Tropical Storm BERTHA

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TROPICAL STORM BERTHA DISCUSSION NUMBER  44
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL022008
1100 PM EDT SUN JUL 13 2008

IT APPEARS THAT BERTHA IS TAPPING LIGHTLY ON THE ACCELERATOR...WITH
AN INITIAL MOTION ESTIMATE OF 335/3.  MOST OF THE MODELS FORECAST A
GRADUAL INCREASE IN BERTHA'S FORWARD SPEED WITH A SUBTLE TURN TO
THE RIGHT DURING THE NEXT COUPLE OF DAYS...AROUND A WEAK MID-LEVEL
HIGH CURRENTLY JUST EAST OF THE STORM.  BY THAT TIME THE MODELS
FORECAST BERTHA TO BE NORTH OF THE RIDGE...AND IN BETWEEN A
MID-LATITUDE TROUGH NEAR THE NORTHEAST U.S. COAST AND A CUTOFF LOW
OVER THE CENTRAL NORTH ATLANTIC.  BERTHA AND THE CUTOFF LOW ARE
THEN FORECAST TO INTERACT WITH ONE ANOTHER IN A POTENTIALLY COMPLEX
MANNER ON DAYS 3 THROUGH 5...ALTHOUGH A GENERALLY EASTWARD MOTION
WITHIN THE MID-LATITUDE WESTERLIES IS IMPLIED BY THE MODEL
CONSENSUS.  THE UNUSUAL UNDULATIONS IN THE OFFICIAL TRACK BEYOND 48
HOURS ARE SUPPORTED BY ALL OF THE DYNAMICAL MODELS...BUT THE DIPS
AND TURNS IN THE MODEL TRACKS ARE A BIT MORE EXTREME THAN SHOWN IN
THE OFFICIAL FORECAST.  THERE IS ALSO GREAT DISAGREEMENT IN THE
GUIDANCE ON THE FORWARD SPEED OF BERTHA DURING THAT TIME
FRAME...BUT THE FIVE-DAY CONSENSUS POINT IS NOT FAR FROM THAT IN
THE PREVIOUS ADVISORY...SO ON BALANCE THE NEW TRACK IS NOT THAT
MUCH OF A CHANGE.

I HAVE NO SOLID REASON TO ALTER THE INITIAL INTENSITY OF 55 KT...AS
THE SUBJECTIVE DVORAK ESTIMATES HAVE NOT CHANGED MUCH...AND A
QUIKSCAT OVERPASS AROUND 23Z ONLY CAPTURED THE WESTERN HALF OF THE
CIRCULATION.  CLOUD TOPS OF THE OUTER BANDS HAVE WARMED DURING THE
PAST FEW HOURS...BUT IF ANYTHING THE CONVECTION NEAR THE CENTER HAS
INCREASED EVER SO SLIGHTLY.  A CONSENSUS OF THE VARIOUS INTENSITY
MODELS DOES NOT SUGGEST MUCH CHANGE IN BERTHA'S STRENGTH DURING THE
NEXT SEVERAL DAYS AS IT PASSES OVER GRADUALLY COOLER SEA-SURFACE
TEMPERATURES.  THE NEW OFFICIAL FORECAST HOLDS ON TO THE CURRENT
INTENSITY THROUGH 36 HOURS AND ONLY SHOWS A SLIGHTLY WEAKER SYSTEM
BEYOND THAT TIME.  THIS FORECAST IS VERY CLOSE TO THE SHIPS AND
LGEM...BUT STILL BELOW THE GFDL AND HWRF THAT FORECAST BERTHA TO
AGAIN BECOME A HURRICANE.  WHILE THAT POSSIBILITY CANNOT BE RULED
OUT...IT APPEARS TO BE THE LESS LIKELY OPTION...ESPECIALLY GIVEN
THE CONVOLUTED STATE OF BERTHA'S INNER CORE.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      14/0300Z 30.5N  63.1W    55 KT
 12HR VT     14/1200Z 31.5N  63.5W    55 KT
 24HR VT     15/0000Z 33.0N  63.6W    55 KT
 36HR VT     15/1200Z 34.6N  63.1W    55 KT
 48HR VT     16/0000Z 35.8N  62.0W    50 KT
 72HR VT     17/0000Z 35.5N  59.5W    50 KT
 96HR VT     18/0000Z 34.5N  56.5W    50 KT
120HR VT     19/0000Z 35.5N  53.0W    50 KT
 
$$
FORECASTER KNABB
 
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