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| #201111 (Received by flhurricane at: 5:08 AM 15.Jul.2008) TCDAT2 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 |
