Area Forecast Discussion
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FXUS62 KKEY 250903

Area Forecast Discussion
National Weather Service Key West FL
503 AM EDT Tue Apr 25 2017

A weak cold front passed through the Florida Keys yesterday late
afternoon and evening, followed by a short-lived period of fresh
west to northwest breezes. However, within the last few hours,
wind speeds have dropped, and currently, are averaging 10-15 knots
over water, and 10-15 mph over land. Latest Doppler radar scans
are void of precipitation echoes over the Florida Keys or
adjoining coastal waters, while geostationary satellite images
from the short-wave infrared channel show few to scattered shallow
stratocumulus clouds moving from west to east along and north of
the Keys, within the far southern cyclonic envelope of a
northeastward-moving, deep, midlatitude cyclone. Incoming air
trajectories are rooted in highly modified continental polar air,
having traveled several hundred miles of the Gulf of Mexico.
Therefore, the air mass change since yesterday is only modest to
say the least. Current air temperatures in most Keys island
communities are in the lower 70s, with dewpoint temperatures in
the mid 60s.

For today, any discernible low-level cold thermal advection will
cease by afternoon, and air temperatures will easily reach near
80F in most communities, under generally sunny skies. Gentle to
moderate west breezes will prevail, with an afternoon surge
developing mainly from Key largo to Ocean Reef.

Tonight, a developing low-level ridge will move northward across
the service area, with initially gentle moderate west breezes
turning north or light and variable by midnight. The light winds
and mostly clear skies will result in radiative cooling, and we
should see air temperatures dropping to the upper 60s in many
areas. The next 24 hours will, by far, be the most "comfortable"
for humans.

Wednesday, weak low-level warm thermal advection will commence as
a ridge moves farther northward and low-level winds attain a
southerly component. By Wednesday night, true maritime tropical
air will be arriving at the surface. However, a deep layer of dry,
stably stratified air will limit any shower production.

Thursday-Monday, a robust surface anticyclone will expand and
intensify over the western North Atlantic, beneath amplifying
ridging aloft. This will lead to freshening east-southeast breezes
and developing isolated shower coverage across the service area.
In addition, immersion in maritime tropical air will result in
high temperatures in the mid 80s, with low temperatures only
dropping to the upper 70s.

Gentle to moderate west breezes will prevail today most areas at
most times. However, winds are likely to surge in a small area
between the Everglades and the Straits of Florida off the upper
Keys late this afternoon, as mainland heating and associated
lowering of pressure induces a localized steeper pressure gradient
between about Flamingo and Bimini. Effects will be most
noticeable over eastern Florida Bay and from Molasses Reef
northward. Breezes should drop off rapidly after sunset.
Nevertheless, Small Craft Should Exercise Caution in these areas
late this afternoon. Thereafter, an area of high pressure will
build gradually over the Florida Peninsula from tonight through
Saturday. East-southeast breezes will freshen on Friday, with
Small Craft Advisories possibly required in some zones between
Friday night and Sunday night. At this point, we expect only
isolated showers Thursday and beyond with nil chance of

VFR conditions will prevail most of today with the exception of
brief MVFR ceilings at both EYW and MTH. Winds from the northwest at
5-10 knots will continue today with occasional gusts to near 15

The average high and low temperatures for April 25 at Key West,
based on the 30-year (1981-2010) historical mean are 82F and 73F.
The record high temperature is 90F, set in 1991, and the record
low temperature is 64F, set in 2012. The record daily rainfall
total is 2.21 inches, recorded in 1948.

Key West  81  69  83  76 / -  -  -  -
Marathon  81  69  85  76 / -  -  -  -




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