Friday, December 18, 2009

WATCHES: Tornado Watch Number 804

WWUS20 KWNS 181221
SEL4
SPC WW 181221
FLZ000-CWZ000-181800-

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 804
NWS STORM PREDICTION CENTER NORMAN OK
820 AM EDT FRI DEC 18 2009

THE NWS STORM PREDICTION CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF

SOUTH FLORIDA AND THE FLORIDA KEYS
COASTAL WATERS

EFFECTIVE THIS FRIDAY MORNING AND AFTERNOON FROM 820 AM UNTIL 200
PM EDT.

TORNADOES...HAIL TO 0.5 INCH IN DIAMETER...THUNDERSTORM WIND
GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE
AREAS.

THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 80 STATUTE
MILES NORTH AND SOUTH OF A LINE FROM 40 MILES SOUTH OF NAPLES
FLORIDA TO 20 MILES SOUTHEAST OF WEST PALM BEACH FLORIDA. FOR A
COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE
UPDATE (WOUS64 KWNS WOU4).

REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR
TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS.

DISCUSSION...A BROKEN BAND OF THUNDERSTORMS...SOME OF WHICH ARE
SUPERCELLS...WILL CONTINUE TO SPREAD NWD/NEWD ACROSS S FL AS A
SURFACE LOW DEEPENS ACROSS THE NE GULF OF MEXICO. A GRADUAL
INCREASE IN LOW-MID LEVEL WIND SPEEDS AND VERTICAL SHEAR...ALONG
WITH LOW-LEVEL MOISTENING AND SOME SURFACE HEATING IN SMALL CLOUD
BREAKS...WILL CONTRIBUTE TO AN INCREASING THREAT FOR SUPERCELLS AND
A COUPLE OF TORNADOES THROUGH THE MORNING.

AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 0.5 INCH. EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
500. MEAN STORM MOTION VECTOR 22020.


...THOMPSON

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