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Area Forecast Discussion (AFD)

Issued by Key West, FL (KEY)

FXUS62 KKEY 200737

Area Forecast Discussion
National Weather Service Key West FL
337 AM EDT Sun May 20 2018

A large area of rain/showers/and a few thunderstorms extends from
the Gulf waters well offshore from Mainland Monroe county to the
Atlantic waters and Straits southeast of the Middle and Upper
Keys. More isolated showers and thunderstorms are in the waters
west of there. A weak trough is stretched just to the northwest of
the island chain. Under cloudy skies with a freshening
southeasterly breeze, temperatures along the island chain are in
the mid 70s. 

The weak surface trough will continue to move slowly to the
northwest through late today and tonight, and linger in the
eastern Gulf of Mexico into early Monday. A ridge of high surface
pressure will settle further south across the southeastern portion
of the U.S. and northern Florida through the middle of the week.
There will be little change in airmass and the wind profile
locally through that time as a resilient mid/upper trough hardly 
moves from the east central portion of the Gulf. With plenty of 
moisture in place, and persistent conditional instability, there 
is a well-above average probability of measurable precipitation 
for the Florida Keys today into at least the middle of the week. 
Beyond then, there is at least a possibility of low pressure 
stretching across the local area later this week and into next 
weekend. However, long range models continue to disagree among 
themselves with this potential low pressure area, and most are 
having run-to-run consistency problems. A low confidence forecast
remains through the later periods of the coming forecast. 
However, it remains a good bet to keep rain chances well above 
the norm for this time of year. There were no big changes to the 
gridded weather elements on this cycle. 


There is decent agreement that winds will freshen from the
southeast today. Felt confident enough to raise a small craft
advisory for the Straits of Florida today. Winds will be
occasionally fresh through the bulk of the week with a combination
of cautionary and advisory headlines for mainly offshore waters
through at least the first half of the work week.
Rain/shower/tstms coverage is also a concern through that time if
you have boating plans. 


Today, periodic mvfr cigs and/vis will be likely in scattered to 
numerous showers and isolated thunderstorms. Best chance for short 
period ifr cigs and/or vis will be this afternoon or after 18Z, so 
have a PROB30 in for those lower conditions. Surface winds will 
average between 12 and 15 knots from between 120-140 degrees with 
gusts between 20 and 25 knots. Pilots should prepare for temporary 
MVFR CIGS/VIS in any shower activity accompanied by wind gusts 
over 25 knots. 


On May twentieth 1932, 3.83 inches of rain was measured in Key
West. This set the daily rainfall record for the date in the city.
Rainfall records for Key West date back to 1871.


Key West  83  75  84  76 / 80 70 70 60 
Marathon  82  76  84  76 / 80 70 70 60 


GM...Small Craft Advisory GMZ052>055-072>075.



Data Collection......DAF

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