[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 160602
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0605 UTC Thu Sep 16 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 30.1N 91.9W at
16/0300 UTC or 10 nm SE of Lafayette Louisiana stationary.
Estimated minimum central pressure is 1006 mb. Maximum sustained
wind speed is 25 kt with gusts to 35 kt. A trailing trough is
analyzed over the Gulf of Mexico and extends from 30N92W to
24N94W. The depression is currently nearly stationary over
southern Louisiana, but is expected to gradually move northward
over the next couple of days. The center of Nicholas may become
ill-defined over the next couple of days as it evolves into a
post-tropical remnant low with minimal thunderstorm activity near
its center. Nicholas is expected to produce additional rainfall
amounts of 2 to 5 inches across the central Gulf coast in
southeastern Louisiana, southern Mississippi, southern Alabama and
the Florida Panhandle through Friday, with isolated storm totals of
8 inches possible. Considerable flash flooding impacts, especially
in urban areas, are possible across these regions. Widespread minor
river flooding is expected, while scattered moderate river flooding
is possible, across portions of southeastern Louisiana, southern
Mississippi, southern Alabama, and the Florida Panhandle. The
Weather Prediction Center is issuing advisories on Nicholas and
they can be found at http://www.wpc.ncep.noaa.gov.

A surface trough extends from 31N73W to broad 1010 mb low pressure
located near 29.3N74W to just N of Andros Island in the Bahamas.
Most of the convective activity associated with this low is displaced
to the E of the center and covers the area from 27N to 31N between
70W and 72W. Fresh to strong winds associated with this system
are also noted to the E of the low center and mainly from 28N to
31N between 68W and 74W. An Air Force Reserve Hurricane Hunter
aircraft investigating the system Wed afternoon reported that the
circulation was disorganized and that the strongest winds were
well to the east of the center. Environmental conditions are
expected to become more conducive for development, and a tropical
depression is still likely to form during the next day or two
while the system moves north-northwestward to northward off the
southeast U.S. coast. Regardless of development, this system could
bring high surf to portions of the southeast and mid- Atlantic
U.S. coasts later this week. This system has a high chance of
tropical cyclone formation in the next 48 hours. Please read the
latest Tropical Weather Outlook at www.hurricanes.gov for more
details.

A tropical wave is in the Atlantic Ocean along 31W/32W from 03N
to 17N, with 1011 mb low pressure along the wave near 11.5N31.5W,
or more than 500 miles west-southwest of the Cabo Verde Islands,
moving west at 15 to 20 kt. Showers and thunderstorms have changed
little in organization in association with this area of low pressure.
In addition, earlier satellite derived winds indicated the system
also lacks a well-defined center. However, environmental conditions
are still expected to remain conducive for development, and a
tropical depression is likely to form during 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 in the next
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 31W/32W.

Another tropical wave is expected to emerge off of the west coast
of Africa in a day or two. Thereafter, environmental conditions
are forecast to be conducive for development while the system
moves generally west-northwestward to northwestward over the far
eastern Atlantic. Currently, a large cluster of moderate to
isolated strong convection is affecting most of Senegal, The
Gambia and the SW of Mauritania.

A tropical wave is in the Atlantic Ocean along 46W, from 04N to
17N, moving west at around 10 kt. Convection is limited near the
wave axis.

A tropical wave is in the Caribbean Sea along 74W from 20N
southward across Haiti to the Colombia-Venezuela border, moving
west at 10 to 15 kt. The tropical wave combined with a mid to
upper level low and daytime heating are helping to induce
scattered showers and thunderstorms across the Greater Antilles
and adjacent waters.

A tropical wave is over Central America along 87W from 18N
southward across Honduras and western Nicaragua and into the
eastern tropical Pacific Ocean, moving west at 10 to 15 kt. The
tropical wave is helping to support scattered showers and
thunderstorms over portions of northern Central America.

...MONSOON TROUGH/ITCZ...

The monsoon trough emerges off the coast of Africa through Senegal
near 15N17W to 1011 mb low pressure located near 11.5N31.5W to
11N40W to 07N52W. The ITCZ continues from 07N52W to the coast of
Guyana near 08N59W. Aside from the convection mentioned above,
scattered moderate convection is noted from 11N to 13N between
38W and 41W.

GULF OF MEXICO...

The Weather Prediction Center is issuing advisories on Tropical
Depression Nicholas, located over southern Louisiana. Refer to
the Special Features section above for details.

As previously mentioned, a surface trough extends from the cyclonic
circulation of Nicholas to near 24N94W. Gentle to moderate SE-S
winds are noted east of the trough, with gentle to moderate NW-N
winds west of the trough toward the Texas coast. Gentle to moderate
easterly winds are seen just N of the Yucatan peninsula. Seas are
2 to 3 ft across the basin, except 3 to 5 ft over the north-central
Gulf where part of the circulation of Nicholas remains. Isolated
to scattered showers and thunderstorms are noted over the eastern
Gulf.

For the forecast, Tropical Depression Nicholas inland north of
the area is forecast to become a remnant low today. Conditions
will continue to gradually improve offshore the Louisiana and
upper Texas coasts. For the remainder of the week, gentle to
moderate mainly southerly flow will dominate the Gulf waters under
the influence of a ridge.

CARIBBEAN SEA...

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

Recent satellite derived wind data show moderate to fresh trades
over the ABC Islands, near the entrance of the Gulf of Venezuela,
and in the Gulf of Honduras, with mainly gentle to moderate winds
elsewhere. Seas are 3-5 ft where the strongest winds are blowing
with 1-3 ft elsewhere.

Showers and thunderstorms continue to flare-up over the Greater
Antilles due to a combination of a tropical wave moving westward
across the basin and an upper-level low currently located just S
of eastern Cuba. A diffluent pattern aloft on the W side of the
upper-level low is also helping to induce convection over most of
Cuba and the NW Caribbean.

For the forecast, gentle to moderate winds will increase to
moderate to fresh today, with strong winds pulsing during the
overnights 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 situated northeast of the Bahamas, and the system in
the eastern Atlantic. Both systems have a high chance of tropical
cyclone formation through 48 hours.

A ridge dominates the Atlantic forecast waters E of 65W, with the
main high pressure center of 1028 mb over the Azores. A surface
trough continues to move westward across the tropical Atlantic and
extends from 24N36W to 16N37W. Mainly low clouds and limited
shower activity is noted near the trough axis. Scatterometer data
depicted very well the wind shift associated with the trough
axis. Moderate to fresh NE-E winds are noted near the northern
end of the trough. Fresh to strong N-NE winds are present off the
coasts of Morrocco and Mauritania, mainly east of 22W, due to the
pressure gradient caused by the ridge and lower pressures over
western Africa. Seas are in the 6 to 8 ft range across this area.

For the forecast, outside of the area of low pressure northeast
of the Bahamas, high pressure will lead to gentle to moderate
mainly easterly winds across the basin.

$$
GR
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