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HURRICANE LENNY DISCUSSION NUMBER  18
NATIONAL WEATHER SERVICE MIAMI FL
4 PM EST WED NOV 17 1999
 
LENNY CONTINUES TO MOVE ON A GENERAL NORTHEASTWARD TRACK ABOUT 8
KNOTS.  BECAUSE THE STEERING CURRENTS CONTROLLING THE PATH OF THE
HURRICANE ARE NOT EXPECTED TO CHANGE...THIS GENERAL NORTHEASTWARD
MOTION IS FORECAST TO CONTINUE THROUGH 72 HOURS.  THIS IS CONSISTENT
WITH MOST THE TRACK AND GLOBAL MODELS AND PREVIOUS FORECASTS.
 
THE SIGNIFICANT EVENT OF THE DAY IS THE UNEXPECTED INTENSIFICATION
OF LENNY...INDICATING THAT THERE IS LITTLE SKILL IN FORECASTING
RAPID INTENSITY CHANGES.  THE CENTRAL PRESSURE EXTRAPOLATED FROM 700
MB HAS FALLEN TO 927 MB WHILE A DROP MEASURED 934 MB.  THE 
FLIGHT-LEVEL WINDS HAVE INCREASED TO 149 KNOTS.  THE MEAN BOUNDARY
LAYER WINDS FROM DROPSONDES ARE 155 KNOTS AND PEAK WINDS REACHED 180
KNOTS AT THE 891-MB LEVEL A COUPLE OF HOURS AGO.  BASED ON THAT
INFORMATION...INITIAL INTENSITY WAS ADJUSTED TO 130 KNOTS.
LENNY IS VERY CLOSE TO BEING A CATEGORY FIVE HURRICANE ON THE
SAFFIR/SIMPSON SCALE.  HURRICANES NORMALLY DO NOT STAY WITH SUCH
STRENGTH FOR A LONG TIME...THEREFORE SOME FLUCTUATIONS IN INTENSITY
ARE ANTICIPATED DURING THE NEXT 12 TO 24 HOURS.  THEREAFTER...A
GRADUAL WEAKENING IS EXPECTED AS LENNY MOVES INTO A LESS FAVORABLE
UPPER-LEVEL ENVIRONMENT.
 
BECAUSE OF THE SIZE OF THE HURRICANE AND THE TRACK FORECAST
UNCERTAINTIES...ONE MUST NOT FOCUS ON THE EXACT FORECAST TRACK.
 
BECAUSE OF THE CONTINUED EASTWARD MOTION...THE HURRICANE WARNING FOR
MAINLAND PUERTO RICO HAS BEEN DOWNGRADED TO TROPICAL STORM WARNING
BUT NOT FOR CULEBRA AND VIEQUES.
 
AVILA
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     17/2100Z 17.6N  64.3W   130 KTS
12HR VT     18/0600Z 18.4N  63.5W   130 KTS
24HR VT     18/1800Z 19.7N  62.3W   120 KTS
36HR VT     19/0600Z 21.0N  61.5W   100 KTS
48HR VT     19/1800Z 22.5N  60.5W    85 KTS
72HR VT     20/1800Z 25.0N  59.0W    65 KTS
 
 
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