Area Forecast Discussion
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FXUS62 KKEY 280241

Area Forecast Discussion
National Weather Service Key West FL
1041 PM EDT Thu Oct 27 2016

Changes to Forecasts -- We reduced rain chances overnight, and
made small adjustments to the digital database, mainly to qpf,
sky cover, winds, wave heights, and temperature elements.

Current Situation and Analysis -- Some fairly impressive lower-
tropospheric winds were revealed by data collected from the Key West
evening radiosonde balloon, with a surface-to-10000-ft layer mean
wind of 075/035 knots.  Sustained winds at the surface have been a
little lower, ranging from 20 to 30 knots depending on location and
exposure.  However, numerous passing showers, squalls, and even a
few thunderstorms transferred momentum to the surface in gusts,
especially earlier this evening, when numerous reports in the range
of 35-40 knots were received from various stations up and down the
Keys and adjacent reefs.  Overall rain coverage has decreased during
the last hour or so.  However, showers have been quick-forming and
fast-moving, and another cluster recently has developed around the
upper Keys, and is moving rapidly westward.  The clouds and rain
kept air temperatures down for most of the day, with highs in most
island communities in the upper 70s or near 80F.  Current air
temperatures are mostly in the mid 70s, with dewpoint temperatures
near 70F.  We owe the unsettled weather pattern to a sharp, and, as
it turns out, fairly deep and somewhat complex trough/cyclonic
vorticity pattern between the Gulf coast and the Caribbean, with
a healthy infusion of moisture from the lower troposphere thanks
to a high-momentum near-surface layer and a favorably positioned
upper jet streak.

Prognostic Overview -- It looks like cloud cover and rain chances
will be generally higher than average through Saturday night, with
gradual clearing Sunday-Monday.  However, stronger forcing for
ascent has diminished temporarily, and should increase again in
about 18-24 hours, peaking Friday night and Saturday.  We have
updated forecasts to lower rain chances somewhat for the overnight

A Small Craft Advisory remains in effect for all Florida Keys
coastal waters zones.  Sustained northeast to east winds of 20 to
30 knots with occasional gusts of 35 knots are expected overnight.
Seas will remain as high as 8 feet across portions of the extreme
southeastern Gulf of Mexico beyond five fathoms, while seas of 9 to
12 feet persist in the Straits of Florida.  Higher and steeper waves
will occur in the Gulf Stream, where wind-generated waves oppose
the current.  An expansive high pressure system will persist over
the southeastern United States overnight through Tuesday.  This
setup will maintain strong northeast to east breezes across Florida
Keys coastal waters.

VFR conditions will prevail overnight at both EYW and MTH.  Short-
lived MVFR/IFR ceilings and visibilities will return again after
about 28/15Z, with periodic MVFR or lower conditions likely at EYW
and MTH, mainly in fast-moving showers and isolated thunderstorms.
Through 28/12Z, sustained northeast to east (070 degrees) surface
winds will average 12-15 knots, with gusts 20-25 knots.

GM...Small Craft Advisory in effect for GMZ031-GMZ032-GMZ033-GMZ034-


Data Collection......Chesser

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