Area Forecast Discussion
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FXUS62 KKEY 150958

Area Forecast Discussion
National Weather Service Key West FL
458 AM EST Thu Nov 15 2018

Water vapor imagery highlights a remarkable weather pattern across
the continental United States. A large and phasing mid-upper level
trough complex dominates the western two-thirds of the nation,
speckled with several short wave nodes adding to the complexity. A
lengthy moisture plume stretches from the eastern Pacific to the
northeastern US, then races east to near the Azores. The
subtropical ridging to the east of Florida has been eroded by a
westward moving mid-upper level TUTT-like cell. Surface
observations place a NNE to SSW oriented cold front over the
extreme southeastern Gulf of Mexico, the leading edge now
creeping into the Dry Tortugas. Ahead of the front, an arcing
cluster of showers and storms is moving northeast between the
Tortugas and the Lower Keys. Temperatures across the island chain
are in the lower 80s with dewpoints in the mid 70s. Aside from
northwest winds near 20 knots at Pulaski Shoal, most locations are
from the southeast to south and average less than 10 knots.

The cold front will spread east across the Florida Keys today,
reaching the Lower Keys this afternoon, and passing east of the
Upper Keys this evening. Locations behind the front can expect
strong northwest to north breezes, low level cloudiness, and
possibly a few sprinkles. Dewpoints will steadily fall this
afternoon and overnight, reaching the upper 50s on Friday. Coastal
shelf waters north of the island chain average 81 degF, which
will temper tonight`s lows. Nevertheless, temperatures should
fall to near or just below 70 after sunrise Friday morning.
Friday`s highs will struggle to reach the mid 70s, although
clearing skies and decreasing winds should allow most of the
island chain to reach 75 late in the afternoon. A mainland
density surge Friday night will resume a round of weak mesoscale
CAA, and lows should fall into the upper 60s for most island
communities. The last time the low temperature fell below 70 in
Key West was May 14. The long six months of summer are ending.
High pressure centered over the northern Gulf of Mexico and the
southeastern United States will maintain moderate northeast to
east breezes across the Florida Keys Saturday through Tuesday. The
cold front will lose momentum south of the Keys, and may try to
lift back across the island chain Saturday night or Sunday. A
reinforcing shot of cooler, drier air appears possible by


A Small Craft Advisory is in effect for all coastal waters west of
the Seven Mile Bridge. Northwest to north winds will increase to
20 to 25 knots across the affected coastal waters. Seas will
build to 9 to 11 feet across the deeper waters of the southeastern
Gulf of Mexico, up to 7 to 10 feet across the Straits of Florida
southwest of the Lower Keys, and up to 7 feet across the adjacent
coastal waters just west of the Marquesas Keys.

From synopsis, a strong, slow moving cold front over the Gulf of
Mexico will move southeast through the island chain today,
reaching the Dry Tortugas by sunrise, the Lower Keys in the early
afternoon, and the Upper Keys by early this evening. Strong
northerly breezes and building seas are expected behind the front.
Breezes will diminish on Friday, followed by moderate breezes
Saturday through Monday.


Mainly VFR conditions to prevail at the island terminals today,
but periods of MVFR to IFR ceilings/visibilities are possible
early in the forecast period. A line of showers and a few embedded
thunderstorms are approaching KEYW early this morning, with
several hours of MVFR to IFR conditions expected. Less confident
at KMTH where the line of showers is expected to break up as it
traverses the Middle Keys from 12-15z. Ceilings expected to slowly
improve afterwards, but could remain in the 030-040 range through
16/06. Main concern shifts from ceilings to winds late as gusty
northerly winds set in behind the cold front.


Key West  83  70  75  69 / 50 20 -  10
Marathon  85  69  75  68 / 50 20 -  10


GM...Small Craft Advisory for GMZ033>035- 044-054-055-074-075.



Data Collection......BT

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