Area Forecast Discussion
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FXUS62 KKEY 200848

Area Forecast Discussion
National Weather Service Key West FL
448 AM EDT Fri Oct 20 2017

Scattered small showers were detected by the local Doppler radar
early this morning across the Florida Keys coastal waters. As
observed from satellite imagery, these were being brought in with
the northeast wind flow, creating a shadow over the gulf side
waters, where showers coverage was isolated. Minimum temperatures
were only able to drop to the near 80 degrees across the Keys with
winds from the east northeast at near 10 mph.

A high pressure over the southeast US this morning, will stretch
into the Florida peninsula and the Florida Keys. This will cause the
pressure gradient to tighten with a wind flow from the northeast
to east. The high will shift to the east later tonight, veering
the winds locally from the east. PWAT values will be near one inch
and three quarters today and with the wind flow from the
northeast to east, the eastern waters of our local forecast area
will be the ones getting most of the showers this morning,
reaching the gulf side waters by this afternoon. By Saturday
morning, the high is expected to get into the Atlantic waters and
it will continue to lift to the northeast. Winds locally will be
from the southeast by Sunday. More details about the winds
forecast for today is below in the Marine section.

By Sunday, a low pressure is despited by both GFS and Euro models
developing near Louisiana and by Monday night being over northern
Alabama (faster in the Euro). A cold front will stretch from it
and move over the eastern Gulf of Mexico on Tuesday. By Tuesday
night, the front will stretch from the northeast US across
central-south Florida. Again, the GFS brings the front faster
through the Florida Keys than the Euro. Went with the GFS but this
will be adjusted during the next few days. Regardless of when
this front moves over the Keys, great news: lower dew points are
expected to finally reach us! Fall weather will make its appearance
just in time for the local festivities.


Operators of small craft should exercise caution today due to northeast
to east winds. The GFS is a bit higher with winds for this evening
and tonight, while the Euro keeps the winds below advisory for the
most part. A blend of these was used but it will be reexamined
with the new guidance and an advisory may be required for tonight
and possibly extending through most of the weekend. By Monday,
winds should drop below advisory until the passage of a cold front
on Wednesday.


High pressure centered over the central Appalachian mountains will
strengthen today, increasing the pressure gradient across the
Florida Peninsula and the Keys. As a result, the island terminals
will see increasing east-northeast breezes, starting the day at
10 knots or less, increasing to between 12 to 15 knots with gusts
of 20 to 23 knots by this afternoon. VFR conditions are expected
to prevail as any quick moving showers that clip the terminals
will yield only brief and minimal operational impacts.


On this date, back in the year 1940, the low temperature of 65F was
observed, setting the daily record low temperature for October 20th
in Key West. It has been 164 days since the mercury dipped below 70F
in Key West, when a low temperature of 69F was observed on May 9th.
Temperature records in Key West date back to 1872.


Key West  86  77  85  78 / 40 30 30 40
Marathon  86  77  86  78 / 40 30 30 40





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