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| #199740 (Received by flhurricane at: 4:55 PM 07.Jul.2008) TCDAT2 HURRICANE BERTHA DISCUSSION NUMBER 19 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022008 500 PM EDT MON JUL 07 2008 BERTHA'S SATELLITE PRESENTATION HAS CONTINUED TO IMPROVE THIS AFTERNOON WITH A VERY DISTINCT EYE NOW SURROUNDED BY A RING OF COLD CLOUD TOPS. SUBJECTIVE DVORAK T NUMBERS WERE UNANIMOUSLY 5.0 BUT OBJECTIVE NUMBERS HAVE INCREASED TO 6.0 FOR THE PAST 3 HOURS. THIS SUPPORTS AN INITIAL INTENSITY OF 100 KT MAKING BERTHA A MAJOR CATEGORY THREE HURRICANE ON THE SAFFIR-SIMPSON HURRICANE SCALE. BERTHA'S INTENSIFICATION TO MAJOR HURRICANE TODAY HIGHLIGHTS THE DIFFICULTIES OF FORECASTING RAPID INTENSITY CHANGES. IN THE SHORT-TERM...SHEAR IS EXPECTED TO BE LOW AND THE INTENSITY WILL BE PRIMARILY CONTROLLED BY EYEWALL CYCLES. AS A RESULT...SOME FLUCTUATIONS IN INTENSITY ARE LIKELY. IN A DAY OR TWO...THE GFS MODEL STILL INDICATES INCREASING SHEAR. THE SHIPS AND LGEM STATISTICAL MODELS...WHICH BASE THEIR SHEAR ESTIMATES FROM THE GFS...SHOW WEAKENING BEYOND 24 HOURS AND SO DOES THE OFFICIAL FORECAST. BERTHA HAS BEEN MOVING MORE TOWARDS THE NORTHWEST DURING THE LAST COUPLE OF HOURS WITH A REDUCTION IN FORWARD SPEED...BOTH INDICATIONS THAT THE HURRICANE HAS REACHED THE MUCH-ANTICIPATED WEAKNESS IN THE RIDGE. SINCE BERTHA COULD BE WOBBLING...THE INITIAL MOTION ESTIMATE BASED ON A 12 HOUR AVERAGE IS 300/10. TRACK GUIDANCE REMAINS IN GOOD AGREEMENT ON A GRADUAL NORTHWARD TURN DURING THE NEXT 2-3 DAYS. THEREAFTER...GLOBAL MODELS SUGGEST THAT THE STEERING CURRENTS COULD BECOME WEAK LEADING TO INCREASED UNCERTAINTY IN THE TRACK FORECAST. EVEN THOUGH THE OFFICIAL FORECAST IS SHIFTED A LITTLE TO THE EAST...IT IS STILL WAY TOO SOON TO DETERMINE WHETHER OR NOT BERTHA WILL AFFECT BERMUDA. FORECAST POSITIONS AND MAX WINDS INITIAL 07/2100Z 20.1N 52.1W 100 KT 12HR VT 08/0600Z 20.8N 53.5W 100 KT 24HR VT 08/1800Z 21.7N 55.4W 95 KT 36HR VT 09/0600Z 22.9N 57.3W 90 KT 48HR VT 09/1800Z 24.0N 59.0W 85 KT 72HR VT 10/1800Z 26.5N 61.5W 80 KT 96HR VT 11/1800Z 29.0N 62.5W 75 KT 120HR VT 12/1800Z 31.5N 62.5W 75 KT $$ FORECASTER RHOME |
