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Area Forecast Discussion (AFD)

Issued by Key West, FL (KEY)

FXUS62 KKEY 200736

Area Forecast Discussion
National Weather Service Key West FL
336 AM EDT Sat Oct 20 2018

.DISCUSSION...In the middle and upper levels( 700-200 mb), latest
available GOES-R satellite imagery overlaid with model streamline
analysis as of 300 am, depicts the near 595 decameter center of 
an expansive warm core middle and upper level anticyclone situated
over Lake Ocheochobee. The associated attendant western ridging 
is oriented northwest to southeast across the breadth of the Gulf 
to anticyclones center, with attendant eastern ridging stretching 
from the anticyclones center southeast to north of Hispaniola. To
the north of this feature exits a developing robust cold gyre 
over the Midwest and Northeast United States. As a result, upper 
confluent flow with 100-125 knotters westerlies at 250 mb are 
moving from the Central Plains east to off of the New Jersey 

At the surface and in the lower to mid levels(Surface to 700 mb),
latest available GOES-R satellite imagery overlaid with marine 
and land surface observations and surface analysis, depict 1025 mb
ridging extending from Northeast Texas east to off of the
Carolinas into the Western Atlantic near 35N 65W. A stationary
front is over South GA/AL/MS. As a result, last evenings 00Z
sounding at Key West illustrated a mostly east moderate to fresh
flow off of the surface up to 700 mb, which was also dry in the
lower to mid troposphere with PWAT only at 1.04 inches. Winds had
lightened up near the surface.

.CURRENTLY...As of 300 am, skies are mostly clear across the
islands and surrounding waters, with only one weak sole shower
identified in the Florida Straits. Temperatures across the islands
were near 80 degrees with dewpoints in the lower 70s. C-man
stations along the Florida Reef were northeast to east at 10 to 15
knots and at Smith Shoal. Winds over the island platforms were
closer to 10 mph. 

.SHORT TERM...Today thru Tuesday, 500 mb heights in association
with aforementioned middle level ridging will remain near 590 dm.
This will occur though a trough will impact the Northeast and
Middle Atlantic States Sunday thru Tuesday. After dry weather
today through Sunday, expect increasing breeze again by Sunday
Night as surface high pressure over the Mid-Mississippi Valley
moves quickly to the Carolinas and offshore Monday Night and
offshore Tuesday. As the ridging flexes it muscles it will push
surface/low level cool front back down the Peninsula Sunday and
Sunday Night. Although both 00Z ECMWF and GFS agree the surface 
front will not get this far south at this time, breezes and 
increasing convergence ahead of the front will result in low to 
mid chance for the development of showers and a few thunderstorms.
Specifically low chance beginning late Sunday night, as winds 
freshen from the northeast, middle of the road chances for Monday 
and Monday Night, 40%, with low chances for Tuesday, 30%. This is
above normal as we enter the end part of the wet season per

High temperatures Monday and Tuesday will be a few degrees lower 
given threat for showers and cloud cover, expected to reach the 
lower to mid 80s. Otherwise high humidity will still exist 
outside of showers despite breezy conditions over the islands late
Sunday Night and Monday, with winds coming down Monday night and 


.LONG TERM...Tuesday night thru Friday, surface ridging across the
Florida Peninsula will be not to far from the Keys. This combined
with elevated lower level moisture despite only gentle winds, will
allow for isolated showers and a few storms, (20% each 12 hour
period which is just near or above climo at this time in October)
thru the period. High and low temperatures will be near or 
slightly above normal with high humidity. Mid to upper 80s and mid
to upper 70s respectively. Indications of a possible FROPA, 
although still 6 or more days away, are starting to become more 
consistent in both the Ecmwf and GFS models, as they point towards
early next weekend.


.MARINE...Good boating conditions expected today thru Sunday,
then winds and seas increase from the northeast late Sunday 
night, with SCEC conditions across moist waters, and SCA 
conditions looking likely before sunup Monday across 
GMZ033-034-042>044-052>055-072>075 with SCEC conditions elsewhere.
SCA looks likely across all waters during Monday, with SCA 
conditions across the Florida Straits Monday night and SCEC 
conditions elsewhere. Winds and Seas let down again during Tuesday
thru much of next week. 


until 00z/20th, VFR conditions will prevail at the Key West and 
Marathon terminals. Northeast to east winds of less than 10 knots 
will turn east to southeast near 10 with occasional gusts of 15 


In 1940, the daily record low temperature of 65 degrees was recorded
in Key West. Temperature records date back to 1872. 


Key West  88  78  87  78 / -  10 10 30 
Marathon  88  77  87  78 / -  10 10 30 





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