[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 151025
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1205 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 0600 UTC surface analysis and satellite imagery through
1120 UTC.

..SPECIAL FEATURES...

Tropical Depression Nicholas is centered near 30.1N 93.8W at
15/0900 UTC or NNE of Port Arthur Texas moving ENE at 5 kt.
Estimated minimum central pressure is 1004 mb. Maximum sustained
wind speed is 25 kt with gusts to 30 kt. Convection has
diminished in association with Nicholas. 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 day, 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 29N70W to 23N75W reaching the S
Central Bahamas. A 1012 mb low pressure is analyzed along the
trough axis near 26N71W. This system is producing a large area of
disorganized showers and thunderstorms, mainly from 20N-30N
between 69W-75W. 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 24W. 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 trough from 04N to 11N
between 40W and 48W.

A tropical wave is in the eastern Caribbean Sea along 68W
crossing the Mona passage and moving west at around 15 kt. The
wave is helping to induce scattered moderate convection over the
eastern Caribbean Sea between the Mona Passage, S of Puerto Rico
and The U.S. Virgin Islands. 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 near the border of Panama and Costa Rica into the
eastern Pacific Ocean, moving west at 15 to 20 kt. Isolated
moderate convection is near the wave axis from 12N to 15N.

...MONSOON TROUGH/ITCZ...

The monsoon trough emerges off the coast of Senegal near 12N16W
to 1009 mb low pressure near 10N24W to 11N34W to 07N47W. The
ITCZ continues from 07N47W to 08N58W. Aside from the convection
mentioned above, scattered to numerous moderate convection is
noted SW of the low center from 01N to 07N between 26W and 31W.

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 west of 90W from 23N to 29N. Gentle to
moderate SE-S return flow dominates the basin, except for an area
of fresh to strong SW to W winds over the NW Gulf and just S of
Nicholas. Seas are in the 2 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 1020 mb high center located near 31N55W. Another high
pressure center of 1022 mb is near the Azores. A surface trough
remains W of the Cabo Verde islands and extends from 21N32W to
14N33W. 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.


$$
Torres
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