[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 172313
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0005 UTC Sat Dec 18 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
2300 UTC.

...MONSOON TROUGH/ITCZ...

The monsoon trough is confined to the African continent. The ITCZ
begins near the coast of Sierra Leone near 07N13W and continues to
05N25W to 07N40W to the coast of NE Brazil near 03N51W. A surface
trough is within the ITCZ and extends from 12N35W to 05N38W.
Fresh NE to E winds are near the northern end of the trough axis.
Scattered moderate convection is noted from 03N-06N between 28W
and 33W.

GULF OF MEXICO...

High pressure of 1027 mb located E of Bermuda near 31N59W extends
a ridge across Florida into the Gulf of Mexico producing a gentle
to moderate E to SE wind flow across much of the basin. Moderate
to locally fresh SE winds are noted over the western Gulf with
mainly fresh easterly winds in the Straits of Florida. Seas are
generally 3-5 ft across the Gulf waters, except for seas up to 6
ft in the SE Gulf and Florida Straits. A diffluent pattern aloft
supports scattered showers and isolated thunderstorms over the NE
Gulf, particularly N of 25N and E of 88W.

For the forecast, a ridge will prevail through Sat, supporting
moderate to locally fresh SE to S winds. A cold front is forecast
to enter the basin Sat night. Fresh to strong N to NE winds and
building seas will prevail west of the front on Sun. By Mon, low
pressure should develop along the cold front in the central Gulf
and steadily progress east-northeastward, pulling the front
across the Gulf by Tue. Winds and seas across the basin should
slowly subside on Wed.

CARIBBEAN SEA...

The tight pressure gradient between high pressure located E of
Bermuda and the Colombian/Panamanian low is resulting in strong
to near gale-force trades across the central Caribbean Sea, with
the strongest winds occurring offshore NW Colombia. Satellite
derived wind data show near gale-force trades within about 120 nm
of NW Colombia while an altimeter pass indicates seas of up to
12 ft. Fresh to locally strong winds are present across the
remainder of the E and central Caribbean, particularly near Cabo
Beata, Dominican Republic. Moderate to fresh NE to E winds are
seen over the NW Caribbean, including the lee of Cuba. Seas of
9-12 ft are present in the central Caribbean, with seas of 6-8 ft
in the eastern Caribbean, and 4-6 ft in the NW Caribbean.

Low-level convergence continues to enhance the development of
scattered showers and isolated thunderstorms in the SW Caribbean
Sea, mainly W of 80W, including the Caribbean plains of Nicaragua.
A few showers are also noticed in the Gulf of Honduras, affecting
the Bay Islands. Patches of low level moisture, embedded in the
trade wind flow, are observed elsewhere producing isolated to
scattered passing showers.

For the forecast, the strong high pressure located E of Bermuda
will prevail over W Atlantic through late Sun. This will support
fresh to strong tradewinds over the central and E Caribbean and
tropical N Atlantic waters. From Mon through Wed, a developing
low pressure along a frontal boundary off of the SE United States
coast will act to weaken the trade winds across the area. Large
N to NE swell reaching the tropical N Atlantic as well as Mona
and Anegada Passages tonight will continue through Mon.

ATLANTIC OCEAN...

The above mentioned high pressure located E of Bermuda dominates
the western Atlantic, the Bahamas and the State of Florida.
Farther E, a cold front enters the forecast waters near 31N26W
then continues SW to near 20N47W. A shearline begins at 20N47W
and stretches westward to near 20N64W. A belt of fresh to strong
NE to E winds is noted between the high pressure and the
shearline, mainly from 20N-25N between 40W-75W. Seas are 8-12 ft
within this area of winds. An altimeter pass indicates seas of up
to 15-16 ft in the wake of the front, roughly between 40W-50W.
Low level clouds with possible showers are associated with the
frontal boundary. The pressure gradient between the strong high
and lower pressures in the vicinity of the ITCZ also supports
fresh to locally strong NE-E winds from 10N-20N between 40W and
the Lesser Antilles. Seas of 8-11 ft in NE swell are in this
region.

For the forecast, the Bermuda High will build southward, bringing
an increase in winds and seas during the weekend. On Mon, a strong
cold front will move off of SE United States coast ahead of a
developing low pressure on Tue. Winds on both sides of the cold
front are anticipated to reach strong or near gale force north
of 27N on Wed. Large N swell impacting the Atlantic zone from
19N-22N between 55W-65W will diminish on Sun.

$$
GR
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