Tropical Storm BERTHA

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TROPICAL STORM BERTHA DISCUSSION NUMBER  53
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL022008
500 AM EDT WED JUL 16 2008
 
BERTHA IS CAUGHT BETWEEN MIDDLE TO UPPER-LEVEL SOUTHWESTERLY FLOW
AHEAD OF A TROUGH OVER THE EASTERN UNITED STATES AND NORTHERLY FLOW
ON THE WEST SIDE OF AN UPPER-LOW OVER THE CENTRAL ATLANTIC. THIS
HAS RESULTED IN BERTHA'S CLOUD PATTERN BECOMING INCREASINGLY
STRETCHED IN A SOUTHEAST TO NORTHWEST ORIENTATION. HOWEVER...THE
DVORAK INTENSITY ESTIMATES STILL SUPPORT 55 KT. BERTHA IS BEGINNING
AN ANTICIPATED TURN TOWARD THE SOUTH AND THIS TRACK IS EXPECTED TO
TAKE THE CYCLONE OVER PROGRESSIVELY WARMER WATERS DURING THE NEXT 2
DAYS. SINCE THE SHEAR IS EXPECTED TO REMAIN LOW DURING THIS
PERIOD...SOME RESTRENGTHENING IS POSSIBLE PRIOR TO THE CYCLONE
ENCOUNTERING COOLER WATER AND INCREASING VERTICAL SHEAR BEYOND 72
HOURS. THE NEW OFFICIAL INTENSITY FORECAST IS VERY SIMILAR TO THE
PREVIOUS ONE AND SHOWS BERTHA REMAINING JUST SHY OF HURRICANE
STRENGTH. 
 
BERTHA IS NOW MOVING TOWARD THE EAST-SOUTHEAST WITH AN INITIAL
MOTION ESTIMATE OF 100/05.  A SOUTHEAST TURN IS EXPECTED LATER
TODAY FOLLOWED BY A TURN EASTWARD AND NORTHEASTWARD IN 2-3 DAYS AS
THE CYCLONE CYCLONICALLY ROTATES AROUND A LARGE UPPER-LOW TO ITS
EAST. TRACK GUIDANCE IS IN GOOD AGREEMENT DURING THE FIRST 2 DAYS OF
THE FORECAST BUT THEN DIVERGES AT DAYS 3-5.  THE GUIDANCE ENVELOPE
SPANS NEARLY 1400 MILES AT DAY 5 AND IS BOUNDED BY THE NOGAPS
MODEL...WHICH RACES THE CYCLONE NORTHEASTWARD...AND THE GFS
MODEL...WHICH SHOWS A MUCH SLOWER EAST-NORTHEASTWARD MOTION.  THE
HWRF...GFDL...AND UKMET MODELS LIE IN BETWEEN THESE OUTLIER
SOLUTIONS AND ARE THE BASIS FOR THE SOUTHWARD SHIFT AND SLOWER
FORWARD SPEED SHOWN IN THE NEW OFFICIAL FORECAST. 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      16/0900Z 36.4N  61.0W    55 KT
 12HR VT     16/1800Z 36.1N  60.6W    55 KT
 24HR VT     17/0600Z 35.0N  60.0W    60 KT
 36HR VT     17/1800Z 34.1N  58.6W    60 KT
 48HR VT     18/0600Z 34.0N  56.5W    60 KT
 72HR VT     19/0600Z 36.5N  52.0W    50 KT
 96HR VT     20/0600Z 40.0N  47.0W    45 KT
120HR VT     21/0600Z 43.5N  41.0W    40 KT...EXTRATROPICAL
 
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FORECASTER RHOME
 
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