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HURRICANE LENNY DISCUSSION NUMBER  21
NATIONAL WEATHER SERVICE MIAMI FL
10 AM EST THU NOV 18 1999
 
SAN JUAN WSR-88D INDICATES THAT LENNY HAS BEEN NEARLY STATIONARY
DURING THE PAST FEW HOURS.  BECAUSE STEERING CURRENTS ARE EXPECTED
TO REMAIN WEAK DURING THE NEXT 12 HOURS OR SO...NO SIGNIFICANT
MOTION IS INDICATED THROUGH THAT PERIOD.  WV IMAGES SHOW AN EASTWARD
MOVING SHORT WAVE CURRENTLY LOCATED OVER THE EASTERN UNITED STATES.
THIS FEATURE MAY PRODUCE AN INCREASE IN THE SOUTHWESTERLY FLOW NEAR
THE HURRICANE DURING THE NEXT COUPLE OF DAYS...FORCING LENNY TO MOVE
TOWARD THE NORTHEAST LATER IN THE FORECAST PERIOD AS INDICATED IN
THE OFFICIAL FORECAST.  THIS IS THE GENERAL SOLUTION PROVIDED BY
MOST OF THE TRACK AND GLOBAL MODELS WITH THE EXCEPTION OF THE
RELIABLE AND GOOD PERFORMER UK MODEL WHICH KEEPS THE HURRICANE ON A
SLOW NORTHWARD TRACK.  ON THE UK MODEL...THE SHORTWAVE BYPASSES THE
HURRICANE...KEEPING LENNY SOUTH OF 25 DEGREES NORTH FOR AT LEAST 3
OR 4 DAYS.
 
THE EYE IS NOT LONGER VISIBLE ON SATELLITE IMAGES BUT IT IS WELL
DEFINED ON RADAR. BECAUSE BOTH THE CENTRAL PRESSURE HAS BEEN RISING
AND DVORAK T-NUMBERS ARE LOWER THAT YESTERDAY...INITIAL INTENSITY
IS 115 KNOTS. THERE IS NO SHEAR OVER THE SYSTEM AND PERHAPS ONLY
UPWELLING IS CAUSING WEAKENING AT THIS TIME. SOME FLUCTUATIONS IN
INTENSITY ARE FORECAST DURING THE NEXT DAY OR SO. THEREAFTER
...WEAKENING IS INDICATED AS LENNY MOVES TOWARD A LESS
FAVORABLE UPPER-LEVEL WIND ENVIRONMENT.  IF THE THERMODYNAMICS ARE
PROPERLY ESTABLISHED...A PARAMETER I DO NOT KNOW TO FORECAST...THE
HURRICANE COULD OVERCOME THE SHEARING EFFECTS AND REMAIN STRONG A
LITTLE BIT LONGER.
 
BECAUSE OF THE SIZE OF THE HURRICANE AND THE TRACK FORECAST
UNCERTAINTIES...ONE MUST NOT FOCUS ON THE EXACT FORECAST TRACK.
 
AVILA
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     18/1500Z 17.8N  63.6W   115 KTS
12HR VT     19/0000Z 18.0N  63.5W   115 KTS
24HR VT     19/1200Z 18.5N  62.5W   115 KTS
36HR VT     20/0000Z 19.3N  61.8W   105 KTS
48HR VT     20/1200Z 20.0N  61.0W    85 KTS
72HR VT     21/1200Z 22.0N  59.0W    65 KTS
 
 
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