[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 150601
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0605 UTC Wed Sep 15 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 0000 UTC surface analysis and satellite imagery through
0500 UTC.

...SPECIAL FEATURES...

Tropical Depression Nicholas is centered near 30.0N 94.1W at
15/0300 UTC or 10 nm WNW of Port Arthur Texas moving ENE at 5
kt. Estimated minimum central pressure is 1004 mb. Maximum
sustained wind speed is 30 kt with gusts to 40 kt. Convection has
diminished in association with Nicholas. An area of fresh to
strong SW to W winds with seas to 8 ft is noted over the Gulf
waters N of 28N between 93W and 95W in association with the
circulation of Nicholas that is moving slowly across extreme
southeastern Texas. A slow motion toward the east is expected
through Wednesday night, followed by a northward drift on Thursday.
Continued gradual weakening is expected during the next couple of
days, and Nicholas is forecast to degenerate into a remnant low
tonight or early Thursday. Nicholas is expected to produce
additional rainfall amounts of 5 to 10 inches across portions of
southern and central Louisiana, southern Mississippi, far southern
Alabama, and the western Florida Panhandle through early Friday,
with isolated storm totals of 20 inches possible from southern
Louisiana to the far western Florida Panhandle. Life-threatening
flash flooding impacts, especially in urban areas, are possible
across these regions. Swells generated by Nicholas affecting
portions of the NW Gulf will continue to subside today. The last
public advisory has been issued by the National Hurricane Center
on this system. Future information on this system can be found in
Public Advisories issued by the Weather Prediction Center
beginning at 4 AM CDT, under AWIPS header TCPAT4, WMO header
WTNT34 KWNH, and on the web at http://www.wpc.ncep.noaa.gov.

A far eastern Atlantic tropical wave has an axis along 23W from
19N southward, moving west at 20 kt. A 1009 mb low pressure is
along the tropical wave axis near 10.7N23.1W, or a few hundred nm
south of the Cabo Verde islands. Showers and thunderstorms associated
with this low pressure continue to show signs of organization.
Environmental conditions are expected to remain conducive for
development, and a tropical depression is likely to form during
the next couple of days while the system moves generally westward
at about 15 mph across the eastern tropical Atlantic Ocean. This
system has a high chance of tropical cyclone formation within 48
hours. Please read the latest Tropical Weather Outlook at
www.hurricanes.gov for more details.

A surface trough extends from 29N69W to 22N73W reaching the SE
Bahamas. A 1013 mb low pressure is analyzed along the trough axis
near 25.5N70.5W. This system is producing a large area of
disorganized showers and thunderstorms, mainly from 23N-28N
between 65W-70W. Environmental conditions appear marginally
conducive for gradual development during the next few days, and a
tropical depression is likely to form while the system moves
north-northwestward to northward across the western Atlantic. This
system has a medium chance of tropical cyclone formation during
the next 48 hours, and a high chance through the next 5 days.
Regardless of development, increased winds and building seas are
expected north of 27N between 68W and 75W today and tonight.
Please read the latest Tropical Weather Outlook at
www.hurricanes.gov for more details.

...TROPICAL WAVES...

Refer to the Special Features section above for details on a
tropical wave and associated area of low pressure in the Atlantic
Ocean along 23W. In addition, a tropical wave is expected to
emerge off of the west coast of Africa toward the end of the week.
Environment conditions are forecast to be conducive for development
thereafter, while it moves generally west-northwestward over the
far eastern Atlantic.

A tropical wave is in the Atlantic Ocean along 42W from 04N to
17N, moving west at around 10 kt. Scattered moderate convection is
noted where the wave meets the monsoon from 05N to 10N between
40W and 46W.

A tropical wave is in the eastern Caribbean Sea along 67W/68W
crossing the Mona passage and moving west at around 15 kt. The
wave is helping to induce scattered moderate convection over the
Caribbean Sea just S of Puerto Rico and Dominican Republic. The
wave combined with an upper-level low spinning over Hispaniola
will support showers and thunderstorms over Puerto Rico and
Hispaniola today.

A tropical wave is in the western Caribbean Sea along 82W from
18N southward to across western Panama and into the eastern
Pacific Ocean, moving west at 15 to 20 kt. Isolated moderate
convection is near the wave axis from 10N to 13N.

...MONSOON TROUGH/ITCZ...

The monsoon trough emerges off the coast of Senegal near 14N17W
to 1009 mb low pressure near 10.7N23.1W to 13N32W to 08N47W. The
ITCZ continues from 08N47W to the NE coast of Venezuela near
08N60W. Aside from the convection mentioned above, scattered to
numerous moderate convection is noted SW of the low center from
04N to 07N between 25W and 30W.

GULF OF MEXICO...

Refer to the Special Features section above for details on
Tropical Depression Nicholas.

Middle and high cloudiness prevails over most of the Gulf region
and the State of Florida. Isolated showers and thunderstorm are
also noted over the Gulf waters. However, showers and thunderstorms
are more concentrated over the western Florida peninsula and the
Florida Keys under a diffluent pattern aloft. Gentle to moderate
SE-S return flow dominates the basin, with the exception of an
area of fresh to strong SW to W winds over the NW Gulf and just S
of Nicholas. Seas are in the 1 to 3 ft range east of 87W, and 3 to
6 ft range west of 87W, except 6 to 8 ft in the NW Gulf where the
strongest winds are.

For the forecast, fresh southerly winds will prevail over the north-
central Gulf today in association with the cyclonic circulation of
Nicholas. Then, a ridge will build westward across the Gulf waters
in the wake of Nicholas producing mainly gentle to moderate SE to
S winds the remainder of the week. Fresh easterly winds are expected
to the NW of the Yucatan peninsula beginning Fri night due to local
effects associated with a thermal trough.

CARIBBEAN SEA...

Refer to the Tropical Waves section above for details on the tropical
waves moving across the Caribbean Sea.

An upper-level low is centered over Hispaniola, enhancing scattered
showers and thunderstorms over the NE Caribbean, including Puerto
Rico and Hispaniola. Abundant mid to upper level clouds cover
Cuba, Jamaica and the NW Caribbean. This cloudiness is the result
of strong upper level northerly winds. Gentle to moderate trades
prevail across the basin, along with seas in the 2 to 4 ft range,
except 1 to 2 ft over the NW Caribbean Sea.

For the forecast, a weak pressure gradient will continue to provide
gentle to moderate easterly winds basin-wide. By tonight, moderate
to fresh winds will develop in the Gulf of Honduras and Gulf of
Venezuela and regional waters. Winds will further increase to fresh
to strong in the Gulf of Honduras and the south-central Caribbean
Thu night, continuing through Sat. Seas are forecast to build to
6-8 ft near the coast of Colombia by Thu night.

ATLANTIC OCEAN...

Refer to the Special Features section above for details on a
system in the far eastern tropical Atlantic Ocean that has a high
chance of tropical cyclone formation in the next 48 hours, and on
the system in the western tropical Atlantic, that has a medium
chance of tropical cyclone within the next 48 hours.

High pressure dominates the Atlantic forecast waters E of 60W with
a 1024 mb high center located near 34N38W. Another high pressure
center of 1023 mb is near the Azores. A surface trough remains W
of the Cabo Verde islands and extends from 21N29W to 13N33W.
mainly low clouds and limited shower activity is noted near the
trough axis. Moderate to fresh winds NE-E winds are noted near
the northern end of the trough. An area of fresh to strong northerly
winds is E of 20W to the coast of Mauritania due to the pressure
gradient between the ridge and lower pressures over W Africa.
Gentle to moderate winds dominate the entire rest of basin under
the influence of a ridge.

For the forecast west of 65W, a weak surface ridge will provide
mainly gentle to moderate easterly winds, locally fresh over the
offshore waters east of the Bahamas due to convection associated
with a trough that reaches the SE Bahamas.

$$
GR
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