Area Forecast Discussion
Issued by NWS
FXUS62 KKEY 301918
Area Forecast Discussion
National Weather Service Key West FL
318 PM EDT FRI SEP 30 2016
.DISCUSSION...In the middle and upper levels(700-200 mb), latest
available IR imagery overlaid as of 200 pm, overlaid with model
streamline analysis depict a deep middle and upper level trough
centered over the Middle Ohio Valley with an attendant axis extending
south into the NW Caribbean Sea. Well to the southwest of that, the
center of an east to west oriented expansive deep and warm core
middle and upper level ridge was located over Central Mexico, with
the eastern periphery of the ridge reaching near the Yucatan
At the surface and in the lower to middle levels, (Surface to 700
mb), the center of a near 1035 mb early autumnal high pressure
system was over Western Quebec, but well south of that an attendant
now stationary front extends from surface low pressure over the
North Carolina Mountains to Central Florida thence into the Central
Gulf at about 90 West. The western edge of a weak surface ridge
pokes into South Florida. Of course across the tropics, the center of
Hurricane Matthew, was located in the South Central Caribbean Sea,
near 13.6 North 71.3 West at 200 pm EDT. Maximum sustained winds are
near 120 mph and the storm continues to move to the WSW or 255
degrees at about 10 knots.
.CURRENTLY...As of 200 pm, skies are mostly sunny across the Keys
and all adjoining waters. Temperatures across the islands have risen
to near 90 degree with dewpoints in the upper 70s. Radar detects only
a few showers in the distant Eastern Florida Straits...moving
little. Visible satellite imagery combined with radar does indicate
the beginnings of a developing cloud line with a few showers from
near the 7 mile bridge to north of Sugarloaf Key. C-man stations
along the reef are registering East to southeast winds near 5 knots.
.SHORT TERM...Tonight through Tuesday, NHC forecast track for
Hurricane Matthew brings the system westward tonight, west
northwestward during Saturday, northwestward Saturday night and
Sunday, then northwards during Monday and Tuesday. Locally, the
surface frontal boundary will remain across Central Florida tonight.
Average moisture in the boundary layer and little storm motion
through late this afternoon and evening will allow for scattered
showers and isolated thunderstorms within a cumulus cloud line.
Surface ridging across the SE United States and movement of Hurricane
Matthew will allow gentle to moderate northeast to east breezes
across the islands and adjoining waters for Saturday through Sunday
Night. Available 12Z GFS and ECMWF model forecast soundings
illustrate PWAT will remain between 1.75 and 2.00 inches. Given
additional convergence, will maintain middle of the road chances for
showers and thunderstorms, which is slightly above average for this
time of year. Then for the Monday thru Tuesday periods, winds will
increase a bit with the closest approach of Hurricane Matthew across
the Northern Bahamas from the South.
Given that the Keys may be in the path of outer rainbands, will
continue to carry a high chance for pops for these periods, given
squalls with rainbands. If the system moves more to the East, then
present weather conditions may actually be much better, and rain
chances and sensible weather may be much better then advertised. It
is important to remind users that average NHC track forecast errors
are around 175 miles at day 4 and 230 miles at day 5. Therefore, it
is too soon to rule out additional possible hurricane impacts other
than some showers and squalls within outer rainbands from Matthew.
While there still remains some uncertainty on potential impacts of
Hurricane Matthew for the Florida Keys, now is the time to review
hurricane preparedness plans and to make sure your hurricane supplies
are fully stocked. Interests in the Florida Keys should continue to
remain well informed on the forecast regarding Hurricane Matthew with
the latest information from the National Hurricane Center and the
National Weather Service Office here in Key West.
.LONG TERM...Hurricane Matthew will continue to track northwards
during Wednesday and Thursday. Fresh to strong Northwest to North
breezes Tuesday Night and Wednesday should abate quickly by Wednesday
night. A typically weak early fall surface ridge of high pressure is
then slated to build just north of the Florida Keys thereafter, and
given moisture profile, climatological low chance pops are retained
in the grids for those periods.
.MARINE...Light to gentle winds are expected across the waters
tonight, with gentle to moderate winds for Saturday through Monday.
No headlines or advisories are expected across the waters through the
period, but a few waterspouts will be possible within cloudlines
developing near the Keys.
As Hurricane Matthew tracks closer to the region early next week,
hazardous marine conditions will be possible, with conditions
expected to deteriorate across eastern portions of the waters Monday
night through Wednesday. The highest winds...seas and swells would
occur across the Eastern Florida Straits given the present forecast,
and small craft advisory conditions appear likely during this time
for these waters. Of course special marine warnings will also likely be
issued for fast moving showers and storms within rainbands across
all of the waters.
Marine interests should continue to remain well informed on the
latest forecasts from the National Hurricane Center and the National
Weather Service Forecast Office in Key West.
.AVIATION...Brief mvfr/ifr conditions possible within showers and
isolated storms possible within cumulus.towering cumulus cloudlines
which may impact either/both KEYW and KMTH In`tl Island terminals
this evening. Isolated showers and storms possible overnight.
Amendments will be issued as required.
.PRELIMINARY POINT TEMPS/POPS...
Key West 79 86 80 87 / 30 40 40 40
Marathon 79 86 79 87 / 30 40 40 40
Visit us on the web at weather.gov/key
Follow us on Facebook and Twitter at: