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| #200529 (Received by flhurricane at: 11:08 PM 11.Jul.2008) TCDAT2 HURRICANE BERTHA DISCUSSION NUMBER 36 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022008 1100 PM EDT FRI JUL 11 2008 THE GEOSTATIONARY SATELLITE APPEARANCE OF BERTHA HAS NOT CHANGED THAT MUCH SINCE THE RECONNAISSANCE AIRCRAFT DEPARTED SEVERAL HOURS AGO...AND THE SUBJECTIVE DVORAK ESTIMATES ARE ABOUT THE SAME...SO THE ADVISORY INTENSITY REMAINS 80 KT. BOTH INFRARED AND MICROWAVE IMAGERY SUGGEST THERE IS STILL SOMETHING OF AN INNER EYEWALL THAT REFUSES TO COMPLETELY GO AWAY...WHILE THE OUTER EYEWALL PERSISTS AS A CLOSED RING AT A SLIGHTLY SMALLER RADIUS THAN 24 HOURS AGO. ALL OF THAT MEANS THAT THE WELL-ADVERTISED EYEWALL REPLACEMENT CYCLE IS NOT EXACTLY PROCEEDING AT A BLISTERING PACE...AND I AM REALLY NOT SURE HOW THE INNER CORE STRUCTURE WILL EVOLVE DURING THE NEXT 24 HOURS OR SO. PERSISTENCE MIGHT BE A GOOD GUIDE...SO A VERY SLOW CHANGE IN BERTHA'S STRUCTURE WILL BE THE ASSUMPTION DRIVING THE FLAT INTENSITY FORECAST THROUGH 24 HOURS. VERY GRADUAL WEAKENING IS FORECAST THEREAFTER...IN ACCORDANCE WITH A CONSENSUS OF OUR PRIMARY INTENSITY MODELS...AS BERTHA TAKES ITS TIME MOVING TOWARD COOLER WATERS. THE NEW OFFICIAL INTENSITY FORECAST IS ALMOST AN EXACT COPY OF THE PREVIOUS ONE. BERTHA IS CAUGHT IN A VERY WEAK STEERING REGIME AS IT CONTINUES MOVING...BARELY...AT 335/4. THE DYNAMICAL MODELS DO NOT OFFER MUCH PROGNOSTIC EVIDENCE THAT A MID-LATITUDE TROUGH WITH SUFFICIENT AMPLITUDE WILL BE ABLE TO GET BERTHA MOVING MUCH FASTER WITHIN THE FIVE-DAY FORECAST PERIOD. THE SHORTWAVE TROUGH CURRENTLY ALONG THE U.S. NORTHEAST COAST WILL ALMOST CERTAINLY BYPASS BERTHA WELL TO THE NORTH...AND NONE OF THE MODELS FORECAST BERTHA TO ACCELERATE AHEAD OF THE NEXT TROUGH WITHIN FIVE DAYS...ALTHOUGH THAT TROUGH LOOKS TO BE STRONGER AND MIGHT TRULY PICK UP BERTHA BEYOND THAT TIME. IN BETWEEN THOSE TWO TROUGHS...THE MODELS DISAGREE ON HOW MUCH OF A RIDGE MIGHT FORM NORTH OF BERTHA...AND SOME OF THEM FORECAST BERTHA TO STALL WITHIN THE NEXT DAY OR TWO. IN ADDITION...MOST OF THE MODELS SHOW AT LEAST SOME SOUTHWARD COMPONENT OF MOTION ON DAY 5...IN RESPONSE TO A CUTOFF LOW FORECAST TO BE NOT FAR NORTHEAST OF BERTHA BY THAT TIME. THE RESULT OF THE COMPLICATED SET OF INDIVIDUAL MODEL TRACKS IS A CONSENSUS THAT LEADS ME TO SLOW DOWN THE OFFICIAL FORECAST JUST SLIGHTLY...ALSO WITH A NUDGE TO THE WEST...ALONG A TRACK SIMILAR TO THE PREVIOUS ADVISORY THAT SIMPLY BENDS BERTHA'S MOTION GRADUALLY TO THE RIGHT... AT A SPEED OF ABOUT 3 KT THROUGHOUT THE FIVE-DAY FORECAST. SOME ERRATIC MOTION AT SOME POINT ALONG THE WAY WOULD NOT BE SURPRISING. THE PROBABILITY OF WINDS OF TROPICAL STORM FORCE OCCURRING IN BERMUDA WITHIN THE NEXT FIVE DAYS...AS CONVEYED IN THE WIND SPEED PROBABILITY PRODUCT INCLUDED IN EACH ADVISORY PACKAGE...HAS BEEN GRADUALLY RISING DURING THE PAST COUPLE OF DAYS...AND HAS NOW REACHED 58%. FORECAST POSITIONS AND MAX WINDS INITIAL 12/0300Z 29.4N 62.4W 80 KT 12HR VT 12/1200Z 30.0N 62.6W 80 KT 24HR VT 13/0000Z 30.6N 62.6W 80 KT 36HR VT 13/1200Z 31.2N 62.5W 75 KT 48HR VT 14/0000Z 31.7N 62.4W 70 KT 72HR VT 15/0000Z 33.0N 62.0W 65 KT 96HR VT 16/0000Z 34.0N 61.5W 60 KT 120HR VT 17/0000Z 35.0N 60.5W 60 KT $$ FORECASTER KNABB |
