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| #200890 (Received by flhurricane at: 11:08 PM 13.Jul.2008) TCDAT2 TROPICAL STORM BERTHA DISCUSSION NUMBER 44 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022008 1100 PM EDT SUN JUL 13 2008 IT APPEARS THAT BERTHA IS TAPPING LIGHTLY ON THE ACCELERATOR...WITH AN INITIAL MOTION ESTIMATE OF 335/3. MOST OF THE MODELS FORECAST A GRADUAL INCREASE IN BERTHA'S FORWARD SPEED WITH A SUBTLE TURN TO THE RIGHT DURING THE NEXT COUPLE OF DAYS...AROUND A WEAK MID-LEVEL HIGH CURRENTLY JUST EAST OF THE STORM. BY THAT TIME THE MODELS FORECAST BERTHA TO BE NORTH OF THE RIDGE...AND IN BETWEEN A MID-LATITUDE TROUGH NEAR THE NORTHEAST U.S. COAST AND A CUTOFF LOW OVER THE CENTRAL NORTH ATLANTIC. BERTHA AND THE CUTOFF LOW ARE THEN FORECAST TO INTERACT WITH ONE ANOTHER IN A POTENTIALLY COMPLEX MANNER ON DAYS 3 THROUGH 5...ALTHOUGH A GENERALLY EASTWARD MOTION WITHIN THE MID-LATITUDE WESTERLIES IS IMPLIED BY THE MODEL CONSENSUS. THE UNUSUAL UNDULATIONS IN THE OFFICIAL TRACK BEYOND 48 HOURS ARE SUPPORTED BY ALL OF THE DYNAMICAL MODELS...BUT THE DIPS AND TURNS IN THE MODEL TRACKS ARE A BIT MORE EXTREME THAN SHOWN IN THE OFFICIAL FORECAST. THERE IS ALSO GREAT DISAGREEMENT IN THE GUIDANCE ON THE FORWARD SPEED OF BERTHA DURING THAT TIME FRAME...BUT THE FIVE-DAY CONSENSUS POINT IS NOT FAR FROM THAT IN THE PREVIOUS ADVISORY...SO ON BALANCE THE NEW TRACK IS NOT THAT MUCH OF A CHANGE. I HAVE NO SOLID REASON TO ALTER THE INITIAL INTENSITY OF 55 KT...AS THE SUBJECTIVE DVORAK ESTIMATES HAVE NOT CHANGED MUCH...AND A QUIKSCAT OVERPASS AROUND 23Z ONLY CAPTURED THE WESTERN HALF OF THE CIRCULATION. CLOUD TOPS OF THE OUTER BANDS HAVE WARMED DURING THE PAST FEW HOURS...BUT IF ANYTHING THE CONVECTION NEAR THE CENTER HAS INCREASED EVER SO SLIGHTLY. A CONSENSUS OF THE VARIOUS INTENSITY MODELS DOES NOT SUGGEST MUCH CHANGE IN BERTHA'S STRENGTH DURING THE NEXT SEVERAL DAYS AS IT PASSES OVER GRADUALLY COOLER SEA-SURFACE TEMPERATURES. THE NEW OFFICIAL FORECAST HOLDS ON TO THE CURRENT INTENSITY THROUGH 36 HOURS AND ONLY SHOWS A SLIGHTLY WEAKER SYSTEM BEYOND THAT TIME. THIS FORECAST IS VERY CLOSE TO THE SHIPS AND LGEM...BUT STILL BELOW THE GFDL AND HWRF THAT FORECAST BERTHA TO AGAIN BECOME A HURRICANE. WHILE THAT POSSIBILITY CANNOT BE RULED OUT...IT APPEARS TO BE THE LESS LIKELY OPTION...ESPECIALLY GIVEN THE CONVOLUTED STATE OF BERTHA'S INNER CORE. FORECAST POSITIONS AND MAX WINDS INITIAL 14/0300Z 30.5N 63.1W 55 KT 12HR VT 14/1200Z 31.5N 63.5W 55 KT 24HR VT 15/0000Z 33.0N 63.6W 55 KT 36HR VT 15/1200Z 34.6N 63.1W 55 KT 48HR VT 16/0000Z 35.8N 62.0W 50 KT 72HR VT 17/0000Z 35.5N 59.5W 50 KT 96HR VT 18/0000Z 34.5N 56.5W 50 KT 120HR VT 19/0000Z 35.5N 53.0W 50 KT $$ FORECASTER KNABB |
