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| #201546 (Received by flhurricane at: 11:08 PM 17.Jul.2008) TCDAT2 TROPICAL STORM BERTHA DISCUSSION NUMBER 60 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022008 1100 PM EDT THU JUL 17 2008 BERTHA CONTINUES TO BE A RELENTLESS CYCLONE AS A NEW BURST OF DEEP CONVECTION RECENTLY FORMED OVER THE SOUTHEASTERN SEMICIRCLE THUS MAINTAINING THE OVERALL SATELLITE APPEARANCE. BASED ON THIS...THE INITIAL INTENSITY IS HELD AT 50 KT FOR THIS ADVISORY. WHILE VERTICAL SHEAR IS EXPECTED TO REMAIN RELATIVELY LOW FOR THE NEXT DAY OR SO...BERTHA IS EXPECTED TO MOVE OVER INCREASINGLY COLDER WATERS. THIS SHOULD RESULT IN WEAKENING IN THE SHORT-TERM. BEYOND 48 HOURS...BAROCLINIC DYNAMICS AND POSSIBLE EXTRATROPICAL TRANSITION COULD RESULT IN SOME RESTRENGTHENING. HOWEVER...THERE ARE DIFFERENCES AMONG THE VARIOUS DYNAMICAL MODELS WITH SOME MODELS SHOWING BERTHA BECOMING A LARGE AND POWERFUL EXTRATROPICAL SYSTEM WHILE OTHER MODELS SHOW A WEAKENING CYCLONE BEING ABSORBED INTO A LARGER NON-TROPICAL LOW. GIVEN THIS UNCERTAINTY...THE OFFICIAL FORECAST SHOWS SLOW WEAKENING EARLY WITH A LITTLE RESTRENGTHENING AT DAYS 4 AND 5. BERTHA CONTINUES TO ROTATE AROUND A MIDDLE TO UPPER LEVEL LOW RESULTING IN A TURN TOWARDS THE EAST...AND THE INITIAL MOTION IS NOW 100/15. THE CYCLONE IS EXPECTED TO TURN NORTHEASTWARD AND ACCELERATE DURING THE NEXT DAY OR SO AS IT COMPLETES ITS ROTATION AROUND THE LOW AND THEN ENCOUNTERS STRONG SOUTHWESTERLY FLOW AHEAD OF A MID-LATITUDE TROUGH MOVING OFF THE CANADIAN MARITIMES. AS WOULD BE EXPECTED WITH AN ACCELERATING CYCLONE...TRACK GUIDANCE DIVERGES QUITE A BIT DUE TO THEIR DIFFERENT FORWARD SPEEDS. IN GENERAL...TRACK GUIDANCE IS FASTER THAN BEFORE BUT THEY HAVE NOT DEMONSTRATED GOOD RUN TO RUN CONSISTENCY. THE OFFICIAL FORECAST IS NUDGED TOWARDS THE CONSENSUS OF THE DYNAMICAL MODELS WHICH RESULTS IN A SLIGHTLY FASTER TRACK FORECAST THAN BEFORE. FORECAST POSITIONS AND MAX WINDS INITIAL 18/0300Z 33.9N 55.4W 50 KT 12HR VT 18/1200Z 34.8N 53.7W 50 KT 24HR VT 19/0000Z 36.7N 51.2W 45 KT 36HR VT 19/1200Z 38.8N 48.6W 45 KT 48HR VT 20/0000Z 41.2N 45.2W 40 KT 72HR VT 21/0000Z 47.0N 36.5W 45 KT...EXTRATROPICAL 96HR VT 22/0000Z 56.0N 24.0W 45 KT...EXTRATROPICAL 120HR VT 23/0000Z...ABSORBED $$ FORECASTER RHOME |
