[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 112112
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0005 UTC Tue Oct 12 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
2100 UTC.

...TROPICAL WAVES...

A tropical wave was added to the analysis off the coast of West
Africa along 18W/19W. Scattered moderate convection is observed
from 03N to 08N between 17W and 22W.

A tropical wave is analyzed near 37W/38W, moving west at 10 kt. An
earlier scatterometer satellite pass showed a distinct surface
trough in this area. A few showers may be active from 05N to 09N
between 37W and 40W. This is a fairly shallow feature, and is in
a relatively unfavorable upper environment, with strong and dry NW
winds aloft. This is limiting convective growth to near the area
where the wave interacts with the ITCZ.

A tropical wave located along 57W/58W, moving west at 10 to 15
kt. 1010 mb low pressure is centered along the tropical wave near
13N57W or about 180 nm east of Barbados. Recent satellite-derived
wind data indicate that the system has not developed a well-
defined center. The potential for development of this system has
decreased, and strong upper-level winds should prohibit further
development on Tue. Regardless of development, the system could
produce locally heavy rainfall and gusty winds across portions of
the central and northern Lesser Antilles on Tue.

Another tropical wave is located over entering the central
Caribbean Sea along 70W/71W, moving west at 15 kt. A few showers
and thunderstorms are active from the northern Leeward Islands to
the eastern Dominican Republic, east of the wave axis. This is
where the wave is interacting with divergence aloft on the
southeast side of a broad upper low centered over the Cay Sal area
of the Bahamas.

A fifth tropical wave is near 86W extending southward through
Honduras and central Nicaragua, moving west at 15 to 20 kt. This
is in an area of deep layer subsidence with strong northerly winds
aloft and, no significant convection is noted near this tropical
wave.

...MONSOON TROUGH/ITCZ...

A monsoon trough extends from the mouth of the Gambia River near
13N16W to 07N25W to 07N30W. A segment of the ITCZ continues from
06N30W to 07N37W. Another ITCZ segment reaches from 07N40W to
07N50W. No significant convection is observed other than what is
described in the Tropical Wave section.

...GULF OF MEXICO...

A trough extends from southwest Florida along the Lower Florida
Keys to the southeast Gulf near 24N84W. Another trough extends
from near Clearwater, Florida to 23N86W. 1015 mb high pressure
centered near 27N88W dominates the remainder of the Gulf. No
significant shower or thunderstorm activity is evident. Moderate
to locally fresh SE winds are noted over the western Gulf, between
the high pressure and lower pressure over northeast Mexico. Seas
over the western Gulf are 4 to 6 ft. Light to gentle E to SE
breezes and slight seas are noted elsewhere.

For the forecast, the ridge will continue to dominate the Gulf
waters during the next several days. Moderate to fresh southerly
winds are expected into mid week over the western Gulf between
the ridge and lower pressure over the Southern Plains and northern
Mexico. Looking ahead, these winds may increase slightly Thu
before diminishing Fri ahead of a cold front expected to move into
the northwest Gulf Fri night. Strong northerly winds and building
seas are possible Sat. Gentle to moderate breezes will persist
elsewhere through Sat.

...CARIBBEAN SEA...

Regional land-based and buoy observations along with an earlier
scatterometer satellite pass confirm moderate to fresh winds
persist across the far eastern Caribbean, where the pressure
gradient is tight between two tropical waves and the Atlantic
ridge to the north of the region. Fresh to strong winds and
scattered squalls and tstms are possible in the northern Leewards.
Based on recent ship and buoy observations and an earlier
altimeter satellite pass, seas are 4 to 6 ft in the eastern
Caribbean. Gentle to moderate winds and slight to moderate seas
are evident elsewhere across the basin. In addition to the
convection extending from the northern Leeward Islands to
southeast Hispaniola, a few showers are evident from 13N to 15N
between 65W and 68W.

For the forecast, conditions will improve across the NE Caribbean
tonight as the wave moves W and gradually weakens. Another
tropical wave along 56W-57W is expected to approach the central
and northern Lesser Antilles early Tue, and move across the
Leeward Islands and Virgin Islands Tue afternoon through Tue
night. Expect similar active weather and strong gusty winds with
the wave passage. Northerly swell spreading across the central
Atlantic today will reach the regional Atlc waters and Caribbean
passages early Tue.

...ATLANTIC OCEAN...

A broad upper low centered over the Cay Sal area of the Bahamas
continues to support clusters of showers and thunderstorms over
much of the northern and central Bahamas, as well as over central
Cuba and southeast Florida. Additional showers and thunderstorms
are active northeast of the Turks and Caicos Islands from 23N to
25N between 68W and 71W. An associated surface trough reaches
along the coast of southeast Florida 29N80W to 1011 mb low
pressure near 26N80W to 23N86W in the southeast Gulf of Mexico.
Farther east, 1023 mb high pressure is centered near 34N53W. A
swath of moderate to fresh SE to S winds extends between the high
pressure and the trough from just north of the Leeward Islands to
just east of the Bahamas. Buoy observations hint seas may be as
high as 8 ft in this area of winds north of Puerto Rico, between
60W and 70W south of 23N.

Another upper low is centered near 23N60W with a trough extending
southward to near Barbados. Divergence aloft associated with this
trough is supporting the convection near the tropical wave along
56W/57W, but is also providing shear and deep layer dry air just
to the west of the tropical wave axis. A trough is analyzed from
32N31W to 26N47W. Light to moderate winds are noted north of 25N
between 35W and 65W, with moderate fresh trades farther south into
the tropics. Recent altimeter passes and buoy observations also
show evidence of northerly swell with wave heights from 8 to 11 ft
north of 25N between 35W and 65W. Seas are 4 to 6 ft elsewhere in
open waters east of 35W. East of 35W, scattered showers and
thunderstorms are evident just ahead of the cold front north of
27N between 30W and 35W. Light to gentle breezes are evident north
of 22N and east of 35W, with mostly moderate trades farther
south.

The Cumbre Vieja volcano, that is on the island of La Palma in
the Canary Islands, has been erupting since 19 September 2021.
Currently, significant volcanic ash is seen in the vicinity of
the volcano spreading eastward. 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 west of 65W, the trough off the east coast of
Florida will meander today, then drift eastward and weaken
through midweek. Northerly swell across the central Atlantic will
reach waters east of 72W late tonight through Tue. Low pressure
may form over the southeast Bahamas by Wed. Regardless of
development, locally heavy rainfall may persist over portions of
the Leeward Islands, Puerto Rico, and Hispaniola during the next
couple of days.

$$
Christensen
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