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Area Forecast Discussion (AFD)

Issued by Key West, FL (KEY)

FXUS62 KKEY 210754

Area Forecast Discussion
National Weather Service Key West FL
354 AM EDT Sun Oct 21 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 two near 595 decameter centers of 
regional warm core middle and upper level anticyclones situated at
the Northern Bahamas at 24N 75W, and another in the Western Gulf
of Mexico at 23N 96W. To the north of these features exists an
approx 75 to 125 knot average jet at 250 mb pushing from near
Kansas City east southeast, rounding the base of a trough over
North Carolina out to sea. 

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 a
building 1030 mb cold surface high centered near Omaha. A cold
front exists well southeast of that, from well east of New England
southwest to across South Georgia and west along the Northern Gulf
coast. As a result, last evenings 00Z sounding illustrated a 
gentle southeast flow backing to northeast between 850 and 700 mb,
but the column was very dry with PWAT only at .78 inches. 

.CURRENTLY...As of 300 am, skies across the islands were mostly
clear. Temperatures have radiated over the larger islands, down to
the lower 70s over Big Pine Key, but generally middle to upper 70s
elsewhere over land, with dewpoints in the lower to mid 70s. C-man
stations along the Florida Reef are recording variable winds near
5 knots, except north at 5 to 10 knots at Smith Shoal Light, with
island platforms generally variable at 5 mph or less. 

.SHORT TERM...Today thru Tuesday, the center of the 500 mb ridging
will slide slowly southwards as troughing along the Northeast and
Mid-Atlantic builds a bit southwards by early next week. A the
surface, weak ridging nearby today will be pushed away as a much 
stronger 1030 mb plus anticyclone centered over the Mid-
Mississippi Valley this morning moves to the Outer Banks late
Monday afternoon and slowly eastward Monday Night. As a result of
this stronger high gradually bridging, variable winds this 
morning, will become light to gentle by the end of today. Then
tonight breezy northeast winds bleed down into the marine
district, with breezy to windy conditions expected for Monday and
breezy conditions Monday Night. Given the fresh somewhat cooler breezes
across the warm waters, near surface convergence will result in
development of widely scattered showers and isolated thunderstorms
late tonight, especially Monday and Monday Night. As the surface
high pulls farther into the Western Atlantic on Tuesday, winds and
seas will come down. Hence will continue to advertise low to 
medium chances for showers with isolated storms thru this entire 
period(30-40%). The breezy conditions and slightly lower 
temperatures only reaching the middle 80s and lows in the mid to 
upper 70s, will make is more tolerable despite continued high 


.LONG TERM...Tuesday Night thru Saturday, a weaker pressure 
pattern will return for what may likely be the last week of pre 
cold-frontal weather very late in this wet season. Gentle to 
moderate breezes Tuesday will become light to gentle mostly east 
through Friday. High in the mid 80s and lows in the upper 70s are
expected thru the period. Then both ECMWF and GFS are indicating
that energy dives out of Canada re-carving out the longwave 
pattern associated with the Eastern trough. As this occurs, both 
GFS and ECMWF are starting to show development of a mid 
latitudinal cyclone somewhere from the NE Gulf to east of North 
Carolina during Saturday. This will result in clocking light to 
gentle winds Friday, freshening in advance of a cold front which 
could move across the area Saturday, per latest ECMWF. Some 
forcing and weak dynamics would mean that a broken line of showers
and storms could move across the Keys to mark a possible FROPA. 
Given that this is like 6 day out, will just tick pops up 10% for 
now with veering winds indicated in the grids.


.MARINE...Last day for good to great boating conditions, the SCA
conditions develop late tonight across
GMZ033-034-042>044-052>055-072>075 before sunup, with SCA
conditions expected during Monday across
GMZ033-034-042>044-052>055-072>075 with SCEC across GMZ031,
GMZ032-035, and SCEC conditions all waters Monday Night. Winds and
seas let down during Tuesday and no headlines or advisories
anticipated for the rest of the week.


Until 00z/22nd, VFR conditions will prevail at the Key West and 
Marathon terminals with light north to northeast winds of less than 
10 knots.


In 1964, the daily record low temperature of 64 degrees was last 
recorded in Key West. Temperatures have been kept since 1872.


Key West  87  79  85  79 / -  30 40 40 
Marathon  87  79  85  79 / -  30 40 40 





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