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Area Forecast Discussion (AFD)

Issued by Key West, FL (KEY)

FXUS62 KKEY 151606

Area Forecast Discussion
National Weather Service Key West FL
1106 AM EST Thu Nov 15 2018

.DISCUSSION...In the middle and upper levels( 700-200 mb), latest
available GOES-R satellite imagery overlaid with model streamline
analysis as of 1000 am depicts a developing powerful middle and
upper cyclone over Illinois, with an attendant NNE-SSW cold 
trough axis that extends unusually far south and terminates in 
the Pacific west of Southern Mexico. Conversely, and downstream of
that, the aforementioned low pressure is assaulting the northwest
to southeast oriented ridge positioned from Western New England 
SSE to well east of the Carolina, and there is a TUTT like feature
south of that is becoming more disheveled as it slows down east o
the Northern Bahamas. 

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, as of 1000 
am, detail low pressure near Charleston SC dragging a cold front
that is now bisecting the Keys thence southward to near the
Honduran Coast. As such the 12Z sounding at Key West near the time
of FROPA. still illustrated an exceptionally moist moderate to
freshening south to southwest flow from off the surface up to 500
mb. Above that within deep cyclonic flow, winds veer to more 
southwest up to 200 mb.

.CURRENTLY...As of 1000 am, skies are partly to mostly cloudy
across the Keys island chain and surrounding waters, as the front
is more or less bleeding across the islands from west to east.
Radar detects widely scattered showers confined to the Eastern
half of the CWA, with isolated activity across the Western half of
the CWA including the Dry Tortugas. Attm, there are mostly sunny
passage across the Western Florida Straits as well as the Offshore
Gulf waters and in the Southeastern Gulf of Mexico waters out to
the Tortugas. The surface cold front is moving a little more 
quickly than expected from west to east. Observations suggest SCA 
conditions have arrived across the waters north, west and south of
the Lower Florida Keys, with breezy conditions developing across 
the Lower Florida Keys. Across the Middle and Upper Florida Keys, 
Northwest winds are averaging 10 to 15 knots except around the 

.SHORT TERM...Rest of today and this evening, expect windy
conditions to develop across the rest of the islands by late this
afternoon across the waters with breezy to windy conditions over
the islands. The strongest winds, 20 to 25 mph will be across the
Lower Keys, with winds between 15 and 20 mph reaching 20 mph by
later in the afternoon across the rest of the Keys. The other
issue is that as 1000-925 mb cold thickness advection begins in
earnest thru the afternoon, should see in situ development so
stratus and strato-fractus upstream of the Keys, reintroducing
mostly cloudy skies across the islands. Forecast soundings 
continue to ample lower to middle level moisture remaining in
place post-frontally. As such, this will allow development of
widely scattered light rain or showers by afternoon, which may 
deliver several hundreths of an inch at best. Have trimmed pops 
back to 30 percent, or low chance for rain at any given spot along
the island chain. Cloudy and windy weather will continue this 
evening with just isolated sprinkles or light rain showers around.
No other changes on this update cycle. 


.MARINE...SCA conditions already occurring at GMZ033-035, GMZ044,
GMZ054-055 & GMZ074-075. East of those marine zones, SCA 
conditions will develop by 22Z across the rest of the marine 
district. SCA conditions expected across all waters tonight and at
least the first half of Friday. By Friday afternoon, the 
shallower waters will have cooled sufficiently, so for GMZ031-032 
and maybe GMZ035, winds and seas should down during the 
afternoon, possibly below SCEC. Another brief surge is possible 
Friday Night, with SCEC headlines likely across all waters. SCEC 
conditions are possible across portions of the waters Saturday 
morning, but winds and seas a forecast to let down appreciably 
thereafter, with moderate breezes still expected. BUT, confidence 
is low as a another reinforcing high could hike the winds into 
headline territory once again through early next week


Pre-frontal showers have moved out of the Keys. Expect mainly VFR 
conditions this afternoon, with periods of MVFR ceilings. These MVFR 
ceilings move into the Keys again after 16/00Z associated with the 
relatively cooler air moving over the still warm Gulf waters. Strong 
north winds behind the cold front will drive crosswind values near 
20 knots today and tonight as wind directions will be normal to the 
runways. Winds at FL010 will be 20 to 25 knots through the end of 
the forecast period. 


.CLIMATE...On this date in 1916, a tropical storm that developed 
in the central Caribbean Sea acquired extratropical 
characteristics over the SE Gulf of Mexico and moved rapidly 
northeast along the entire length of the Keys. Sand Key recorded 
maximum sustained winds of 71 mph, while Key West reported maximum
sustained winds of 52 mph with a minimum pressure reading of 


GM...Small Craft Advisory all waters by this afternoon



Upper Air/Data Collection......BT

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