Hurricane BERTHA

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HURRICANE BERTHA DISCUSSION NUMBER  67
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL022008
500 PM EDT SAT JUL 19 2008
 
RELATIVELY DEEP CONVECTION PERSISTS ALL THE WAY AROUND THE
CIRCULATION CENTER...AND DVORAK ESTIMATES AT 18Z SUPPORT
MAINTAINING BERTHA AS A HURRICANE WITH MAXIMUM WINDS OF 65 KT. 
BERTHA IS CROSSING THE 20 DEGREE CELSIUS ISOTHERM...HOWEVER...AND
IT SEEMINGLY CANNOT HOLD ON TO TROPICAL CHARACTERISTICS MUCH
LONGER.  THE OFFICIAL FORECAST PRESUMES THAT EXTRATROPICAL
TRANSITION WILL BE WELL UNDERWAY...ALTHOUGH PERHAPS NOT
COMPLETE...BY 12 HOURS AS THE SYSTEM REACHES 17 CELSIUS
WATERS...BUT AFTER THAT THE SYSTEM SHOULD BE FULLY EXTRATROPICAL. 
THIS EVOLUTION IS CONSISTENT WITH THE FSU PHASE SPACE ANALYSIS BASED
ON THE GFS GLOBAL MODEL.  DESPITE THE TRANSITION...THE WINDS WILL
PROBABLY NOT FALL OFF VERY FAST...AND BERTHA WILL BE A LARGE AND
POWERFUL EXTRATROPICAL CYCLONE FOR TWO TO THREE DAYS UNTIL IT IS
ABSORBED BY OR MERGES WITH ANOTHER SYSTEM CROSSING CANADA.

THERE HAS BEEN NO DETECTABLE CHANGE TO THE INITIAL MOTION ESTIMATE
OF 035/22.  A GRADUAL INCREASE IN FORWARD SPEED IS FORECAST...ALONG
ABOUT THE SAME HEADING...IN CLOSE AGREEMENT WITH THE GFS MODEL. 
THE NEW OFFICIAL TRACK IS VERY SIMILAR TO THE PREVIOUS ADVISORY.

 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      19/2100Z 44.8N  43.3W    65 KT
 12HR VT     20/0600Z 47.9N  40.0W    60 KT
 24HR VT     20/1800Z 52.9N  34.3W    55 KT...EXTRATROPICAL
 36HR VT     21/0600Z 58.0N  27.2W    50 KT...EXTRATROPICAL
 48HR VT     21/1800Z 62.5N  20.0W    50 KT...EXTRATROPICAL
 72HR VT     22/1800Z...DISSIPATED
 
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FORECASTER KNABB
 
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