Tropical Storm BERTHA

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TROPICAL STORM BERTHA DISCUSSION NUMBER  49
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL022008
500 AM EDT TUE JUL 15 2008
 
BERTHA HAS PUT A LITTLE MORE DISTANCE BETWEEN ITSELF AND
BERMUDA...AND THE PREVIOUSLY FORECAST TURN TOWARD THE RIGHT IS
MATERIALIZING. THE INITIAL MOTION ESTIMATE IS 030/8...BUT THE
HEADING WILL LIKELY CHANGE ALMOST CONTINUOUSLY DURING THE NEXT
COUPLE OF DAYS...DURING WHICH TIME BERTHA IS FORECAST BY NEARLY ALL
OF THE MODELS TO KEEP TURNING RIGHT. WATER VAPOR IMAGERY
SHOWS THAT A MID-LATITUDE TROUGH IS ABOUT TO EXIT THE U.S. EAST
COAST AND GIVE BERTHA A SHOVE TO THE EAST...BUT ALSO A LARGE CUTOFF
LOW CLOSING IN ON BERTHA FROM THE OTHER DIRECTION. ONCE BERTHA AND
THE CUTOFF LOW MEET UP DURING THE NEXT COUPLE OF DAYS...THE
GUIDANCE INDICATES BERTHA WILL THEN FOLLOW AN UNDULATING TRACK. THE
OFFICIAL FORECAST MOTION IS SHARPLY SOUTHEASTWARD ON DAY TWO...THEN
GENERALLY NORTHEASTWARD ON DAYS 3-5 AS THE CUTOFF LOW IS FORECAST
TO LIFT OUT AGAIN...ALL IN GENERAL AGREEMENT WITH MOST MODELS. THE
MODELS DO NOT AGREE...HOWEVER...ON THE FORWARD SPEED OF BERTHA ON
DAYS 3-5...IN PART DUE TO VARYING DEPICTIONS OF BERTHA'S DEPTH AND
STRENGTH. THE NEW OFFICIAL TRACK IS SIMILAR TO THE PREVIOUS ONE AND
PRESUMES THAT BERTHA WILL BE WEAKER BY THAT TIME AND NOT ACCELERATE
AS QUICKLY NORTHEASTWARD AS THE GFDL AND HWRF ARE SUGGESTING...AND
INSTEAD RELIES MAINLY ON A BLEND OF THE GFS AND ECMWF.

THE INITIAL AND FORECAST INTENSITIES ARE UNCHANGED.  THE SATELLITE
APPEARANCE OF BERTHA REMAINS MUCH AS IT WAS A FEW HOURS AGO...AND
DVORAK ESTIMATES GENERALLY SUPPORT KEEPING THE INITIAL INTENSITY AT
60 KT.  BERTHA HAS AN OPPORTUNITY TO STRENGTHEN DURING THE NEXT
COUPLE OF DAYS AS IT REMAINS OVER SEA-SURFACE TEMPERATURES BETWEEN
26 AND 27 CELSIUS...BUT SIGNIFICANT STRENGTHENING DOES NOT APPEAR
LIKELY GIVEN THE SPRAWLING NATURE OF THE SYSTEM.  BEYOND 48
HOURS...GRADUAL WEAKENING IS AGAIN FORECAST DUE TO COOLER WATERS
AND A STRONG POSSIBILITY OF INCREASING SHEAR.  THAT SCENARIO IS THE
ONE PAINTED BY THE SHIPS AND LGEM GUIDANCE...WHICH DIFFERS FROM THE
GFDL AND HWRF...BOTH OF WHICH FORECAST BERTHA TO REMAIN A HURRICANE
FOR MUCH OF THE NEXT FIVE DAYS.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      15/0900Z 34.7N  63.2W    60 KT
 12HR VT     15/1800Z 35.7N  62.3W    65 KT
 24HR VT     16/0600Z 35.9N  60.9W    65 KT
 36HR VT     16/1800Z 34.7N  59.8W    65 KT
 48HR VT     17/0600Z 33.7N  58.6W    65 KT
 72HR VT     18/0600Z 34.0N  55.0W    60 KT
 96HR VT     19/0600Z 37.0N  51.0W    55 KT
120HR VT     20/0600Z 41.0N  47.0W    50 KT
 
$$
FORECASTER KNABB
 
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