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| #200354 (Received by flhurricane at: 11:08 PM 10.Jul.2008) TCDAT2 HURRICANE BERTHA DISCUSSION NUMBER 32 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022008 1100 PM EDT THU JUL 10 2008 A SERIES OF MICROWAVE OVERPASSES THROUGHOUT THE DAY INDICATE THAT THE INNER EYEWALL HAS BEEN SLOWLY DETERIORATING...WHILE A NEW OUTER EYEWALL HAS BEEN TAKING SHAPE. THE MOST RECENT IMAGE...FROM SSMIS AT 2319Z...DEPICTS THE OUTER EYEWALL AS A COMPLETELY CLOSED RING AT A RADIUS OF ABOUT 60 N MI...WITH BARELY HALF OF THE INNER EYEWALL REMAINING. TRENDS IN GEOSTATIONARY INFRARED IMAGERY REFLECT THE EVOLVING STRUCTURE...AS THE EYE HAS JUST ABOUT DISAPPEARED WHILE CLOUD TOPS HAVE BEEN COOLING ABOVE THE OUTER RING SEEN IN THE MICROWAVE. IN ADDITION...A QUIKSCAT PASS BACK AT 23Z DEPICTED A SECONDARY WIND MAXIMUM IN THE OUTER EYEWALL. DVORAK INTENSITY ESTIMATES AT 00Z WERE ALL 75 KT...BUT IT IS HARD TO ESTIMATE EVEN VERY SHORT-TERM INTENSITY CHANGES GIVEN THE ONGOING STRUCTURAL CHANGES...EVEN THOUGH THE OCEAN AND ATMOSPHERIC ENVIRONMENTS ARE NOT PROHIBITIVE FOR STRENGTHENING. IT IS POSSIBLE THAT BERTHA WILL WEAKEN SOME UPON THE FINAL DEMISE OF THE INNER EYEWALL...AND IT IS ALSO POSSIBLE THAT THE NEW OUTER EYEWALL WILL EVENTUALLY CONTRACT AND BE ACCOMPANIED BY SOME STRENGTHENING...BUT I AM NOT GOING TO TRY TO EXPLICITLY FORECAST SUCH CHANGES. THE MOST PRUDENT APPROACH...WHICH IS ALSO SUPPORTED BY THE OBJECTIVE GUIDANCE...IS TO KEEP THE INTENSITY LEVEL FOR THE NEXT COUPLE OF DAYS...FOLLOWED BY GRADUAL WEAKENING AS THE WIND SHEAR POTENTIALLY INCREASES AND BERTHA PASSES OVER GRADUALLY COOLER SEA-SURFACE TEMPERATURES. THE NEW INTENSITY FORECAST HAS JUST A SLIGHTLY LOWER PEAK INTENSITY THAN THE PREVIOUS ADVISORY. BERTHA APPEARS TO BE GRADUALLY SLOWING DOWN...AND THE INITIAL MOTION ESTIMATE IS NOW 315/7. THE FORECAST AND ITS SUPPORTING REASONING HAVE NOT REALLY CHANGED FOR THE FIRST 48 HOURS OR SO...INCLUDING A VERY SLOW FORWARD MOTION IN A COUPLE OF DAYS NEAR BERMUDA. BEYOND THAT TIME...ESSENTIALLY ALL OF THE MODELS HAVE SHIFTED TO THE EAST AND FORECAST A FASTER MOTION AT 4-5 DAYS...THIS TIME FORECASTING BERTHA TO BE PULLED NORTHWARD A LITTLE SOONER BY A TROUGH ALONG THE U.S. EAST COAST BY THEN...WITH SLIGHTLY LESS RIDGING TO THE NORTH TO BLOCK BERTHA'S POLEWARD PROGRESS. THE NEW OFFICIAL TRACK FORECAST DOES NOT COMPLETELY BUY INTO THIS MUCH OF A SHIFT IN THE MODELS...BUT IT IS ADJUSTED EASTWARD AND MOST OF THE WAY TOWARD THE CONSENSUS. SINCE THIS NEW TRACK STILL DOES NOT FORECAST BERTHA TO BE GOING ANY FASTER THAN ABOUT 5-7 KT AT THE END OF THE FIVE-DAY PERIOD...THIS ADJUSTMENT DOES NOT REPRESENT A HUGE CHANGE IN WHERE WE EXPECT BERTHA TO BE IN FIVE DAYS. THE LATEST WIND SPEED PROBABILITY PRODUCT ACCOMPANYING THIS ADVISORY PACKAGE INDICATES THAT...GIVEN UNCERTAINTIES IN THE FORECASTS OF BERTHA'S TRACK...INTENSITY...AND SIZE...THERE ROUGHLY A 50% CHANCE THAT WINDS OF TROPICAL STORM FORCE WILL AFFECT BERMUDA DURING THE NEXT FIVE DAYS. FORECAST POSITIONS AND MAX WINDS INITIAL 11/0300Z 27.7N 61.2W 75 KT 12HR VT 11/1200Z 28.4N 61.9W 75 KT 24HR VT 12/0000Z 29.5N 62.6W 75 KT 36HR VT 12/1200Z 30.4N 62.6W 75 KT 48HR VT 13/0000Z 31.1N 62.3W 70 KT 72HR VT 14/0000Z 32.5N 61.5W 65 KT 96HR VT 15/0000Z 34.5N 60.5W 60 KT 120HR VT 16/0000Z 37.0N 59.0W 55 KT $$ FORECASTER KNABB |
