Area Forecast Discussion
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FXUS62 KKEY 202101

Area Forecast Discussion
National Weather Service Key West FL
401 PM EST Mon Feb 20 2017

.DISCUSSION...In the middle and upper levels, (700-200 mb), latest
available satelitte imagery overlaid with available model streamline
analysis as of 300 pm depicts the main north to south oriented
axis of a narrow yet very deep sharpening full latitudinal trough
which presently extends from North Dakota south to Central
Mexico. Hence, downstream of that feature, not surprisingly, is
an unseasonably deep middle and upper anticyclone with the main
ridge axis extending from Honduras to Central Ontario.

At the surface and in the lower to middle levels, (surface to 700
mb), latest available marine and land surface observations and
analysis as of 300 pm details a cold front situated from Southern
Manitoba to the Texas Panhandle. East of that, broad high pressure
exists over the Southeastern United States with stronger high
pressure over the northeast. Most importantly, there is now a near
1010 mb weak low pressure area over the Southwest Gulf of Mexico.

.CURRENTLY...As of 300 pm. skies are mostly clear across the
islands and surrounding waters. Temperatures thus far have reached
the Keys island chain with dewpoints backing off into the 60s.
C-man stations along the Florida Reef are recording mainly east
winds at 10 to 15 knots and gusty and 10 to 15 mph over the
islands. KBYX radar, now back in business attm, is recording a
few speckles of showers in the Florida Straits.

.SHORT TERM...Tonight thru Thursday Night, A period of foul
weather, winter time cloudiness and rain, seems to be more likely
be in the cards for late Tuesday night thru at least Thursday.
After another quiet night tonight and day Tuesday, will begin to
see clouds coming in Tuesday night. This will be in response to
the migration eastward of the aforementioned unusually deep and
narrow full latitudinal trough approaching the Gulf of Mexico to
the west. As the axis of this trough moves across the Gulf of
Mexico, it will induce surface low pressure ahead of the
associated surface frontal boundary. GFS has been inconsistent
with surface reflection for several runs prior to the last couple,
and now in both the 06 and 12 Zulu runs it brings back 1005-1007
mb surface lows developing Tuesday night and Wednesday, ranging in
location`s from NE Gulf to near the Keys, but now shows a
slightly deeper 1003 mb low near Grand Bahama Island late
Wednesday Night, THEN consolidating to a 1000 mb low north of Lake
Ocheochobee Thursday. The ECMWF has been consistently showing
developing 1002-1003 mb low pressure in the Eastern Gulf during
Wednesday, with a dumbbell of 1002 mb lows either side of the
Peninsula near Miami and west of Fort Meyers at 12Z Thursday. BUT
but both models et other have shows a near 560 decameters low at
500 mb moving SE across the Keys and South Florida Wednesday Night
and Thursday.

Given all that, showers are likely across the area for late
Tuesday Night through Thursday. Forecast soundings are showing
decent low to middle level speed and directional shear for morning
thru evening periods Wednesday. Given moderate PWAT between 1.5
and 2.00 inches, will include scattered thunderstorms in the
forecast. SPC has the Keys under a thunderstorms outlook for the
two periods as well. Will need to look more closely at QPF
categories in later forecasts as some showers and storms will be
capable of producing heavy rainfall. The surface low is progged to
finally be north of the Keys and pulling away during Thursday,
with only some light showers as mid levels warm by Thursday
afternoon and evening. High and low temperatures will be held back
into the middle to upper 70s Wednesday and Thursday, with lows in
the upper 60s.


.LONG TERM...Friday thru Monday, middle and upper level zonal flow
will return with no indications of any surface fronts. Surface
ridging is indicated to set up across the Florida Peninsula with
only light to gentle winds. Temperatures will be slightly above
normal, with a slight chance of showers, 10% in each period,
given forecast soundings depiction of low level moisture. The
weather will continue to be predictably fine!


.MARINE...Gentle to moderate winds expected to continue tonight
thru Tuesday Night, with moderate to fresh winds across the
Florida Straits. Then numerous showers and scattered thunderstorms
will impact the waters Wednesday and Wednesday night, becoming
scattered showers by Thursday. Given the uncertainty and the
dynamics associated with the depictions of surface low pressure
centers, there will be the distinct possibility that some heavier
showers and scattered storms could produce strong wind gusts thru
this time. As such have indicated that wording for the Tuesday
Night thru Wednesday Night Periods. Winds and seas will let down
by Thursday afternoon and onward. Outside of that, have
introduced SCEC conditions for Hawk channel maintained SCEC for
the Florida Straits for these periods. There is a high degree of
uncertainty for the middle portion of the week as far as these
wind speeds and direction are concerned, thanks to the scenario
described above. Thereafter, winds and seas will let down.


VFR conditions will prevail at EYW and MTH this afternoon through at
least Tuesday morning. Sustained northeast to east winds near 15
knots expected from just off the surface to about 3,000 feet.


On this date in Florida Keys weather history, in 1984, the high
temperature at Key West International Airport was 85 degrees. This
set the daily record for maximum temperature measured in Key West on
February 20th, a record which still stands 33 years later.
Temperature records at Key West date back to 1872.


Key West  72  83  69  76 / -  -  30 70
Marathon  72  84  70  77 / -  -  30 70




Upper Air/Data Collection......Chesser

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