Area Forecast Discussion
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FXUS62 KKEY 240856

Area Forecast Discussion
National Weather Service Key West FL
456 AM EDT TUE MAY 24 2016

Changes to Forecast -- Winds and wave heights were increased from
late tonight through Thursday night.  Isolated/slight chance of
thunderstorms were indicated for today through Wednesday night.
Slight adjustments were made to sky cover and some of the temperature

Current Situation and Analysis -- Analysis of satellite moisture
channel animations early this morning reveals a large cyclonic gyre
spinning along the mid-Atlantic coast...with cyclonic flow extending
all the way south to the Florida Keys and Bahamas.  A maritime
tropical air mass topped by rather steep mid-level lapse rates is
yielding a very unstable thermodynamic stratification across most of
the Bahamas...Straits of Florida...and extreme southern Florida.
Nevertheless...lower-tropospheric flow is quite weak...and
significant large-scale forcing for ascent is located well north or
east of the service area.  However, overnight we have observed
thunderstorms initiating readily along available boundaries.  Recent
Doppler radar data show thunderstorms across the Straits of Florida
between the upper Keys and the Bahama Banks, as well as recent
thunderstorm development over the Gulf-side beaches and flats north
of the lower Florida Keys, between Stock Island and Snipe Point.
Currently, air temperatures in most Florida Keys island communities
are between 75 and 80F, with dewpoint temperatures in the mid 70s.

Prognostic Overview -- The synoptic situation will be slow to change
during the next few days.  The most significant adjustment will be
the intensification of a surface high pressure cell beneath the
upstream short-wave ridge adjacent to the large cyclonic gyre.
This evolution will result in freshening northeast to east breezes
across Keys coastal waters.  Isolated to scattered showers and a
few thunderstorms will be a good bet through Wednesday night, when
perhaps some drier and more stable air will develop across the
region.  Forecast confidence is below average for the Thursday
through Monday time frame due to uncertainties associated with
surface cyclone structure and evolution over the South Atlantic
Bight region and associated gradient flow vectors and resulting
surface wind speeds and low-level boundary paths and subsequent
convective rainfall patterns across mainland South Florida and the
Florida Keys.

Winds and seas will be higher in and near isolated thunderstorms
today.  A high pressure system will build across the subtropical
North Atlantic, Florida Peninsula, and eastern Gulf of Mexico today
and tonight.  This will result in freshening northeast to east
breezes across Florida Keys coastal waters.  The high pressure
area will weaken and move northward from Wednesday through

An Airport Weather Warning for lightning within 5NM of EYW is in
effect through 24/0915Z.  Thereafter, expect VFR conditions this
morning thru about 18Z.  After 18Z, expect scattered clouds with
bases aoa FL020-025 & FL050-070 respectively, but short period
mvfr/ifr cigs and/or visibility will be possible in any showers
or storms that develop along a cumulus/towering cumulus cloud
line, in the vicinity of EYW and MTH.  Surface winds will be
variable at 6 knots or less, becoming east at 5 to 10 knots by 18Z.

The Key West daily record rainfall is 3.15 inches, recorded on
24 May 1937.  Daily record high, cold high, warm low, and low
temperatures are 92 in 1873, 78 in 1883, 82 in 2008, and 68 in 1900,

Key West  86  79  87  78 / 30 20 20 20
Marathon  89  78  89  79 / 30 20 20 20




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