[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 131800
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1805 UTC Wed Oct 13 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
1750 UTC.

...SPECIAL FEATURES...

Atlantic Gale Warning: A 1000 mb low pressure is just N of the
area near 31.5N 46.5W. An occluded front extends E from the low
to another low of 1002 mb near 31.5N42W. A cold front extends W
from the 1002 mb low to 29N49W to 31N55W. The morning ASCAT
passes show gale force SW to W winds extending southward to 29N
from the easternmost low. The ASCAT data also show near-gale
force W to NW winds extending southward to 28N from the
westernmost low. Scattered moderate isolated strong convection
with this system is noted north of 25N between 35W-47W. Expect
gale force SW to W winds north of 29N between 36W-47W through
this evening at 14/0000 UTC. As the low moves eastward, expect
the gales to move from west to east within this area. Seas of 11
to 13 ft are expected within the area of gale force winds.
Please read the latest High Seas Forecast issued by the National
Hurricane Center at website
https://www.nhc.noaa.gov/text/MIAHSFAT2.shtml for more details.

...TROPICAL WAVES...

An Atlantic tropical wave axis is along 30W from 03N-18N, moving
W at 10-15 kt. Moderate westerly upper-level winds over the
tropical wave, induced by an upper-level low near 24N23W, are
pushing much of the convection east of the wave axis. Scattered
moderate to isolated strong convection is observed from 09.5N to
13N between 23W-31W.

Another Atlantic tropical wave axis is along 51W/52W from
04N-17N, moving W at 10-15 kt. Scattered to numerous moderate
with embedded isolated strong convection is noted where the wave
interacts with the ITCZ from 07N to 10.5N between 48W-54W. The
northern portion of the wave is surrounded by dry Saharan air and
a subsident mid-level ridge axis, suppressing the development of
showers and thunderstorms.

An eastern Caribbean tropical wave axis extends from 19N66W
through Puerto Rico to Venezuela near 05N67W. The tropical wave
is moving W at 10-15 kt. Isolated to scattered showers are seen
between 60-120 nm E of the wave axis, mainly N of 15N.
Otherwise, mid to upper-level ridging is providing subsidence,
which is suppressing convection.

The western Caribbean tropical wave that had been analyzed along
80W at 13/0600 UTC has been repositioned slightly to the east
along 79W as of 1200 UTC, based on surface observations and
total precipitable water imagery. The tropical wave is moving W
at around 10 kt. No deep convection is noted in association with
the wave as it moves into a dry airmass, except for isolated
moderate showers along the wave south of 11N to Panama, near
where the wave intersects the east Pacific monsoon trough.

...MONSOON TROUGH/ITCZ...

A monsoon trough extends from the coast of Guinea-Bissau near
12N16W to 05N29W. The ITCZ is analyzed from 05N32W to 07N41W to
09N50W, then continues W of a tropical wave from 09N53W to
09N60W. Isolated moderate showers are along the monsoon trough
east of 25W. Scattered moderate and isolated strong convection
is noted along the ITCZ from 06.5N to 10.5N between 37W and 60W.

...GULF OF MEXICO...

A weak ridge extends from northern Georgia to the south-central
Gulf of Mexico and maintains tranquil weather conditions across
most of the basin. The pressure gradient between the ridge and
Tropical Storm Pamela over northern Mexico is resulting in fresh
to locally strong SE to S winds in the west-central Gulf of
Mexico, especially near the coast of southern Texas, where the
latest ASCAT pass shows 20-25 kt winds. SSE winds of 23 kt and
wave heights of 6 ft have recently been occurring at NOAA buoy
42020, located about 60 nm SE of Corpus Christi. Seas of 4 to 6
ft cover the western Gulf. Moderate E winds prevail east of 90W,
with 2 to 3 ft seas.

For the forecast, weak high pressure extending from the eastern
U.S. southwestward to the central Gulf and will influence the
Gulf waters during the next several days. Moderate to fresh
southerly winds are expected over the western Gulf between the
ridge and lower pressure over the Southern Plains and northern
Mexico through Thu. Gentle to moderate breezes will persist
elsewhere through Fri. A cold front will enter the NW Gulf Fri
night with fresh to strong northerly winds following it. The
front will reach from central Florida to the western Bay of
Campeche Sun morning with moderate to fresh N-NE winds across
most of the Gulf.

...CARIBBEAN SEA...

An upper-level low is centered near the NW Bahamas near 25N75W.
An upper-level trough extends SW from the upper-low to northern
Central America. Strong upper-level diffluence to the east of
the upper-trough is inducing numerous strong convection over the
central Caribbean from 12N to 15.5N between 71.5W and 74W.
Scattered moderate and isolated strong convection surrounds that
area, from 09N to 18.5N between 70.5W and 77W. The morning ASCAT
pass indicated a surface trough or possible outflow boundary
within the convection, extending along 74W from 12N to 18N.
Elsewhere, scattered showers and isolated tstorms over the NE
Caribbean are associated with a tropical wave, described in the
section above. The morning ASCAT pass shows gentle wind speeds
over the western Caribbean, west of 77W, where seas are likely 1
to 3 ft. Mainly moderate wind speeds are elsewhere east of 77W,
except for stronger winds likely within the strong thunderstorm
activity. Seas are 3 to 5 ft east of 77W, except higher in the
NE Caribbean passages, due to northerly swell from the Atlantic.
However, this northerly swell will subside tonight.

For the forecast, the vigorous upper-level trough extending from
the Bahamas to the NW Caribbean will support active weather
across the central Caribbean and extreme NE Caribbean through
tonight behind two tropical waves. Developing low pressure NE of
the southern Bahamas will drift E-NE tonight through the
weekend. This will weaken the pressure gradient across the
Caribbean basin, leading to tranquil marine conditions.

...ATLANTIC OCEAN...

An upper-level low is centered near the NW Bahamas. A weak
surface trough extends from 30N71W to 28N73W to 25N74W. A more
potent surface trough extends from 27N67W to 1010 mb low
pressure near 24.5N 70.5W to 21N71W. The morning ASCAT data
shows fresh to strong winds within 180 nm in the NE semicircle
of the low pressure center, while gentle to moderate wind speeds
prevail elsewhere across the western Atlantic, west of 60W.
Strong upper-level diffluence to the east of the upper-low is
inducing scattered moderate and isolated strong convection from
21N-30N between 64W-71W. Scattered moderate showers and isolated
tstorms are occurring within 60 nm either side of the
western/weaker surface trough, mainly north of 26.5N. Seas of 4
to 6 ft prevail over the western Atlantic, except up to 8 ft in
N swell to the NE of the Virgin Islands. The N swell across
these waters will subside tonight.

The 1010 mb low pressure near 24.5N 70.5W is forecast to drift
northward through tonight, then accelerate eastward on Thursday.
Development, if any, of this disturbance should be slow to occur
during the next couple of days due to unfavorable upper-level
winds, and there is a low chance of tropical cyclone formation
during the next 48 hours. Regardless of development, this system
will continue to produce very active weather and impact the
regional waters through late Thu. Locally heavy rainfall is
possible over portions of Hispaniola, the Turks and Caicos, and
the southeastern Bahamas during the next day or two.

Farther east, a surface ridge axis extends from 1020 mb high
pressure near 31N20W to 21N42W to a 1016 mb high pressure near
25N59W. Fair weather and light to gentle anticyclonic winds are
within 150 nm either side of the ridge axis. To the south, fresh
trades are noted from 09N to 16N between 30W and 60W, where seas
are mainly 7 to 8 ft. To the north of the ridge, strong to gale
force winds and thunderstorms are occurring, especially from
24N-31N between 36W-47W, described above in the Special Features
section.

The Cumbre Vieja volcano, on the island of La Palma in the
Canary Islands, has been erupting since 19 September 2021.
Significant volcanic ash is possible near the volcano. Marine
and aviation interests should monitor this ongoing situation by
reading the Volcanic Ash Advisory issued by Meteo-France at
http://vaac.meteo.fr/volcanoes/la-palma/

$$
Hagen
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