Area Forecast Discussion
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FXUS62 KKEY 010224

Area Forecast Discussion
National Weather Service Key West FL
1024 PM EDT FRI SEP 30 2016

.DISCUSSION...An active evening of convection across the Florida
Keys. For the first time in several days, a deep layer (up to 700mb)
of moist easterlies was sampled by the KKEY RAOB. This rich and
confluent tap of moisture has provided ample fuel for multiple
rounds of showers and thunderstorms. Aiding vertical development, a
short wave in the south-central Gulf of Mexico is evident on water
vapor imagery rounding the base of a parked long wave trough. The
CIMSS vorticity analyses relegate this curvature to near 200 mb,
however, the coverage and cycling of convection this evening begs to
differ. MSLP analyses indicate a weak ridge axis washes out near
eastern Florida, with a weak pressure pattern across the Florida Keys
and the Southeastern Gulf of Mexico. Current loops from the KBYX
radar indicate erratic cell motion, aside from the southeastern
Straits of Florida where cells have a noticeable motion towards the
west- southwest.

.FORECAST...A review of current loops from MIMIC TPW and water vapor
imagery indicate the ingredients which were available earlier this
evening remain in place. The moderate instability sampled by the 00Z
RAOB has been overturned, and large areas of stratiform rain remain.
Given 10 to 15 knots of easterlies in the lower troposphere, and mid
latitude infusions above 500 mb, the atmosphere should destabilize
overnight. We inherited MOS statistical guidance ranging between 20
and 50 percent for the overnight period. An earlier update increased
rain chances to 50 percent which may have been too conservative.
Expect scattered to numerous showers and storms overnight, with lows
dipping into the upper 70s within rain cooled downdrafts. Mostly
cloudy skies will persist. No other changes planned for the digital
or derived forecasts.


.MARINE...No watches, warnings, or advisories are in effect, and the
forecasts contain no headlines. Northeast to east breezes will slowly
freshen across the coastal waters of the Florida Keys tonight
through Monday as Hurricane Matthew moves northward through the
Caribbean Sea towards eastern Cuba. Matthew will continue northward
through the Bahamas Tuesday through Wednesday. Strong northeast
breezes will shift to the north as Matthew moves through the
Bahamas. The strongest winds and largest seas will be confined to the
eastern- most portions of the Straits of Florida and Hawk Channel.
Please stay informed this weekend concerning the evolution of
Hurricane Matthew.


.AVIATION...Scattered showers and thunderstorms with tops
occasionally over FL400 in the vicinity of KMTH and KEYW this evening
may provide brief IFR visibilities...otherwise mostly VFR is expected
after 06Z into the morning hours Saturday. Winds have been a bit
chaotic this evening near thunderstorms with gusts up to near 25
knots...but are expected to settle out of the east northeast this
evening with speeds 10 knots or less through Saturday morning.


.TROPICAL...The latest information on Hurricane Matthew is included
below. It is important to remember 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 possible hurricane impacts from
Matthew in Florida.

At 800 PM EDT, Hurricane Matthew was located near latitude 13.5
North, longitude 72.0 West. Matthew is moving south of due west near
9 mph. A westward motion at a slower forward speed is expected
tonight and Saturday. A turn toward the west- northwest is forecast
by Saturday night, followed by a turn toward the northwest on Sunday.
The center of Matthew will move across the central Caribbean Sea on
Saturday, and be near Jamaica late on Sunday.

Data from an Air Force Hurricane Hunter aircraft indicate that
maximum sustained winds have increased to near 150 mph. Matthew is a
category 4 hurricane on the Saffir- Simpson Hurricane Wind Scale.
Some fluctuations in intensity are possible this weekend, but Matthew
is expected to remain a powerful hurricane through Sunday.

The latest minimum central pressure just reported by an Air Force
reconnaissance aircraft was 945 mb (27.90 inches).


.KEY Watches/Warnings/Advisories...


Data Collection......Vickery

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