Area Forecast Discussion
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FXUS62 KKEY 191407

Area Forecast Discussion
National Weather Service Key West FL
1007 AM EDT Thu Oct 19 2017

.DISCUSSION...In the middle and upper levels(700-200 mb), latest
available satelitte imagery overlaid with model streamline
analysis as of 900 am continues to depict a progressive autumnal
pattern across the CONUS with one axis trough aligned along the
East coast, now moving offshore and another upstream ridge aligned
over the Plains, but more importantly latest water vapor imagery
delineates much drier air surrounds the entire Florida Peninsula
with its southern boundary now over all of the Florida Keys.

At the surface and in the lower to middle levels, (Surface to 700
mb), latest available satelitte imagery overlaid with marine and
land surface observations and analysis as of 900 am detail the
surface ridge axis off a northeast to southwest oriented
anticyclone positioned across the NW Atlantic near 40N 65W
southwest to North Georgia. Well south of that, a NE-SW stationary
front is hanging just southeast and parallels to the Middle and
Upper Florida Keys. AS such, the 12Z sounding at Key West
illustrated a gentle northeast flow from the surface up to about
700 mb, then becoming westerly above that, but becoming strong
westerlies above 500 mb, and the lower to mid troposphere portion
of the column was still moist up to 500 mb, though PWAT declines
to 1.79 inches and is down around 4 tenths of an inch in 24 hours.

.CURRENTLY...As of 900 am, Key West and Miami radar detect widely
scattered showers and possibly a few storms exist over the
Florida Straits with no echoes over the Florida Keys and points
north attm. Skies are mostly sunny over the islands, but mostly
cloudy over the Florida Straits. Temperatures across the islands
are in the upper 70s with dewpoints in the lower 70s. C-man
stations are recording North to northeast winds at 10 to 15 knots,
and island platforms are generally northeast near 10 mph.

.SHORT TERM...Rest of the day and this evening, combination of the
hung up frontal boundary just SE of the Keys and the anticyclone
well north of the Keys will maintain a gentle to moderate
northeast flow across the Keys. The aforementioned middle and
upper level trough will continue to move away and flatten out.
Although forecast soundings continue to show more drying
throughout the afternoon and evening, enough moisture around below
about 850 mb and some convergence to support some isolated showers
moving across the islands, but any rainfall amounts will be
light. So we retain the 20% pops. Skies on balance will be mostly
sunny, mostly cloudy to the south over the Straits where the
frontal boundary continues to slowly wither and widely scattered
showers and evening a lightning strike is possible. Hence, no
changes to the ongoing forecast on this cycle.


.MARINE...Winds are slightly elevated for the aforementioned
reasons, so will start off with gentle to moderate across all
waters. Models are all underdone in the initialization. However,
surface ridging will regain control by late afternoon after the
boundary to the SE complete frontolysis this evening. Hence, winds
will ramp up this evening, with a SCA to be issued for at least
the Florida Straits for tonight, and at least an SCEC likely for
Hawk Channel, the extreme SE Gulf of Mexico waters, and the
offshore Gulf waters. This will be the focus for the afternoon
forecast package.


.AVIATION...VFR conditions will prevail at the island terminals.
Winds will be 5 to 10 knots generally from the northeast.




Upper Air/Data Collection......DR

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