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Area Forecast Discussion (AFD)

Issued by Key West, FL (KEY)

                            
427 
FXUS62 KKEY 201958
AFDKEY

Area Forecast Discussion
National Weather Service Key West FL
258 PM EST Sat Jan 20 2018

.DISCUSSION...
Air temperatures have been slow to increase today thanks to
persistent cloud cover and northeast breezes off cool Gulf and Bay
waters. Even now, air temperatures in most Keys island communities
remain in the upper 60s, with dewpoint temperatures near 60F.
Gentle to moderate, mostly northeast breezes prevail, with a
combination of cirrus, altocumulus, and stratocumulus cloud
varieties overhead. Key West Doppler radar scans remain void of
precipitation echoes. The atmosphere is just too stable and dry at
this point. This may change tonight, mainly late, and mainly over
the Straits of Florida where the warmer water will support some
shallow convection. Air temperatures should easily fall into the
mid 60s this evening, even while dewpoint temperatures inch upward
overnight. 

Prognostic reasoning is consistent with the previous forecast
cycle, and most adjustments to digital and derived forecasts are
minor. The primary storm tracks (and associated forcing for
large-scale ascent) will remain far north of the service area.
Therefore, local wind and weather will be modulated primarily by
the positions, shapes, and intensities of the governing 
anticyclones. Through Tuesday, a modified continental polar
anticyclone will shift very slowly eastward over the western North
Atlantic. A decent gradient will exist between the Straits of
Florida and northern marine zones, with the ridge north of the
service area. This gradient will be enhanced by significant
north-south variations in sea surface temperatures and associated
lower temperatures/higher pressures in the lower atmosphere. 

By Wednesday, a robust continental anticyclone will be expanding
and intensifying across the southern United States, moving toward
the Keys and adjacent coastal waters, with a significant
northeast to east wind surge looking increasingly likely for the
end of the week.
&&

.MARINE...
Small Craft Advisory conditions are expected in the Straits of
Florida tonight. Wind speeds should decrease abruptly between the
much warmer waters of the Gulf Stream and the cooler waters just
inside the Florida Reef tract. An area of high pressure will 
extend from the southeastern United States to the western North 
Atlantic Ocean, from tonight through Sunday. This system will 
weaken and shift eastward Monday and Tuesday. Another continental 
high pressure system will expand and intensify across the 
southeastern United States Wednesday and Thursday. 
&&

.AVIATION...
Through 21/18Z, prevailing VFR conditions are expected at both EYW
and MTH.
&&

.CLIMATE...
On this date in 1983, 2.84 inches of rain fell in Key West,
setting the daily rainfall record for January 20. An additional
13.36 inches fell during the following three days, making January
20-23, 1983 one of the wettest four-day periods at Key West since
official rainfall records began in 1871! 
&&

.PRELIMINARY POINT TEMPS/POPS...
Key West  65  74  66  77 / -  10 20 20 
Marathon  65  74  66  77 / -  10 20 20 
&&

.KEY WATCHES/WARNINGS/ADVISORIES...
FL...None.
GM...None.
&&

$$

Public/Marine/Fire...Kasper
Aviation/Nowcasts....Kasper
Data Collection......Chesser

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