward to
E Panama, and moving W near 10 kt. Enhanced by the E Pacific
monsoon trough, numerous heavy showers and scattered thunderstorms
are occurring across Panama and NW Colombia, including adjacent
waters.

...MONSOON TROUGH/ITCZ...

A monsoon trough enters the Atlantic near the Guinea Bissau-Guinea
border near 11N15W through the aforementioned 1010 mb low
pressures 07N20W and 09N33W to 06N39W. Numerous moderate to
strong convection is present from 03N to 09N between 22W and 26W.
Scattered moderate convection is found farther W from 03N to 12N
between 26W and 34W. Latest satellite scatterometer and altimetry
data reveal moderate to fresh with locally strong monsoon winds
and seas of 7 to 9 ft near and S of the monsoon trough, from 01N
to 07N between 18W and 30W.

...GULF OF MEXICO...

A weak but persistent surface trough over S Texas and Louisiana is
triggering scattered showers and thunderstorms across the N
central Gulf. Locally moderate winds and seas up to 4 ft are
possible near these showers and thunderstorms. Otherwise, a broad
ridge of high pressure extending southwestward from N Florida to
central Mexico continues to promote light to gentle winds and seas
of 2 to 3 ft for much of the Gulf.

For the forecast, the ridge will maintain light to gentle winds
and slight seas across the Gulf through mid week. Moderate to
fresh winds will follow a weak cold front that will move into the
E Gulf toward the end of the week and then exit the area during
the weekend. Moderate to locally fresh winds are also expected
across the SE Gulf later in the week due to a persistent trough
in that region.

...CARIBBEAN SEA...

Modest convergent trade winds are causing isolated thunderstorms
near the Cayman Islands and the SE basin. Refer to the Tropical
Waves section for additional convection in the basin. Moderate to
locally fresh trades and seas at 4 to 5 ft are evident over the S
central basin. Light to gentle trades and seas of 2 to 3 ft
prevail for the rest of the Caribbean Basin.

For the forecast, major Hurricane Sam will pass well NE of the
Northern Leeward Islands Wed, then turn northward to SE of
Bermuda through early Sat. Meanwhile, moderate trades will continue
over much of the Caribbean today. Gentle trades will then prevail
over the Caribbean through Fri. Swells generated by Sam are
forecast to persist near 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 tropical disturbances in the Atlantic
Basin.

The Cumbre Vieja volcano on the island of La Palma in the Canary
Islands has been erupting since 19/1410 UTC. Based on footage
from nearby webcams, the volcanic ash plume is reaching near
20,000 ft or 6,000 meters; and is drifting eastward. 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 28/2100 UTC.

A stationary front meanders southwestward from near Bermuda across
31N65W to the central Bahamas. A surface trough is also in the
vicinity, curving northeastward from S of this front at 26N70W to
beyond 31N58W. These features are producing scattered showers and
isolated thunderstorms N of 24N between 57W and the central
Bahamas.

In the E central Atlantic, a surface trough near 28N33W is
generating scattered moderate convection W of the Canary Islands, N
of 26N between 27W and 37W. Refer to the Tropical Waves and
Monsoon Trough/ITCZ sections for additional convection across the
Atlantic Basin. N of 22N, light to gentle winds and seas at 3 to
4 ft are found between 62W and the Georgia-Florida coast; gentle
winds with locally moderate winds and seas of 5 to 7 ft are seen
between 30W and 62W. Farther E, moderate to fresh with locally
strong NE trades and seas at 8 to 11 ft are present near the
Canary Islands, N of 20N between the NW African coast and 30W.
Outside the influence of Hurricane Sam, gentle to moderate trades
and seas of 5 to 7 ft exit from 10N to 22N/20N between the African
coast and the Lesser Antilles. Besides stronger monsoon winds and
higher seas mentioned in the Monsoon Trough/ITCZ section, mainly
gentle monsoon winds and seas at 4 to 7 ft prevail across the
remainder of the basin.

For the forecast W of 50W, light to gentle breezes are expected
to prevail with slight seas through Thu W of 65W. Meanwhile,
Hurricane Sam was near 17.5N 54.3W 952 mb at 28/1500 UTC and
moving NW at 7 kt. Maximum sustained winds are 115 kt with gusts
to 140 kt. Sam will move to 18.2N 55.1W this evening, 19.2N 56.5W
Wed morning, 20.5N 58.1W Wed evening, 22.0N 59.6W Thu morning,
24.0N 60.9W Thu evening, and 26.6N 61.5W Fri morning. Sam will
change little in intensity as it moves north of the area by early
Sat, staying east of Bermuda. 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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