[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 151753
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1753 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 1200 UTC surface analysis and satellite imagery through
1745 UTC.

..SPECIAL FEATURES...

Tropical Depression Nicholas is centered near 30.4N 92.8W at
15/1500 UTC or 25 nm NE of Lake Charles LA moving ENE at 4 kt.
Estimated minimum central pressure is 1006 mb. Maximum sustained
wind speed is 25 kt with gusts to 30 kt. The center of Nicholas
is largely devoid of deep convection, with most of the activity
located over the Mississippi Valley and extending to the NW Gulf
of Mexico. The forward speed is expected to slow through the
next 24 hours before a gradual turn to the north prior to
dissipation. Continued weakening is forecast during the next 48
hours with the center of circulation possibly becoming quite
diffuse by late Thursday. However, heavier rainfall will
continue to remain a threat as tropical moisture persists across
the Gulf Coast region. Nicholas is expected to produce
additional rainfall amounts of 3 to 6 inches across the central
Gulf coast in central to southeastern Louisiana, southern
Mississippi, southern Alabama and the Florida Panhandle through
Friday, with isolated storm totals of 10 inches possible. Life-
threatening flash flooding impacts, especially in urban areas,
remain a possibility in these areas. Swells generated by
Nicholas affecting portions of the NW Gulf will continue to
subside today. The Weather Prediction Center is using the
advisories on TD Nicholas and they can be found under AWIPS
header TCPAT4, WMO header WTNT34 KWNH, and on the web at
http://www.wpc.ncep.noaa.gov.

A surface trough extends from 30N71W to 23N75W reaching the
central Bahamas. A 1011 mb low pressure is analyzed along the
trough axis near 28N73W and satellite imagery indicate that it is
becoming better defined. This system is producing a large area of
disorganized showers and thunderstorms, mainly over the eastern
semicircle, from 20N and 30N, and between 64W to 74W. Recent
scatterometer satellite data show fresh to strong SE-S winds in
the area of convection. Environmental conditions are expected to
become more conducive for development, and a tropical depression
is likely to form during the next day or two while the system
moves north- northwestward to northward off the southeast U.S.
coast. The Air Force Hurricane Hunters are currently enroute to
investigate the disturbance. This system has a high chance of
development in the next 48 hours. 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.

An Atlantic tropical wave has its axis along 26W, south of 17N,
and it is moving W at 20 kt. A 1009 mb low pressure is along the
tropical wave axis near 10N26W, or a few hundred nm SSE of the
Cabo Verde islands. Scattered moderate to isolated strong
convection is noted on the northern semicircle, especially from
10N to 15N and between 24W and 31W. Environmental conditions are
expected to remain conducive for development, and a tropical
depression is likely to form within the next couple of days. This
system is expected to move westward to west-northwestward across
the tropical Atlantic during the next several days. 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.

...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.

An Atlantic tropical wave has its axis along 44W, south of 17N,
and moving W at around 10 kt. Scattered moderate convection is
noted where the wave meets the monsoon trough from 07N to 12N and
between 39W and 48W.

A Caribbean Sea tropical storm has its axis along 71W, south of
20N, extending from Hispaniola to W Venezuela, and moving W at
around 15 kt. The wave is helping to induce scattered moderate
convection over the eastern Caribbean Sea, affecting the waters of
the Mona Passage, Puerto Rico and US Virgin Islands. This wave,
combined with an upper- level low spinning over Hispaniola, will
support showers and thunderstorms over Puerto Rico and Hispaniola
today.

Another Caribbean Sea tropical wave has its axis along 84W, south
of 18N, extending across E Honduras, Nicaragua and Costa Rica into
the eastern Pacific Ocean, and it is moving W at around 15 kt.
Isolated moderate convection is noted near the northern wave
axis in the W Caribbean Sea.


...MONSOON TROUGH/ITCZ...

The monsoon trough emerges off the coast of Senegal near 15N16W to
the 1009 mb low pressure near 10N26W to 12N35W to 08N48W. The
ITCZ continues from 08N48W to the coast of Guayana near 07N58W.
Aside from the convection mentioned above, scattered moderate
convection is noted well SW of the low center from 07N and
between 28W and 36W.

GULF OF MEXICO...

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

Tropical Depression Nicholas is centered over SW Louisiana and its
tail is causing a line of showers and thunderstorms that extends
from SE Louisiana to NE Mexico, with the strongest storms in the
area from 23N to 27N and between 92W and 96W. Scattered moderate
convection is also noted in the NE Gulf, mainly within 100 nm of
the coasts of Alabama and NW Florida. Fairly tranquil weather
conditions are present in the rest of the basin.

Fresh to locally strong SW-S winds are found in the N Gulf of
Mexico, mainly N of 26N and W of 88W, associated with the
influence of Nicholas. Seas in the area are 3-6 ft. The rest of
the Gulf is experiencing moderate to fresh anticyclonic winds with
seas of 1-3 ft.

For the forecast, conditions related to the impact of Tropical
Depression Nicholas will continue to gradually improve for
offshore Louisiana and upper Texas coasts. For the remainder of
the week, gentle to moderate mainly southerly flow will dominate
the basin. .

CARIBBEAN SEA...

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

Moisture in the SW Caribbean Sea associated with the E Pacific
monsoon trough results in scattered moderate showers within 60 nm
of the coasts of Costa Rica, Panama and NW Colombia. The rest of
the basin experiences fairly tranquil weather conditions. The low
pressure to the north of the Caribbean is causing a weak pressure
gradient across the region, resulting in moderate to fresh trades,
with the strongest winds located in the Gulf of Honduras. Seas
are 2-4 in the SE Caribbean and Gulf of Honduras, while 1-2 ft
seas are found elsewhere.

For the forecast, winds will increase to moderate to fresh in the
central and eastern Caribbean starting tonight, with locally
strong winds possible into the weekend offshore Colombia and in
the Gulf of Honduras.

ATLANTIC OCEAN...

Refer to the Special Features section above for details on the
disturbance NE of the Bahamas and the system in the far eastern
Atlantic.

The 1026 mb subtropical ridge is centered near the Azores and
dominates most of the tropical Atlantic. A surface trough is
located in the central Atlantic from 30N43W to 25N44W and there
are a few showers near the trough axis. Another surface trough is
located from 14N33W to 22N34W and it is devoid of any significant
convection. The rest of the basin is fairly quiet. Fresh to strong
N-NE winds are present off the coast of Mauritania, mainly E of
20W, due to the pressure gradient caused by the ridge and lower
pressures over W Africa. This area also experiences seas of 6-9
ft. Gentle to moderate winds and seas of 3-6 ft can be found in
the rest of the basin.

For the forecast west of 65W, weak high pressure will lead to
gentle to moderate mainly easterly winds across the basin.

$$
DELGADO
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