Marine Interpretation Message
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000
AGXX40 KNHC 221948
MIMATS

Marine Weather Discussion
NWS National Hurricane Center Miami FL
248 PM EST Wed Nov 22 2017

Marine Weather Discussion for the Gulf of Mexico, Caribbean Sea,
and Tropical North Atlantic from 07N to 19N between 55W and 64W
and the Southwest North Atlantic including the Bahamas

...GULF OF MEXICO...

A rather complex weather pattern continues over the gulf waters.
The latest surface analysis reveals A 1013 mb low over the NE
gulf near 28N85W with a cold front extending southwestward to a
1012 mb low at 26N88W. A trough extends from the 1012 mb low to
24N88W and continues southwestward to the SW gulf at 20N95W.
Behind these features, a cold front extends from Panama City
southwestward to 27N90W, to 26N94W to 23N96W and to inland Mexico
just north of Tampico. A vigorous short-wave trough rotating
through a very well pronounced longwave trough that stretches
from the NE U.S. southwestward to a cyclonic circulation diving
SSE over the NW Gulf at 26N95W, and continuing southwestward to
across southeastern Mexico and to eastern Pacific Ocean is
supporting these features that consist of of the complex weather
pattern. Strong high pressure is build southward over the western
gulf behind the front cold front. A very tight pressure gradient
between the high pressure and the cold front has resulted in a
large swath of strong to gale force northerly winds overtaking
the waters to the W of the cold front. A swath of NW gale force
winds has slipped southward within about 60-70 nm off the Mexican
coast ahead of the cold front to just northwest of the southern
end of the trough. This was nicely exhibited in the Ascat pass
from this morning.

Doppler Radar shows scattered showers and thunderstorms advancing
rapidly northeastward over the NE gulf waters. Latest satellite
imagery shows clusters of scattered showers and thunderstorms
over much of the gulf to the SE of a line from southeastern
Louisiana to 25N96W and to 19N96W. The activity over the western
gulf behind the front is being mainly sustained by instability
aloft generated by the cyclonic circulation at 26N95W.

As for the forecast, the low near 28N85W will lose its identity
through Friday while the one near 26N88W slowly tracks east-
northeastward to the far eastern gulf waters through early on
Friday before moving inland central Florida Friday afternoon
pushing the cold front to the far SE waters by late Saturday as
it weakens.

Wave model guidance suggests that combined seas will peak to a
maximum of around 14 ft in association with the gale force
conditions tonight before subsiding to around 10 ft early
Thursday night and to less than 8 ft early on Friday as high
pressure settles back over the entire area. The related pressure
gradient will bring generally moderate to fresh northerly flow
through Friday night and light to gentle northerly flow Saturday
through Sunday night, except for light anticyclonic flow over the
central gulf on Saturday and over the NW gulf on Sunday. Seas
will lower to 2-3 ft over the entire waters on Saturday, except
for the SE part of the gulf where seas will be slighter higher
in the 3-4 ft range due to a NW swell. These 3-4 ft seas will
subside to 2-3 ft during Sunday morning.

...CARIBBEAN SEA AND TROPICAL N ATLANTIC FROM 07N TO 19N BETWEEN
55W AND 64W...

A persistent surface trough is analyzed along 81W/82W from 11N to
21N. Scattered showers and isolated thunderstorms are seen
within 60 nm W of the trough from 11N to 14N, while isolated
showers and thunderstorms are elsewhere within 120 nm of the
trough. Latest moisture convergence model guidance indicates
that the trough will linger over the west-central Caribbean
through at least Friday. Scatterometer data detected a NE to SE
wind shift of mainly gentle winds across the trough axis, with
the exception of moderate northerly winds just off the coast of
Nicaragua. Moderate to locally fresh easterly winds are noted
over the eastern Caribbean, with mainly fresh winds off the coast
of Venezuela, including also the ABC Islands. Winds will
diminish over the S central and SE portion late this week as high
pressure N of the area weakens in response to the developing low
pressure along the east coast of the U.S. Seas will be quite
low, in the 2-4 ft range for the next few days. The weak pressure
gradient should remain in place over the Caribbean until
Thursday, when a cold front will enter the NW Caribbean from the
Gulf of Mexico. Model guidance indicates that the front will then
stall and weaken over the NW Caribbean Friday. The pressure
gradient between building high pressure over Central America and
the frontal boundary should bring an increase in northerly winds
of mostly 20 kt with possible pockets of 25 kt within about 120
nm off the Nicaragua coast Thursday night through Monday night
along with max combined seas of 6 or 7 ft. There is a possibility
that seas may reach 8 ft on Monday as suggest by the latest run
of the TAFB NWPS model output.

...SW N ATLANTIC INCLUDING THE BAHAMAS...

A ridge is now confined to the extreme NE waters. Interestingly,
a low has formed at 29N70W with a forming cold front extending
southwestward to the central Bahamas, and a developing warm
front that stretches southeastward to near 25N63W. The cold
front that was analyzed this morning over the NW portion of the
area has become diffused. The low is forecast to attain a fast
northeast motion later this afternoon and evening as deep
troughing to the W of the area progresses eastward. Latest
satellite imagery shows a large area of scattered moderate to
strong convection moving quickly eastward within 90 to 240 nm to
the E of the low. Models have been consistently noting that a
very tight pressure gradient will set up to the E and SE of the
low beginning this evening. This is expected to occur as the low
moves across the eastern part of zone AMZ115 near 29N67W early
tonight. So a gale warning was issued this morning within 150 nm
of the low in its southeastern semicircle where seas are forecast
to build to a maximum of about 14 ft. The low rapidly deepen as
it moves to just N of the forecast waters near 32N66W by early
on Thursday with a pressure of 1001 mb. The associated cold front
will extend from the low to 26N67W where it becomes stationary
to near eastern Cuba. The gale force southerly winds are expected
to be N of about 28N and E of 67W at that time, with seas of
8-11 ft. These conditions will exit zone AMZ115 during Thursday
afternoon.

Another low pressure system, currently over the eastern Gulf of
Mexico, will move across Florida and into the far NW waters
by late Friday morning. The associated cold front will move
across the western and central waters trough early Sunday
morning, and across the eastern and SE waters late Sunday through
Monday as it weakens to a frontal trough. Widespread showers and
thunderstorms with possible gusty winds are expected with both
the low and the cold front. Model guidance suggests that another
cold front will move across the NW portion on Saturday and across
the remainder of the waters into Monday followed by a large dome
of strong continental high pressure. Will have to watch as to
how future model guidance depicts the northerly winds behind this
next front as latest model suite is differing with respect to
this.

$$

.WARNINGS...Any changes impacting coastal NWS offices will be
coordinated through AWIPS II Collaboration Chat, or by
telephone:

.GULF OF MEXICO...
.GMZ011...NW GULF INCLUDING STETSON BANK...
   Gale Warning today for frequent gusts.
.GMZ013...N CENTRAL GULF INCLUDING FLOWER GARDEN BANKS MARINE
SANCTUARY...
    Gale Warning today W of 90W.
.GMZ017...W CENTRAL GULF FROM 22N TO 26N W OF 94W...
    Gale Warning today W of 96W.
.GMZ023...SW GULF S OF 22N W OF 94W...
     Gale Warning today into Thu.

.CARIBBEAN SEA AND TROPICAL N ATLANTIC FROM 07N TO 19N BETWEEN
55W AND 64W...
     None.

.SW N ATLANTIC INCLUDING THE BAHAMAS...
 AMZ115...N of 28N E of 67W through early Fri.

$$

*For detailed zone descriptions, please visit:
http://www.nhc.noaa.gov/abouttafbprod.shtml#OWF

Note: gridded marine forecasts are available in the National
Digital Forecast Database (NDFD) at:
http://www.nhc.noaa.gov/marine/grids.php

For additional information, please visit:
http://www.nhc.noaa.gov/marine

$$

.Forecaster Aguirre. National Hurricane Center.


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