Area Forecast Discussion
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FXUS62 KKEY 220919

Area Forecast Discussion
National Weather Service Key West FL
419 AM EST Wed Feb 22 2017

Winds are freshening from the south across the bulk of the Keys
service area early this morning. An area of low pressure is
currently positioned in the northeastern Gulf of Mexico, with a
weak cold front trailing to the south/southwest. Ahead of the
front is an elongated area of showers with a few embedded
thunderstorms, currently pushing eastward into our service area
with the strongest cells just west of the Dry Tortugas. Under
increasing cloud cover, temperatures in the Florida Keys are in
the lower to mid 70s.

No reason to deviate from the categorical probability of
measurable rain today. Light showers should be very near the
Lower Keys between 5 and 6 am, followed by moderate to heavier
showers between 7 and 8 am. Expect the coverage to increase
eastward across all portions of the Keys through the morning. The
vort max, clearly evident on satellite, is not catching up as
quickly to the leading activity as previously expected. Lighter
and moderate showers with lowered clouds will linger beyond the
initial heavier rains through the afternoon, so do not have the
confidence to taper the probability of measurable precipitation
later in the first period. However, guidance does agree that the
probability and coverage of showers does diminish tonight. So,
started the tonight period with an elevated probability of
showers, then taper it to a chance through the overnight period.
It would not be surprising if this needs to be trimmed further for
the early morning hours on Thursday. As the low pressure slowly
but steadily pushes northeastward later this week, high pressure
rebuilds across the state in conjunction with a low amplitude mid
to upper level ridge pushing eastward through the eastern Gulf.
There were no changes to the gridded weather elements from
Thursday night onward. Expect temperatures at or slightly above
the seasonal average through the duration of the forecast, and a
return of a slight chance of showers early next week as our flow
deepens from the east.


A small craft advisory has been raised for all marine zones
surrounding the Florida Keys. The latest available ASCAT images
show an increase in the southerly breezes, especially across our
western Gulf zones and the Straits. VWP has shown an increase in
lower level winds since that pass, and the available observation
platforms near and around the Lower Keys are already sensing winds
AOA 20 knots. Westerly breezes will diminish by a few knots
tonight, and remain gentle to moderate into this weekend while
clocking slowly to the northeast. Breezes will moderate/freshen
later in the weekend as high pressure strengthens to our north.


An upper low is trekking across the northern Gulf of Mexico this
morning, with an area of low level vorticity moving quickly to the
southeast on its heels. The vorticity will likely catch up to a
boundary  producing showers and thunderstorms as it arrives near the
Lower Keys and Key West International between 22/11z and 22/12z.
Expect a surge in winds out of the south, producing a moderate
crosswind concern in gusts to near 20 knots. The timing on winds
shifting from south to west will occur around 22/15z to 22/18z and
will provide better guidance at the 09z amendment. The trough will
pass quickly with winds shifting to west to northwest around 23/01z
this evening, while showers move to the northeast.


On February 22nd, 1966, 2.54 inches of rain fell on Key West and
set the daily record for rainfall. After 51 years, this record may
have a chance of falling this afternoon. Rainfall records for Key
West date back to 1871.


Key West  76  67  77  68 / 90 60 30 10
Marathon  79  67  77  68 / 90 60 30 10


GM...Small Craft Advisory GMZ031>035-042>044-052>055-072>075.



Data Collection......Chesser

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