[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 161041
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1205 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 0600 UTC surface analysis and satellite imagery through
1145 UTC.

...SPECIAL FEATURES...

Post-Tropical Cyclone Nicholas is centered near 29.4N 91.6W at
16/0900 UTC or 120 nm SSE of Alexandria Louisiana moving N at 2
kt. Estimated minimum central pressure is 1007 mb. Maximum
sustained wind speed is 20 kt with gusts to 25 kt. A trailing
trough is analyzed over the Gulf of Mexico and extends from 28N92W
to 22N94W. Nicholas 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 days as it struggles to develop minimal
thunderstorm activity near its center. Nicholas is expected to
produce additional rainfall amounts of 2 to 4 inches across the
central Gulf coast Friday, with isolated storm totals of 12 inches
possible. 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 30N74W 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 24N
to 33N between 67W and 73W. 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. 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 33W 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 noted from 05N to 18N and E of 23W
to the coast of Africa.

A tropical wave is in the Atlantic Ocean along 46W, from 04N to
17N, moving west at around 10 kt. Scattered showers are noted
where the wave meets the monsoon trough near 07N46W.

A tropical wave is in the Caribbean Sea along 74W from 20N
southward across the Windward Passage to Colombia, 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 along the trough axis
and near the coastal waters of Colombia.

A tropical wave is over Central America along 88W from 17N
southward across Honduras and western Nicaragua and into the
eastern tropical Pacific Ocean, moving west at 10 to 15 kt.
Scattered showers and thunderstorms are noted over the E Pacific.

...MONSOON TROUGH/ITCZ...

The monsoon trough emerges off the coast of Africa through
Senegal near 15N17W to 1011 mb low pressure located near 11.5N33W
to 07N51W. The ITCZ continues from 07N51W to the coast of Guyana
near 08N59W. Aside from the convection mentioned above, scattered
showers are noted in the vicinity of the trough.

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 22N94W. 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, Post-Tropical Cyclone Nicholas remains
stationary north of the area in SW Louisiana. Moderate to fresh
winds will gradually diminish improving conditions offshore the
Louisiana and upper Texas coasts today. For the remainder of the
week, gentle to moderate southerly flow will dominate the basin.

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 1026 mb over the Azores. A surface
trough continues to move westward across the tropical Atlantic
and extends from 26N37W to 17N39W. 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 Morocco 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.

$$
Torres
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