[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 150006
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0005 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 1800 UTC surface analysis and satellite imagery through
2000 UTC.

...SPECIAL FEATURES...

Tropical Depression Nicholas is centered near 29.9N 94.4W at
14/0000 UTC or 20 nm W of Port Arthur Texas moving ENE at 5 kt.
Estimated minimum central pressure is 1003 mb. Maximum sustained
wind speed is 30 kt with gusts to 40 kt. Scattered moderate to
strong convection is noted over the Gulf of Mexico within 30N93W
to 30N84W to 24N90W to 23N96W to 26N97W to 28N93W to 30N93W.
Peak seas over the NW Gulf of Mexico are 10 to 11 ft, mainly
within the coastal waters between SW Louisiana and eastern
coastal Texas. Nicholas will weaken to a tropical depression Wed
morning, become a remnant low Thu morning, and dissipate Fri
afternoon. By tonight, winds over the waters of the NW and N-
central Gulf of Mexico will diminish to 20 kt or less and seas
will subside to 8 ft or less. Heavy rainfall through Wed night
is likely to cause some flooding across portions of southern and
central Louisiana, southern Mississippi and far southern
Alabama. Please read the latest High Seas Forecast issued by the
National Hurricane Center at website
https://www.nhc.noaa.gov/text/MIAHSFAT2.shtml and the latest
Nicholas NHC Forecast/Advisory and Public Advisory at
www.hurricanes.gov for more details.

A far eastern Atlantic tropical wave has an axis along 22W from
01N to 19N, moving west at 20 kt. A 1009 mb low pressure is along
the tropical wave axis near 10.5N22W, or a few hundred nm south-
southeast of the Cabo Verde Islands. Scattered moderate and
isolated strong convection is noted from 10N to 12N between 21W
and 24W, from 02N to 07N between 14W and 20W, and from 04N to 10N
between 22W and 28W. The associated showers and thunderstorms
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
system moves generally westward at about 15 kt 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 30N69W to 20N73W near the approach
to the Windward Passage, and a couple of hundred nm northeast of
the southeastern Bahamas. This is a deep layer trough that extends
from the surface to the upper-levels. Scattered moderate and
isolated strong convection is noted from 21N to 21N between 62W
and 75W. Environmental conditions are forecast to be conducive
for gradual development during the next few days, and a tropical
depression could 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 26N
between 70W and 75W through Thu. 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 22W.

A tropical wave is in the Atlantic Ocean along 40W/41W from 03N to
17N, moving west at around 10 kt. No significant convection is
noted with this tropical wave, however scattered showers are
noted from 03N to 17N between 38W and 46W.

A tropical wave is in the eastern Caribbean Sea along 65W, moving
west at around 15 kt. Isolated moderate convection is noted from
13N to 17N between 64W and 69W, with scattered thunderstorms
also noted over the U.S. Virgin Islands, Puerto Rico, Hispaniola
and the northern coast of Venezuela.

A tropical wave is in the western Caribbean Sea along 81W from 18N
southward to across western Panama and into the eastern Pacific
Ocean, moving west at 15 to 20 kt. Isolated moderate to strong
convection is noted from 10N to 14N between 77W and 84W, with
additional activity noted over nearby land locations due to
afternoon heating.

...MONSOON TROUGH/ITCZ...

The monsoon trough emerges off the coast of Senegal near 14N17W
to 1009 mb low pressure near 10.5N22W to 13N32W to 08N46W. The
ITCZ continues from 08N46W to the NE coast of Venezuela near
9.5N61W. Aside from the convection mentioned above, scattered
moderate convection is noted from 10N to 12N between 57W and 59W.

GULF OF MEXICO...

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

Otherwise, gentle to moderate SE-S return flow dominates the basin
outside of the outer effects of Nicolas. Seas are in the 2 to 4 ft
range east of 90W, and 3 to 6 ft range west of 90W outside of the
NW and N-central Gulf.

For the forecast, Tropical Storm Nicholas will weaken to a
tropical depression near 29.8N 94.0W Wed morning. Tropical storm
conditions will remain over the SE Texas and SW Louisiana coastal
waters through early this evening. Fresh to strong winds will
diminish to moderate to fresh tonight and then prevail over the
north-central waters through Wed afternoon. For the remainder of
the week, gentle to moderate return flow will dominate across the
basin.

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 isolated thunderstorms over the north-
central Caribbean Sea. Gentle to moderate trades prevail across
the basin, along with seas in the 2 to 4 ft range, except 1 to 3
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 Wed
night, moderate to fresh winds will develop in the Gulf of
Honduras and eastern half of the Caribbean. Winds will further
increase to fresh to strong in the Gulf of Honduras and the S-
central basin Thu night, continuing through Sat.

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.

Elsewhere, a surface trough extends from 22N29W to 13N34W.
Another surface trough is from 23N47W to 20N26W. Limited shower
activity is noted near the troughs. Moderate to fresh winds are
noted west of the eastern trough from 16N to 24N to 35W. Gentle
to moderate winds dominate the entire rest of basin due to a weak
sub-tropical surface ridge. Seas are in the 3 to 5 ft range west
of 35W, and 4 to 6 ft range east of 35W.

For the forecast west of 55W, 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 the troughing that extends to the Turks and Caicos.

$$
Lewitsky
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