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| #211634 (Received by flhurricane at: 5:00 AM 30.Aug.2008) TCDAT3 TROPICAL STORM HANNA DISCUSSION NUMBER 9 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082008 500 AM EDT SAT AUG 30 2008 THERE HAS BEEN NO SIGNIFICANT CHANGE IN THE CLOUD PATTERN OF HANNA. THE CENTER CONTINUES TO RUN AWAY FROM THE CONVECTION AND NEW THUNDERSTORM ACTIVITY REDEVELOPS OVER IT. THIS MEANS THAT THE SHEAR HAS NOT RELAXED YET. A NOAA BUOY...41043...HAS BEEN EXTREMELY USEFUL IN TRACKING THE CYCLONE. IT HAS DEPICTED THE WELL-DEFINED SURFACE CIRCULATION ASSOCIATED WITH HANNA AND HAS RECENTLY REPORTED A MINIMUM PRESSURE OF NEAR 1002 MB. AS LONG AS THE MODERATE SHEAR PREVAILS...CAUSED BY THE RESILIENT UPPER-LOW...HANNA MOST LIKELY WILL NOT STRENGTHEN. THE OFFICIAL FORECAST CALLS FOR NO CHANGE IN INTENSITY DURING THE NEXT 12 HOURS OR SO. GLOBAL MODELS INSIST ON WEAKENING THE UPPER-LOW...CREATING A MORE FAVORABLE ENVIRONMENT FOR HANNA TO STRENGTHEN IN THE PERIOD BETWEEN 12 AND 48 HOURS. THEREAFTER...THE SHEAR IS FORECAST TO INCREASE AND THIS IS REFLECTED IN THE OFFICIAL FORECAST BY SHOWING SOME SLIGHT WEAKENING. MOST OF THE MODELS CONTINUE TO INTENSIFY HANNA...SOME OF THEM QUITE SIGNIFICANTLY...DESPITE THE SHEAR. I DO NOT HAVE AN EXPLANATION FOR IT. THE CENTER IS VERY DIFFICULT TO LOCATE ON IR IMAGES BUT SATELLITE FIXES AND DATA FROM THE NOAA BUOY SUGGEST THAT HANNA HAS BEEN MOVING WESTWARD OR 280 DEGREES AT 10 KNOTS. FOR ABOUT 12 TO 24 HOURS...A WEST-NORTHWEST MOTION AROUND THE UPPER-LOW IS ANTICIPATED. THEREAFTER...A STRONG SUBTROPICAL HIGH WHICH IS FORECAST TO BUILD TO THE NORTH OF HANNA WILL THEN PROVIDE THE DOMINANT STEERING FLOW. THIS SHOULD FORCE THE CYCLONE ON A WESTWARD AND THEN AN EVEN SLOWER WEST-SOUTHWESTWARD TRACK. I TRIED VERY HARD NOT TO FORECAST THE WEST-SOUTHWEST TURN SINCE THIS IS NOT A VERY COMMON TROPICAL CYCLONE TRACK BUT RELIABLE DYNAMICAL GUIDANCE HAS FORCED ME TO DO SO. THE OFFICIAL FORECAST IS PRACTICALLY ON TOP OF THE MODEL CONSENSUS. I ALWAYS WONDERED HOW TODAY'S SOPHISTICATED DYNAMICAL MODELS WOULD HAVE FORECAST HURRICANE BETSY BACK IN 1965. THIS HURRICANE MOVED SOUTHWESTWARD OVER THE BAHAMAS. FORECAST POSITIONS AND MAX WINDS INITIAL 30/0900Z 21.9N 66.3W 45 KT 12HR VT 30/1800Z 22.6N 68.0W 45 KT 24HR VT 31/0600Z 23.3N 70.0W 50 KT 36HR VT 31/1800Z 23.5N 71.5W 60 KT 48HR VT 01/0600Z 23.5N 72.5W 65 KT 72HR VT 02/0600Z 23.5N 74.0W 65 KT 96HR VT 03/0600Z 23.0N 75.5W 60 KT 120HR VT 04/0600Z 22.5N 77.0W 55 KT $$ FORECASTER AVILA |
