[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 121015
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1205 UTC Sun Sep 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 0600 UTC surface analysis and satellite imagery through
1020 UTC.

...SPECIAL FEATURES...

Showers and thunderstorms over the Bay of Campeche and southern
Gulf of Mexico have been increasing during the past several hours
near and east of a surface trough of low pressure.  A tropical
depression is expected to form later today or tonight while the
system moves northwestward and then northward near the coast of
northeastern Mexico.  Additional development is possible through
the middle of next week if the system remains over water, and
interests along the western and northwestern Gulf coast should
monitor the progress of this disturbance.  An Air Force Hurricane
Hunter aircraft is scheduled to investigate the system this
morning, and potential tropical cyclone advisories could be
initiated later today. Regardless of development, the disturbance
will continue to produce heavy rain across portions of southern
Mexico today, including the western Yucatan Peninsula, which may
lead to flash flooding and mudslides. By late today, heavy rain is
expected to reach portions of the Texas and Louisiana coasts with
a heavy rain threat continuing across those coasts through the
middle of the week. Localized significant rainfall amounts are
possible, potentially resulting in areas of flash, urban, and
isolated river flooding. The chance of tropical cyclone formation
within the next 48 hours is high.

...TROPICAL WAVES...

An Atlantic tropical wave has an axis along 25W south of 21N,
moving W at 15-20 kt. A 1010 mb low is analzyed along the wave
near 17N25W. Scattered moderate to isolated strong convection is
noted north of the low from 17N to 20N between 23W and 26W. The
National Hurricane Center is tracking this disturbance for
possible tropical development over the next few days. Currently,
it has a low chance of development over the next 48 hours.

An Atlantic tropical wave has an axis along 47W south of 22N,
moving W at 15 kt. The wave is surrounded by dry Saharan air,
which is inhibiting convection at this time.

A Caribbean tropical wave has an axis along 68W south of 21N,
moving W at 15-20 kt. This wave is moving in tandem with an upper
level trough and is producing scattered moderate to isolated
strong convection from 17N to 22N between 65W and 71W, impacting
Hispaniola, Puerto Rico, and the Virgin Islands.

A Caribbean tropical wave has an axis along 83W south of 15N,
moving W at 10 kt. A few showers are noted near the wave axis,
mainly north of Panama, but no significant convection is
associated with this feature.

...MONSOON TROUGH/ITCZ...

The monsoon trough passes through the coast of Mauritania near
19N16W to the 1010 mb low pressure near 16N 23W to 13N30W and to
06N40W. The ITCZ continues from 06N41W to 06N45W. No significant
convection is observed near the monsoon trough or ITCZ, other than
the storms affecting the Cabo Verde Islands.

GULF OF MEXICO...

See the Special Features section above for details on the
disturbance over the eastern Bay of Campeche and a description of
the upper-level trough in the area. In addition to those
features, a surface trough extends from the Bay of Campeche near
19N94W to the W Gulf of Mexico near 26N96W. Also, a weakening
stationary front is located over the NE Gulf of Mexico. Numerous
moderate to scattered strong convection is noted in the E Bay of
Campeche, central and SE Gulf due to the interaction between the
surface features described and an upper level trough in the
vicinity. A few showers are noted in the NE Gulf, while fairly
tranquil weather conditions prevail in the NW Gulf.

Recent scatterometer satellite data and surface observations show
fresh to strong cyclonic winds W of 86W, with the strongest winds
noted in the north-central Gulf and within 100 nm the coast of
Veracruz, Mexico. Moderate to locally fresh easterlies are
observed in the SE and NW Gulf, while gentle to moderate winds are
present in the NE Gulf. Seas of 4-7 ft prevail in the N Gulf,
while 3-6 ft are present elsewhere in the basin, with the
exception of 2-4 ft in the NE Gulf.

For the forecast, please see the Special Features section above
for more information about the potential for tropical cyclone
development in the western Gulf. Elsewhere, quiescent conditions
are expected to prevail across the central and eastern Gulf
through midweek.

CARIBBEAN SEA...

Please see the Tropical Waves section above for details on the
tropical waves along 66W and 82W.

Aside from the scattered moderate convection being generated by
the passing tropical waves, isolated evening thunderstorms are
noted affecting SW Haiti and nearby waters. The rest of the
Caribbean Sea enjoys fairly tranquil weather conditions. Fresh to
isolated strong trades are observed in the most recent
scatterometer satellite data across the central Caribbean and Gulf
of Honduras, with the strongest winds seen in the Gulf of
Venezuela. Moderate to fresh trades are noted in the NE Caribbean,
while gentle to moderate trades prevail in the NW and SW
Caribbean. Seas of 5-8 ft are present in the central Caribbean
and Gulf of Honduras and 2-5 ft are prevalent elsewhere.

For the forecast, the Atlantic ridge will continue to build westward
across the Caribbean, bringing an increase in the trade wind
flow through weekend. Fresh to strong winds will occur offshore
Colombia and in the Gulf of Venezuela, mainly at night through
Sun. Fresh to strong winds are also likely in the late evening
in the Gulf of Honduras through late Sun. By Mon, gentle to
moderate trade winds will prevail through midweek.

ATLANTIC OCEAN...

A 1028 mb subtropical ridge positioned over the central Atlantic
dominates most of the tropical portion of the basin. A stationary
front is stretches from 31N66W to Cape Canaveral, Florida, and a
few showers are noted along the boundary. Low-level convergence is
allowing for a few showers and isolated thunderstorms near the NW
Bahamas and off SE Florida. A cold front stretches from an
occluding low located between the Azores and Portugal, to 31N24W
to 30N38W. Most of the convective activity along this front is
noted north of our area, with only a few showers seen along the
boundary betwen 24W and 38W. A trough is analyzed from 16N53W to
11N55W and scattered moderate convection is noted from 13N to 17N
and between 52W and 57W. The rest of the basin enjoys fairly
tranquil weather conditions.

Recent scatterometer wind data show fresh to strong E-NE winds
north of Hispaniola to 22N and on the northern part of the trough
east of the Lesser Antilles, mainly from 14N to 22W and between
52W to 60W. An area of moderate to fresh easterlies is observed in
the satellite wind data from 18N to 25N and between 25W to 40W.
Seas in this region are 4-7 ft. Seas of 4-7 ft are also found east
of the Leeward Islands to 50W, from 14N to 22N. Gentle to
moderate winds and seas of 3-6 ft prevail in the rest of the
tropical Atlantic.

For the forecast west of 60W, A frontal boundary will linger across the area
through Mon bringing showers and thunderstorms across the area.
Otherwise, quiescent conditions will prevail through Thu.

$$
AKR
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