[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 200600
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0605 UTC Sun Dec 20 2020

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 32N. The following information is based on satellite
imagery, weather observations, radar and meteorological analysis.

Based on 0000 UTC surface analysis and satellite imagery through
0545 UTC.

...MONSOON TROUGH/ITCZ...

The monsoon trough axis extends from the coastal sections of
Sierra Leone near 09N13W to 06N17W, where latest scatterometer
data indicates that is transitions to the ITCZ to 06N18W and
continues to 05N30W to 05N40W and to the coast of Brazil near
04N51W. Scattered moderate to isolated strong convection is
within 120 nm north of the ITCZ between 33W-38W and within 60 nm
north and south of the ITCZ between 28W-33W. Scattered moderate
convection is well to the south of the monsoon trough within 30
nm of line from 04N10W to 04N18W, and also within 180 nm north of
the ITCZ between 38W-44W.

GULF OF MEXICO...

A positively-tilted upper shortwave trough stretches from eastern
Arkansas southwestward to eastern Texas. This feature is driving
a a cold front that as of 03Z extends from a 1014 mb low at
29N92W, or about 60 nm southwest of Morgan City, Louisiana
southwestward to 25N95W and to inland Mexico at 23N98W. A rather
vigorous pre- frontal squall line is along a position from near
Terrebonne Bay, Louisiana to 27N93W and to near 24N95W. Current
NWS mosaic Doppler Radar imagery shows scattered moderate to
isolated strong convection is along and within 60-90 nm east of
the squall line north of 27N and also along and within 60 nm east
of the squall line from 24N-27N. This activity is capable of
producing strong gusty winds and numerous lightning strikes.

East of both the cold front and squall line, high pressure ridging
extends from a 1029 mb high pressure center that is located along
the Delmarva Peninsula southwestward to the eastern Gulf. The
gradient between the high pressure and lower pressure over the
western Gulf near the squall line and cold front is allowing for
generally gentle to moderate east to southeast winds over the area,
with the exception of moderate to fresh southeast winds over the
NW and north central Gulf waters as seen in the latest and current
buoy observations as well in a partial ASCAT pass from last night.
Stronger winds, up to near gale force and southerly in direction,
were revealed in the 0244Z ASCAT to be associated with convection
ahead of the front along and east of the squall line.

Seas are in the range of 3-5 ft, except for higher seas of 4-6 ft
in the NW Gulf. Seas near aforementioned convection may be tough.

As for the forecast: The high pressure over the eastern Gulf
will continue to shift eastward through Sun night in the response
to eastward advancement of the low pressure and cold front. The
front is forecast to reach from the central Gulf Coast to the
western Bey of Campeche on Sun, and from southwest Florida to the
Yucatan peninsula on Mon before exiting the southeastern Gulf
early on Mon. Expect for the present ongoing shower and
thunderstorm activity to gradually shift to the eastern Gulf
today and tonight. Moderate to fresh southeast winds are expected
in the NW Gulf on Wed. By Thu, a strong cold front is forecast to
move across the basin, with the possibility of gale force
northwest to north winds following in behind it over the SW and
west-central Gulf waters.

CARIBBEAN SEA...

Latest scatterometer data revealed fresh to strong northeast to
east winds over the south-central Caribbean. Fresh northeast
winds are present south of Hispaniola and over the Windward
Passage. These winds are the result of a tight gradient between
high pressure that is located well north of the area along the
U.S. Mid-Atlantic coast and lower pressure that is typically over
NW Colombia and southwestern Caribbean Sea. These winds will
continue into this morning as the high pressure remains in place.
Winds are then forecast to diminish across the basin later on Sun
as the high pressure shifts northeastward.

Shallow low-level moisture in the form of scattered to broken low
clouds is embedded in the trade wind flow, mainly north of about
14N. Isolated showers are possible with some of these clouds,
except for scattered showers that are confined to the Gulf of
Honduras, over the interior of Honduras and in some interior
sections of Jamaica. An area of scattered to broken low and mid-
level clouds is noted over the extreme southeastern Caribbean
south of 13N and east of 64W. Surface observations from some of
the Windward Islands indicate scattered light showers over and
near that general area. Northeast winds over the Bahamas, and the
Old Bahama Channel are also advecting patches of low-level
moisture with possible isolated into eastern Cuba as well as
sections of central Cuba.

As for the forecast: A weakening stationary front over north-
central Cuba will dissipate overnight tonight. The gradient
associate to high pressure north of the area will support mostly
fresh northeast trade winds across much of the area through Thu.
Highest winds and seas will continue to be in the southern
Caribbean, near the coast of Colombia, through Wed night. A cold
front will slide southward into the northwestern Caribbean on
Tue, stall across the region on Wed and dissipate by Thu.

ATLANTIC OCEAN...

A cold front extends from near 32N47W southwestward to 25N59W,
where it transitions to a stationary front to 22N75W and
dissipating to along the north-central coast of Cuba. A pretty
extensive field of cold-air stratocumulus clouds is observed
behind the frontal boundary, while broken low and mid-level
clouds with mainly scattered showers are along and within 60 nm
southeast and south of the frontal boundary, except for isolated,
small and weak thunderstorms between 63W-67W. Mainly moderate
northerly winds are noted in the wake of the front, with an area
of fresh winds just to the north of the southeastern Bahamas as
were detected by an ASCAT pass from last night. Strong high
pressure is building in over the western Atlantic behind the
front.

A ridge prevails over the east Atlantic, anchored by a 1026 mb
high pressure center located near 30N26W. Fresh trade winds are
along the southern periphery of the ridge affecting the Cabo
Verde Islands and regional waters were seen in a partial ASCAT
pass from last night.

As for the forecast: The aforementioned cold front will continue
to push eastward and dissipate on Mon. The next cold front will
move off the Florida coast on Mon, reach the southern Bahamas and
southern Cuba by Tue, and continue moving eastward on Wed. Strong
to near gale force winds are forecast to develop ahead and behind
this next front off the Florida coast and north of the Bahamas on
Mon through Tue. By the end of the week, a strong cold front will
push off the northeast Florida coast enhancing winds and
convection.

$$
Aguirre
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