[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 091801
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1805 UTC Sat Oct 9 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
1755 UTC.

...SPECIAL FEATURES...

An area of low pressure located about 150 miles SE of Wilmington,
North Carolina, continues to produce a large area showers and
thunderstorms. Scattered moderate convection extends southward to
the NW Bahamas and between 72W and 78W. Satellite-derived wind
data and surface observations indicate the disturbance is
producing a broad area of gale-force winds to the west and north
of the center. Associated shower and thunderstorm activity has
been gradually increasing and becoming better organized today, and
the low could acquire subtropical characteristics late this
afternoon through early Sunday. However, by late Sunday and
Monday, environmental conditions should become unfavorable for any
further development. The low is forecast to move slowly
northwestward during the next day or so, and approach the North
Carolina coast tonight and early Sunday. Therefore, interests
along the North Carolina coast should monitor the progress of this
system.

Regardless of development, intermittent periods of locally heavy
rains and gusty winds will affect southeastern and eastern portions
of North Carolina during the next day or two. An Air Force
Reserve reconnaissance aircraft is currently investigating the
gale area. There is a medium chance of development for this low
over the next 48 hours. For more details, please read the latest
Tropical Weather Outlook at https://www.hurricanes.gov and
Mariners can read the latest High Seas Forecast from the Ocean
Prediction Center at https://ocean.weather.gov for more
information.

...TROPICAL WAVES...

An Atlantic tropical wave has its axis along 45W, south of 18N,
and it is moving W at 15 to 20 kt. Recent scatterometer satellite
data and satellite imagery depict a well-defined surface trough
and wind shift. Fresh to locally strong trades are noted from 09N
to 19N and between 37W to 47W. Scattered moderate to isolated
strong convection is observed from 05N to 13N and between 33W and
52W.

A second Atlantic tropical wave has its axis along 59W, south of
20N, and it is moving W near 15 kt. Recent scatterometer satellite
data and satellite imagery show a broad surface curvature and
fresh to locally strong trades from 11N to 19N and between 52W and
the Lesser Antilles. The wave is interacting with an upper level
trough resulting in a large area of showers and isolated
thunderstorms, mainly from 11N to 18N and between 53W and 64W,
including the Windward Islands. The stormy weather conditions will
expand to the rest of the Lesser Antilles later today, affecting the
Virgin Islands and Puerto Rico on Sunday and Hispaniola on
Monday.

A Caribbean tropical wave has its axis along 73W, south of 20N,
extending from Haiti to E Colombia, and it is moving W near 15 kt.
No deep convection is noted in association with this wave.

...MONSOON TROUGH/ITCZ...

The monsoon trough enters the Atlantic Ocean through the coast of
Mauritania near 17N16W and continues SW to near 08N24W. The ITCZ
extends from 08N24W to 08N35W and to 07N45W. Another segment of
the ITCZ extends from 07N47W to 11N58W. Scattered moderate to
isolated strong convection is found within 150 nm on either side of
the ITCZ and monsoon trough between 27W and the coast of Africa.

...GULF OF MEXICO...

A weak 1018 mb high pressure over the Mississippi Valley dominates most
of the Gulf of Mexico behind a deep upper level trough that has
cleared most of the basin. Dry continental air behind the upper
level trough maintains tranquil weather conditions. A couple of
surface troughs extending from low pressures off the SE United
States are crossing Florida and poking the E Gulf, but no
convection are associated with these features. However, atmospheric
conditions are favorable for afternoon and evening thunderstorms
to develop across South Florida, likely also affecting the
surrounding waters. Another surface trough is located in the Bay
of Campeche, along 93W and south of 21N. A few showers are
observed near the trough axis, but the convection is quickly
weakening. The weak pressure gradient allows moderate or weaker
easterly winds to prevail. Seas are 1-3 ft in the Gulf.

For the forecast, a weak surface ridge will start to build across
the basin this evening and moderate to locally fresh return flow
will develop over the western half of the basin, continuing
through Wed night.

...CARIBBEAN SEA...

A tropical wave approaching the Lesser Antilles, previously
described in the Tropical Waves section, is producing showers and
isolated thunderstorms in the E Caribbean. The E Pacific monsoon
trough enters the SW Caribbean through the coast of Costa Rica and
extends to the coast of NW Colombia. Scattered moderate convection
is noted near the trough axis and within 60 nm of the countries in
the region. A weak surface trough in the NW Caribbean extends from
17N to 22N along 84W and is generating a few shallow showers near
the trough axis. Recent satellite-based wind data indicate fresh
to locally strong trades occurring from 12N to 18N and between 65W
and the Lesser Antilles. Fresh trades are also noted within 130 nm
of the NW coast of Colombia. Moderate or weaker winds are present
elsewhere in the Caribbean. Seas of 3-6 ft are prevalent in the E,
central and SW Caribbean, while 1-3 ft prevail elsewhere.

For the forecast, the aforementioned tropical wave located E of
the Lesser Antilles will provide fresh winds and scattered
showers to the Lesser Antilles today through Monday. Shower
activity associated with this wave will affect the US/UK Virgin
Islands and Puerto Rico Sun evening through the middle of next
week and Hispaniola from Mon through Wed night. Seas to 8 ft
associated with this wave will affect the Atlantic waters E of the
Lesser Antilles through Sun evening. Otherwise, moderate to fresh
winds in the eastern half of the Caribbean will diminish to
gentle to moderate early on Tue and to light to gentle on Thu.

...ATLANTIC OCEAN...

A surface trough extends from 26N59W to 22N71W and it is producing
a few showers and isolated thunderstorms near the trough axis.
Another surface trough is located from 30N42W to 25N54W and
scattered moderate convection is observed near the E extent of the
trough axis and north of the tropical Atlantic. The rest of the
basin is dominated by a fairly dry weather regime, suppressing the
development of showers and thunderstorms.

Satellite-derived wind data indicate that fresh to strong
southerly winds are found N of 26N and between 36W and 46W. The
pressure gradient between the 1031 mb Azores high pressure and
lower pressures over NW Africa results in fresh to locally strong
NE winds from 18N to 27N and E of 27W. Moderate or weaker winds
are found elsewhere in the basin. Seas of 3-6 ft are present W of
60W, while seas of 6-9 ft are found in the rest of the tropical
Atlantic, with the highest seas occurring E of the Lesser Antilles
and N of the Cabo Verde Islands.

The Cumbre Vieja volcano, that is on the island of La Palma in
the Canary Islands, has been erupting since 19 September 2021.
Currently, volcanic ash is not easily detectable due to cloud
cover. Marine and aviation interests should monitor this on-
going situation, by reading the Volcanic Ash Advisory, that is
issued by Meteo-France, at http://vaac.meteo.fr/volcanoes/la-
palma/.

For the forecast, a well-defined, non-tropical low pressure
system located about 175 nmi SE of Morehead City and Wilmington,
North Carolina, continues to produce a large area of cloudiness
and disorganized showers and thunderstorms over the offshore
waters N of the Bahamas. Environmental conditions could briefly
become marginally conducive for the low to acquire subtropical
characteristics through early Sunday. The low is forecast to move
slowly NW during the next day or so, and approach the North
Carolina coast tonight and early Sunday. Regardless of
development, a trough extending from the low will continue to
generate showers over the SW N Atlc waters through Mon.

$$
DELGADO
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