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| #200571 (Received by flhurricane at: 4:58 AM 12.Jul.2008) TCDAT2 HURRICANE BERTHA DISCUSSION NUMBER 37 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022008 500 AM EDT SAT JUL 12 2008 INFRARED SATELLITE IMAGERY SUGGESTS THAT THE INNER EYEWALL REMNANT OF BERTHA IS FINALLY DISSIPATING...WITH THE CLOUD TOPS COOLING IN THE LARGE OUTER EYEWALL. SATELLITE INTENSITY ESTIMATES REMAIN UNCHANGED FROM 6 HR AGO...AND BASED ON THIS AND PERSISTENCE FROM THE PREVIOUS ADVISORY THE INITIAL INTENSITY REMAINS 80 KT. THE CIRRUS OUTFLOW REMAINS GOOD IN THE SOUTHERN SEMICIRCLE BUT HAS DECREASED SOMEWHAT IN THE NORTHERN SEMICIRCLE. THE INITIAL MOTION IS 340/4...AND THE 4 KT FORWARD SPEED COULD BE GENEROUS. BERTHA IS CURRENTLY EMBEDDED IN THE SUBTROPICAL RIDGE IN AN AREA OF WEAK STEERING FLOW...WITH A MID/UPPER-LEVEL SHORTWAVE TROUGH AND ASSOCIATED SURFACE COLD FRONT PASSING TO THE NORTH OF THE HURRICANE. THE LARGE-SCALE MODELS FORECAST THE TROUGH TO BYPASS BERTHA WITH A MID-LEVEL SHORTWAVE RIDGE FORMING NORTH OF THE HURRICANE. THE ECMWF...NOGAPS...AND CANADIAN MODEL RESPOND TO THIS BY JOGGING BERTHA TO THE WEST CLOSER TO BERMUDA....WHILE THE GFS... HWRF..AND GFDL CALL FOR A NORTHWARD MOTION A LITTLE FARTHER TO THE EAST. THIS PORTION OF THE NEW FORECAST TRACK CALLS FOR A NORTHWARD MOTION FOR ABOUT 72 HR...WITH THE 48-72 HR POSITION A LITTLE TO THE WEST OF THE PREVIOUS TRACK IN DEFERENCE TO THE MODELS FORECASTING A WESTWARD JOG. AFTER 72 HR...THE LARGE-SCALE MODELS FORECAST THAT A NEW TROUGH OVER THE EASTERN UNITED STATES WILL BE STRONG ENOUGH TO LIFT BERTHA TO THE NORTHEAST OR EAST AT A FASTER FORWARD SPEED. HOWEVER...THIS IS A SIGNIFICANT CHANGE FROM THE PREVIOUS MODELS RUNS...AND THERE IS CONSIDERABLE SPREAD IN BOTH THE DIRECTION AND SPEED OF MOTION. THUS...THE NEW FORECAST FOR THOSE TIMES IS ONLY SLIGHTLY FASTER THAN THE PREVIOUS FORECAST...AND CONSIDERABLY SLOWER THAN THE CURRENT GUIDANCE. THERE IS LITTLE CHANGE TO THE INTENSITY FORECAST PHILOSOPHY FROM THE LAST SEVERAL ADVISORIES. BERTHA SHOULD MAINTAIN ITS INTENSITY FOR THE FIRST 24-36 HR WHILE UNDER AN UPPER-LEVEL ANTICYCLONE AND OVER WARM SURFACE TEMPERATURES. BY 36 HR...THE HURRICANE SHOULD BEGIN TO WEAKEN AS IT REACHES COOLER WATERS. THEN...BY 72 HR THE VERTICAL WIND SHEAR IS FORECAST TO INCREASE...WHICH SHOULD INCREASE THE WEAKENING RATE. THE INTENSITY FORECAST IS IDENTICAL TO THE LAST ADVISORY THROUGH 48 HR...THEN SHOWS MORE WEAKENING DUE TO THE EXPECTED SHEAR. A TROPICAL STORM WARNING WILL LIKELY BE ISSUED FOR BERMUDA LATER THIS MORNING. FORECAST POSITIONS AND MAX WINDS INITIAL 12/0900Z 29.7N 62.5W 80 KT 12HR VT 12/1800Z 30.1N 62.6W 80 KT 24HR VT 13/0600Z 30.7N 62.6W 80 KT 36HR VT 13/1800Z 31.3N 62.6W 75 KT 48HR VT 14/0600Z 31.9N 62.6W 70 KT 72HR VT 15/0600Z 33.5N 62.5W 60 KT 96HR VT 16/0600Z 35.0N 61.5W 50 KT 120HR VT 17/0600Z 36.5N 59.5W 50 KT $$ FORECASTER BEVEN |
