[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 201052
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1205 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 0600 UTC surface analysis and satellite imagery through
1045 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. Satellite imagery shows the overall
appearance of Nigel hasn't changed much since several hours ago.
Deep convection of the numerous moderate to strong type intensity
has recently formed north of the center from 34N to 36N. Similar
convection is within 150 nm of the center in the southern
semicircle. Nigel continues to exhibit a large eye feature, about
40 nm in diameter. Nigel is forecast to 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 gale force
north to northeast winds of 30-35 kt for the waters north of 30N
between 77W-79W on Thu and north of 29N on Thu night. Seas with
these winds are forecast to be 9 to 13 ft.

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 far eastern Atlantic tropical wave was introduced to the 06Z
surface analysis just offshore Africa near 20W from 03N to 19N.
It is moving westward at 10-15 kt. Scattered moderate to isolated
strong convection is within 180 nm east of the wave from 13N to
16N. Scattered moderate to isolated strong convection is within
60 nm either side of the wave from 10N to 12N. Scattered moderate
convection is within 120 nm east of the wave from 04N to 08N.
Environmental conditions are forecast to be conducive for
gradual development, and a tropical depression is likely to form
late this week or this weekend while the system moves generally
westward across the eastern and central tropical Atlantic.

An eastern Atlantic tropical wave has its axis extending from
near 18N32W to 11N34W and to 03N34W. It is moving westward at
10-15 kt. Increasing numerous moderate to isolated strong
convection is noted within 240 nm east of the wave from 04N
to 10N. Scattered moderate convection is within 120 nm west
of the wave from 06N to 14N.

A western Atlantic tropical wave has its axis near 49W from
03N to 16N. It is moving westward at 10-15 kt. Isolated small
showers and thunderstorms are near this wave.

...MONSOON TROUGH/ITCZ...

The monsoon trough axis extends off the coast of Senegal near
15N17W and continues southwestward to 09N26W, then westward to
10.5N46.5W. The ITCZ extends from 10N34W to 10N42W and to 10N49W.
Other than the convection described in the TROPICAL WAVES section
above, scattered moderate convection is seen within 120 nm
south of the trough between 43W-46W and within 690 nm south of
the trough between 40W-41W.

...GULF OF MEXICO...

A stationary front extends from near Sarasota, Florida
southwestward to 25N89W. A rather weak pressure pattern is over
the area. The gradient is allowing for gentle to moderate east to
southeast winds and seas of 2-4 ft north of the front. Light to
gentle winds and seas of 1-3 ft are found south of the boundary.
Scattered showers and thunderstorms are increasing along and
north of the front. A trough is over the western Gulf extending
from near 29N92W to 24N95W. Similar activity is between the front
and the trough. Isolated small showers and thunderstorms are over
the eastern Bay of Campeche.

For the forecast, the aforementioned stationary front will
will remain in place through Thu, then begin to move south as a
cold front late Thu through Fri night and to southeast of the Gulf
Sat as low pressure east of northern Florida lifts northward. The
front is expected to become stationary from western Cuba to the
Yucatan Channel Sun. Otherwise, high pressure will be in control
of the weather regime allowing for generally gentle to moderate
east to southeast winds along with 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 fresh NE winds 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 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 NW Venezuelan coasts. Seas
in the central Caribbean are in the range of 4-7 ft. Elsewhere,
light to gentle winds and seas of 2-4 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 trade winds in the central
Caribbean will be at mostly moderate speeds Thu through Sun, then
increase to fresh speeds Sun night as well as in the western part
of the eastern Caribbean. Gentle to moderate trade winds elsewhere
will continue through the period, for fresh to strong northeast
to east winds offshore northern Colombia and northwest Venezuela
that will diminish to fresh speeds Fri and to gentle to moderate
speeds Sat through Sun night. Gentle to moderate trade winds will
be elsewhere in the Caribbean through the next few days.

...ATLANTIC OCEAN...

Please read the SPECIAL FEATURES section for details on
Hurricane Nigel and on the recently issued ATLANTIC GALE WARNING.
In addition, please read the TROPICAL WAVES and MONSOON
TROUGH/ITCZ sections for convection in the tropical Atlantic.

A stationary front extends from near 31N70W to east-central
Florida. The combination of this front and a very sharp upper-
level trough over its vicinity is leading to widespread shower
and thunderstorm activity north of the front and between 74W-80W.
Numerous showers and thunderstorms, with frequent lightning
and shifting east-southeastward extends from the NW Bahamas
southwestward to just north of central Cuba.

A trough moving quickly westward is analyzed from 20N45W to
14N41W. This feature is supported by an upper-level low that is
near 20N46W. Scattered moderate convection is noted from 19N to
21N between 42W-47W. Scattered showers and isolated thunderstorms
are within 180 nm east of the trough from 16N to 19N.

Moderate or weaker winds and 2-4 ft seas are found behind the
frontal boundary. The remainder of the Atlantic is dominated by a
broad subtropical ridge positioned near the Azores, with a 1021 mb
high center near 33N23W. The pressure gradient between the
aforementioned 1021 mb high pressure system and lower pressures in
the deep tropics support fresh to strong easterly winds east of
50W and north of 16N. Seas in these waters are 6-9 ft in mixed
northeast and northwest swell. Seas of 9-12 ft created by
Hurricane Nigel are north of 30N between 51W-58W, and this is
where strong south-southwest and west to northwest winds in the
most outer southern fringes of Nigel are found as well. These
conditions will shift north of 31N by early tonight. Elsewhere,
moderate or lighter winds and moderate seas continue.

For the forecast W of 55W, Hurricane Nigel is north of the area
near 34.2N 54.9W at 5 AM EDT, and is moving north at 14 kt.
Maximum sustained winds are 85 kt with gusts to 105 kt, and the
minimum central pressure is 971 mb. Nigel is forecast to
accelerate northeastward later today as it pulls farther away from
the area. Strong winds and seas 12 ft or greater north of 30N
over the northwest part of the area will lift north of 31N later
this morning. The stationary front that extends 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.

Aguirre
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