[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 201508
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1805 UTC Wed Sep 20 2023

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
1500 UTC.

...SPECIAL FEATURES...

Hurricane Nigel is centered near 34.4N 54.9W at 20/0900 UTC or
510 nm ENE of Bermuda, moving N at 14 kt. Estimated minimum
central pressure is 971 mb. Maximum sustained wind speed is 85
kt with gusts to 105 kt. Peak seas N of our area are currently
around 36 ft. Numerous moderate to strong convection is evident
within 270 nm in the S semicircle and 180 nm in the N semicircle
of Nigel. A turn toward the northeast with an increase in forward
speed is expected later today. Nigel has likely reached its peak
intensity, with gradual weakening expected later today, followed
by faster rate of weakening on Friday. Nigel is forecast to become
a post-tropical cyclone by Friday. Swells generated by Nigel will
affect Bermuda during the next couple of days. These swells are
likely to cause life-threatening surf and rip current conditions.
Please consult products from your local weather office.
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 Nigel
NHC Forecast/Advisory and Public Advisory at www.hurricanes.gov
for more details.

Atlantic Gale Warning: The pressure gradient between low
pressure that is expected to develop along a stationary front
over the northwest part of the SW N Atlantic and high pressure
over the southeastern U.S. is expected to result in frequent gusts
to gale force N of 30N and W of 77W starting Thu evening, then N
of 29N and W of 77W Fri morning. Seas with these winds are
forecast to be 7-10 ft and could be locally higher. Please see
the latest NWS High Seas Forecast issued by the National Hurricane
Center at website https://www.nhc.noaa.gov/text/MIAHSFAT2 for
further details.

...TROPICAL WAVES...

A tropical wave is in the far eastern Atlantic Ocean along 19N/20N
from 19N southward just SE of the Cabo Verde Islands, moving
slowly W around 5 kt. Scattered moderate to strong convection is
evident from 12N to 16N between 18W and 22W. Scattered moderate
convection is evident from 05N to 11N between 16W and 23W.

A tropical wave is moving from the eastern to the central Atlantic
Ocean along 35W from 19N southward, moving slowly W around 5 kt.
Scattered moderate to strong convection is evident from 09N to 15N
between 34W and 39W, and from 02N to 09N between 30W and 41W.

A tropical wave is approaching the tropical N Atlantic waters
along 49W/50W from 16N southward to just off the coast of far NE
Brazil, moving slowly W around 5 kt. No significant convection is
evident near this tropical wave.

...MONSOON TROUGH/ITCZ...

The monsoon trough axis extends off the coast of Senegal near
14N17W to 09N27W to 10N39W to 09N47W. The ITCZ axis extends from
09N51W to across Guyana near 08N60W. Nearby significant convection
is discussed in the Tropical Waves section above.

...GULF OF MEXICO...

A stationary front is dissipating from near Fort Myers, Florida to
25N88W. Scattered showers and thunderstorms are occurring mainly N
of the boundary to the NE Gulf coast. Moderate easterly winds are
N of the front with mainly gentle winds elsewhere across the
basin. Satellite imagery indicated a 1010 mb low pressure are in
the NW Gulf near 27N95W with a trough extending ENE to 28N90W.
Scattered thunderstorms are S of this, from 24N to 27N between 90W
and 93W. A weak surface trough is noted in the Bay of Campeche.
Seas are 1-3 ft across the basin, locally 4 ft in the NW Gulf near
the low per nearby observations.

For the forecast, high pressure will be in control of the weather
regime across the Gulf waters allowing for generally gentle to
moderate east to southeast winds and slight seas, except pulsing
to moderate to fresh offshore the western Yucatan Peninsula in the
evenings. Developing low pressure east of Florida will tighten
the pressure gradient over the NE Gulf bringing moderate to
locally fresh NE winds across the NE Gulf Thu night into Fri. A
frontal trough associated with the aforementioned low pressure
will move across the SE Gulf and the Straits of Florida Thu night
into Fri.

...CARIBBEAN SEA...

Divergent flow associated with an upper-level trough located in
the NW Caribbean Sea acting on abundant tropical moisture
continues to support widely scattered moderate convection in the
NW Caribbean. A weak pressure gradient sustains mainly moderate to
fresh easterly trade winds in the central Caribbean. However,
strong winds are occurring just off the N Colombia and NW
Venezuelan coasts. Seas in the central Caribbean are in the range
of 4-7 ft. Elsewhere, gentle to moderate winds and seas of 2-5 ft
prevail.

For the forecast, long period north to northeast swell moving
through the Tropical N Atlantic waters and Caribbean passages will
subside Thu. Moderate to fresh trades will prevail in the south-
central Caribbean, locally strong at times offshore northern
Colombia and northwest Venezuela, with moderate or weaker winds
elsewhere through the week.

...ATLANTIC OCEAN...

Please read the Special Features section for details on Hurricane
Nigel and on an Atlantic Gale Warning. In addition, please read
the Tropical Waves and Monsoon Trough/ITCZ sections for details on
convection in the Atlantic Ocean.

A stationary front extends from 31N68W to near Fort Pierce,
Florida. The combination of this front and a very sharp upper-
level trough over its vicinity is leading to widespread shower and
thunderstorm activity from 22N to 31N between 72W and 80W.
Moderate to fresh NE winds are N of the front. A few weak troughs
are analyzed elsewhere W of 55W, otherwise weak ridging prevails N
of 20N and E the front with Nigel continuing to lift N away from
the area. Another weak trough is noted from 22N46W to 16N42W.
Scattered moderate convection is noted from 18N to 21N between 43W
and 47W. Moderate to fresh trades are evident from 17N to 27N
between the coast of Africa and 50W between a ridge N of that area
and three tropical waves along the monsoon trough/ITCZ. Seas are
7-9 ft there. Across the remainder of the basin, gentle to
moderate winds and 4-7 ft seas prevail, except 7-10 ft seas in
northerly swell related to Nigel N of 28N between 48W and 65W.

For the forecast W of 55W, moderate to fresh winds and seas of up
to 11 ft mainly N of 29N and E of 60W will move N of area by this
evening. A stationary front extending from near 31N70W to east-
central Florida will change little through Thu. The frontal
boundary should begin to slowly lift northward on Fri as low
pressure develops along it to the east of northern Florida, where
gale conditions and rough seas are possible Thu night into Fri.
This non-tropical area of low pressure could acquire some
subtropical characteristics by this weekend while it moves
generally northward. Regardless of development, this low is likely
to bring gusty winds to gale force, heavy rain, and high surf to
portions of the Southeast and Mid-Atlantic United States late this
week and into this weekend.

$$
Lewitsky
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