[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 141802
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1805 UTC Tue Sep 14 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
1700 UTC.

...SPECIAL FEATURES...

At 14/1800 UTC, Tropical Storm Nicholas is centered near 29.4N
95.0W, or about 25 nm SE of Houston Texas, and about 10 nm NW of
Galveston, moving ENE at 6 kt. Estimated minimum central
pressure is 1003 mb. Maximum sustained wind speed is 35 kt with
gusts to 45 kt. Scattered moderate to strong convection is
within 300 nm of the center in the eastern and southern
quadrants, including portions of SE Louisiana and the northwest
Gulf of Mexico. Scattered moderate showers are elsewhere within
360 nm of the center in the E semicircle, including over
portions of southern Mississippi and the north-central Gulf of
Mexico. Peak seas over the northwest Gulf of Mexico are 13 ft as
of 14/1200 UTC. The storm should move more slowly toward the
east-northeast through tonight, and then turn eastward on
Wednesday over Louisiana. Nicholas is forecast to weaken to a
tropical depression tonight. By tonight, winds over the waters
of the NW and north-central Gulf of Mexico will diminish to 25
kt or less and seas will subside to 8 ft or less. Heavy rainfall
through Wednesday 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 20/21W
from 03N-18N, moving W at 15 kt. A 1009 mb low pressure is along
the wave axis near 10N 20.5W. Scattered moderate convection is
seen from 03N-15N between 13W-26W. Associated shower and
thunderstorm activity near the low pressure continues to show
signs of organization, and environmental conditions are
conducive for a tropical depression to form during the next
couple of days while the system continues westward. This system
has a high chance of tropical cyclone formation within 48 hours.
Please see the latest Tropical Weather Outlook at
www.hurricanes.gov for more details.

A surface trough extends from 20N72W to 28N69W. This is a deep
layer trough that extends from the surface to the upper-levels.
Scattered moderate and isolated strong convection prevails from
20N-30N between 63W-74W. An area of low pressure is expected to
form along the trough during the next day or two a couple of
hundred nm north of the southeastern or central Bahamas. Some
gradual development of this system is forecast thereafter, and a
tropical depression could form later this week while the system
moves north-northwestward or northward across the western
Atlantic, in between Bermuda and the east coast of the United
States. The chance of tropical cyclone formation during the next
48 hours is medium. Regardless of development, increased winds
and seas are expected north of 26N between 70W-75W Wed and Thu.

...TROPICAL WAVES...

An Atlantic Ocean tropical wave has an axis along 40W from
04N-16N, moving W at 15 kt. Isolated to scattered showers are
within 120 nm either side of the wave axis from 06N-15N.

An eastern Caribbean Sea tropical wave has its axis along
63/64W, moving W at 15 kt. Isolated moderate convection is noted
within 210 nm either side of the wave axis from 13N-20N,
including near the northern Leeward and Virgin Islands. The wave
combined with an upper-level low spinning over Hispaniola will
support showers and thunderstorms over the U.S. Virgin Islands,
Puerto Rico and Hispaniola tonight and Wed.

Another tropical wave in the Caribbean Sea has an axis along 79W
from 19N southward, moving W at 10-15 kt. Scattered moderate and
isolated strong convection is observed within 120 nm of the wave
axis from 10N-13N.

...MONSOON TROUGH/ITCZ...

The monsoon trough emerges off the coast of The Gambia near
13N17W to low pressure 1009 mb near 10N 20.5W to 10N25W, where
there is a break in the monsoon trough. The monsoon trough
continues from 11N38W to 08N46W. The ITCZ extends from 08N46W to
09N60W. Aside from the convection mentioned above, scattered
moderate showers are noted along and within 150 nm N of the ITCZ
between 55W-59W.

GULF OF MEXICO...

Tropical Storm Nicholas is weakening, centered near Houston
Texas. However, the effects of Nicholas continue to dominate the
Gulf of Mexico north of 25N and west of 88W. Nicholas will
continue to move inland and weaken to a tropical depression near
30.1N 94.7W this evening. Winds and waves over the northwest
Gulf will improve tonight to values of 25 kt or less and 8 ft or
less, respectively. Then, moderate to fresh winds will continue
over the north-central waters through early Wed evening. See
above for more on Nicholas. Moderate SE winds currently prevail
over the eastern and southern Gulf of Mexico with seas of 2 to 3
ft. For the remainder of the week, gentle to moderate return
flow will dominate across the basin.

CARIBBEAN SEA...

Please see the Tropical Waves section for details on the
tropical waves moving across the Caribbean Sea.

An upper-level low is centered over Hispaniola, enhancing
scattered showers and isolated tstorms over the north-central
Caribbean Sea. A recent ASCAT pass shows gentle to moderate
trades across the basin. Seas of 2 to 4 ft prevail, except 1 to
3 ft over the NW Caribbean Sea.

For the forecast, showers and tstorms will continue near the
tropical waves into Wed. Gentle to moderate winds will continue
through Wed as a weak pressure gradient remains in place. 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
south-central basin Thu night, continuing through Sat.

ATLANTIC OCEAN...

See the Special Features section above for details on the system
in the far eastern tropical Atlantic that has a high chance of
tropical cyclone formation, and on the system in the western
Atlantic, that has a medium chance of development within the
next 48 hours.

Elsewhere, a surface trough extends from 12N35W to 22N28W.
Another surface trough is from 21N42W to 24N46W. Little to no
shower activity and moderate wind speeds are observed near these
two troughs. Gentle to moderate winds dominate the entire basin,
due to a weak subtropical surface ridge. Seas are 3-5 ft.

$$
Hagen
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