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HURRICANE LENNY DISCUSSION NUMBER  20
NATIONAL WEATHER SERVICE MIAMI FL
4 AM EST THU NOV 18 1999
 
DATA FROM THE SAN JUAN WSR-88D AND AIR FORCE RESERVE HURRICANE
HUNTER AIRCRAFT INDICATE THAT LENNY IS DRIFTING EAST..080/03. WHILE
THE CENTRAL PRESSURE HAS RISEN TO 947 MB...700 MB WINDS HAVE BEEN AS
HIGH AS 145 KT. AN EYEWALL DROPSONDE INDICATED 132 KT NEAR THE
SURFACE. BASED ON THIS...THE INITIAL INTENSITY REMAINS 125 KT.
 
LENNY IS CURRENT LOCATED BETWEEN A MID/UPPER LEVEL RIDGE TO THE
SOUTHEAST AND A BUILDING LOW/MID LEVEL TO THE NORTH...WHICH MAY BE
CAUSING THE CURRENT SLOWER MOTION. MODEL GUIDANCE HAS BECOME QUITE
DIVERSE...FROM THE UKMET SHOWING A SLOW NORTHWARD DRIFT TO THE BAMD
MOVING THE STORM EASTWARD. A SHORTWAVE TROUGH SEEN IN WATER VAPOR
IMAGERY OVER THE SOUTHEASTERN U.S. MAY COME CLOSE ENOUGH TO LENNY TO
NUDGE IT NORTHEASTWARD...AND THE OFFICIAL FORECAST IS BASED ON THIS
AND SOME CONTINUITY FROM THE PREVIOUS FORECAST. AN ALTERNATIVE
SCENARIO WOULD BE VERY LITTLE MOTION OVER THE NEXT THREE DAYS.

LENNY IS STILL OVER WARM WATER AND IS SOUTH OF THE STRONG UPPER
LEVEL WESTERLIES. THEREFORE...ANY FURTHER WEAKENING SHOULD BE SLOW.
THE AVN AND UKMET ARE FORECASTING STRONG WESTERLIES TO CONTINUE
NORTH OF 20N. IF THE FORECAST NORTHEASTWARD MOTION OCCURS...THE
SHEAR SHOULD INCREASE AFTER 36 HOURS ALONG WITH COOLING SEA SURFACE
TEMPERATURES...WHICH SHOULD CAUSE SIGNIFICANT WEAKENING.

FORECAST WIND RADII HAVE BEEN EXPANDED ON THE NORTH SIDE OF THE
HURRICANE IN ANTICIPATION OF THE LOW LEVEL RIDGE INCREASING THE
PRESSURE GRADIENT THERE.
 
BECAUSE OF THE SIZE OF THE HURRICANE AND THE TRACK FORECAST
UNCERTAINTIES...ONE MUST NOT FOCUS ON THE EXACT FORECAST TRACK.
 
AS A RESULT OF THE SLOW MOTION...TROPICAL STORM WARNINGS REMAIN IN
EFFECT FOR THE EASTERN PORTIONS OF PUERTO RICO WHILE HURRICANE
WARNING REMAIN POSTED FOR CULEBRA AND VIEQUES...AND THE U.S. AND
BRITISH VIRGIN ISLANDS.
 
BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     18/0900Z 17.8N  63.6W   125 KTS
12HR VT     18/1800Z 17.9N  63.3W   125 KTS
24HR VT     19/0600Z 18.4N  62.6W   120 KTS
36HR VT     19/1800Z 19.1N  61.9W   105 KTS
48HR VT     20/0600Z 20.0N  61.0W    85 KTS
72HR VT     21/0600Z 22.0N  59.0W    65 KTS
 
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