Area Forecast Discussion
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FXUS62 KKEY 230853

Area Forecast Discussion
National Weather Service Key West FL
453 AM EDT Wed Aug 23 2017

An upper-level composite analysis this morning reveals a weakening
deep layer mean anticyclone over the western North Atlantic, with
a broad trough/cyclonic vorticity zone now covering most of South
Florida, the Straits of Florida, Cuba, and the northwestern
Bahamas. An area of rich tropical moisture advected into the
service area during the last 24 hours, and numerous, slow-moving
showers and thunderstorms have developed, with some associated
long-lived residual stratiform rain areas as well. Winds are quite
weak below 300mb, generally less than 15 knots, with much stronger
northwest winds above. Currently, both air and dewpoint
temperatures in most Keys island communities are in the upper 70s
to near 80F, making it nearly saturated at the surface, with
relative humidities of 90-100 percent.

Weak cyclonic flow in the lower and middle troposphere combined
with a very moist, unstable, and weakly inhibited atmosphere
should yield above-average rain chances from today through Friday.
Thereafter, a weak Atlantic low-level ridge should begin building
slowly, and gradually, across the northern Bahamas, and then
South Florida. Some locally heavy rainfall amounts will be
possible during the next few days due to rich tropical moisture in
the boundary layer, healthy rainfall rates associated with warm
rain processes, slow-moving cells, and some upscale growth
potential. &&

No watches, warnings, or headlines. Mostly variable breezes are
expected today and tonight. A weak trough will linger near South
Florida from today through Sunday. Winds and seas will be higher
in and near scattered to numerous showers and thunderstorms.

VFR conditions will prevail at both EYW and MTH. Slow-moving
showers and thunderstorms will develop along bands and if showers
and storms threaten to impact either/both terminals, an amendment
will likely be issued for MVFR/IFR cigs and/or vis. Short periods
of visibility down to less than 3SM, and isolated wind gusts to
25 knots are possible in the heavier showers, with the duration
generally less than an hour at a time. Winds will be variable at 6
knots or less outside of any showers and thunderstorms.

Daily record Key West rainfall for 23 August is 2.11 inches,
recorded in 1889.

Key West  89  80  89  81 / 60 60 60 50
Marathon  93  79  93  81 / 60 60 60 50




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