Tropical Storm BERTHA

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TROPICAL STORM BERTHA DISCUSSION NUMBER   8
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL022008
1100 PM EDT FRI JUL 04 2008

MICROWAVE IMAGERY OVER THE LAST 12-24 HOURS INDICATES THAT BERTHA
HAS BEEN STAIR-STEPPING ITS WAY ACROSS THE ATLANTIC OSCILLATING
BETWEEN A WESTWARD AND NORTHWESTWARD HEADING WITH EACH NEW
CONVECTIVE BURST.  IRONING ALL THIS OUT YIELDS AN INITIAL MOTION
ESTIMATE OF 280/18...A LITTLE FASTER THAN BEFORE.  THERE HAS BEEN
LITTLE OVERALL CHANGE IN THE FORECAST PHILOSOPHY.  A STRONG RIDGE
TO THE NORTH SHOULD KEEP THE CYCLONE ON A GENERAL WESTWARD TO WEST-
NORTHWESTWARD MOTION DURING THE NEXT 2-3 DAYS.  WHILE MOST OF THE
DYNAMICAL MODELS STILL SHOW A WEAKNESS DEVELOPING IN THE RIDGE
NORTH OF BERTHA IN ABOUT THREE DAYS...THEY HAVE BEEN TRENDING
TOWARDS A MORE WESTWARD MOTION OF BERTHA DUE TO A WEAKER AND
SHALLOWER DEPICTION OF THE CYCLONE.  THE EXCEPTION IS THE HWRF
WHICH FORECASTS A STRONGER AND DEEPER BERTHA TURNING NORTHWESTWARD
BEYOND 72 HOURS DUE TO THE WEAKNESS.  THE OFFICIAL FORECAST IS
NUDGED A LITTLE WESTWARD BUT IS STILL NORTH OF MOST OF THE GUIDANCE
SINCE ONLY A MODEST INCREASE IN STRENGTH WOULD ALLOW BERTHA TO
RESPOND TO THE DEEPER AND MORE NORTHWARD STEERING.    
 
BERTHA CONTINUES TO EXHIBIT A CONVECTIVE BURSTING PATTERN WITH THE
LATEST BURST BEGINNING AROUND 2300 UTC.  AVAILABLE SATELLITE
INTENSITY ESTIMATES SUGGEST THAT THE SYSTEM HAS CHANGED LITTLE IN
STRENGTH WITH THE INITIAL INTENSITY HELD AT 45 KT. BERTHA IS
FORECAST TO MOVE OVER MARGINALLY WARM SSTS DURING THE NEXT 24 HOURS
WHICH IS EXPECTED TO LIMIT INTENSIFICATION.  THEREAFTER...SSTS
GRADUALLY INCREASE ALONG THE PROJECTED TRACK AND BERTHA IS EXPECTED
TO SLOWLY STRENGTHEN.  VERTICAL SHEAR IS FORECAST TO INCREASE
TOWARDS THE END OF THE FORECAST SO ARRESTED DEVELOPMENT IS SHOWN
BEYOND 72 HOURS.  THIS FORECAST IS SIMILAR TO THE PREVIOUS ONE AND
IS IN CLOSEST AGREEMENT WITH THE HWRF MODEL. 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      05/0300Z 16.0N  33.5W    45 KT
 12HR VT     05/1200Z 16.4N  36.2W    45 KT
 24HR VT     06/0000Z 17.0N  39.8W    45 KT
 36HR VT     06/1200Z 17.6N  43.6W    50 KT
 48HR VT     07/0000Z 18.1N  47.3W    55 KT
 72HR VT     08/0000Z 20.0N  53.5W    60 KT
 96HR VT     09/0000Z 22.0N  58.5W    60 KT
120HR VT     10/0000Z 24.0N  63.0W    60 KT
 
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FORECASTER RHOME
 
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