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TROPICAL STORM DEAN DISCUSSION NUMBER   3
NATIONAL WEATHER SERVICE MIAMI FL
11 PM EDT WED AUG 22 2001

WITHOUT RECON OR VISIBLE SATELLITE IMAGERY...THE LOCATION IS ALMOST 
IMPOSSIBLE TO PINPOINT.  RADAR FROM SAN JUAN IS INCONCLUSIVE...AND A 
RECENT QUIKSCAT PASS SHOWS DEAN AS AN OPEN WAVE.  THE INITIAL 
POSITION...MOTION...AND SHORT-TERM FORECAST ARE BASED ALMOST 
EXCLUSIVELY ON CONTINUITY FROM LAST-LIGHT SATELLITE TRENDS.
 
THE INTENSITY FORECAST IS PARTICULARLY CHALLENGING TONIGHT.  DEAN IS
CURRENTLY EXPERIENCING FAIRLY STRONG WESTERLY SHEAR...AS A RESULT OF
A SHARP UPPER TROUGH OVER THE SYSTEM COUPLED WITH STRONG LOW-LEVEL
EASTERLIES...AND MAY IN FACT NO LONGER HAVE A CLOSED CIRCULATION.
HOWEVER...OVER THE NEXT 24 HOURS DEAN SHOULD BE MOVING UNDER AN
UPPER ANTICYCLONE THAT WILL PROVIDE A FLOW MORE IN STEP WITH THE
LOWER STEERING WINDS.  UNLIKE THE RECENT MODEL RUNS WITH
CHANTAL...IN WHICH A FAVORABLE UPPER ENVIRONMENT WAS FORECAST TO
DEVELOP BUT NEVER REALLY DID...THE UPPER HIGH IS ALREADY IN PLACE
HERE AND DEAN MERELY NEEDS TO MOVE INTO THE RIGHT PLACE.  HOWEVER...
THERE IS ALSO A DISTINCT POSSIBILITY THAT THE SYSTEM WILL NOT
SURVIVE LONG ENOUGH TO TAKE ADVANTAGE.  THE OFFICIAL INTENSITY
FORECAST...WHICH MAKES DEAN A HURRICANE IN 36 HOURS...PRESUMES THAT
THE SYSTEM WILL SURVIVE THE NEXT 12.

TRACK GUIDANCE IS DIVERGENT...AND WITH THE COMPLICATED UPPER FLOW 
PATTERNS THE FUTURE PATH OF DEAN WILL BE STRONGLY DEPENDENT ON THE 
INTENSITY.  A DEEPER SYSTEM COULD MOVE MORE TO THE WEST UNDER THE 
UPPER HIGH AND RECURVE RELATIVELY SLOWLY...WHILE A WEAK SYSTEM IS 
MORE LIKELY TO HIT THE TROUGH OFF THE EAST COAST SOONER AND 
ACCELERATE NORTHEASTWARD.  IN EITHER CASE...DEAN IS NOT EXPECTED TO 
BE A THREAT TO THE U.S. MAINLAND.
 
FORECASTER FRANKLIN
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     23/0300Z 20.2N  68.1W    50 KTS
12HR VT     23/1200Z 21.5N  70.2W    50 KTS
24HR VT     24/0000Z 23.1N  72.3W    55 KTS
36HR VT     24/1200Z 25.1N  72.5W    65 KTS
48HR VT     25/0000Z 27.0N  72.0W    70 KTS
72HR VT     26/0000Z 30.5N  69.5W    75 KTS
 
 
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