Flhurricane.com - Central Florida Hurricane Center - Tracking Storms since 1995Hurricanes Without the Hype! Since 1995
The Atlantic is quiet
|
Show Selection: |
| #213183 (Received by flhurricane at: 11:04 AM 03.Sep.2008) TCDAT3 TROPICAL STORM HANNA DISCUSSION NUMBER 27 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082008 1100 AM EDT WED SEP 03 2008 THERE HAVE BEEN SOME STRUCTURAL CHANGES WITH HANNA TODAY AS IT INTERACTS WITH THE UPPER-LEVEL LOW MOVING THROUGH THE NORTHWESTERN BAHAMAS. THE WIND FIELD HAS EXPANDED IN THE NORTHERN SEMICIRCLE AND THE LOW-LEVEL CIRCULATION CENTER HAS BECOME LESS WELL DEFINED. VISIBLE IMAGERY SUGGESTS MULTIPLE LOW-LEVEL SWIRLS COMING OUT OF THE DEEP CONVECTION TO THE NORTH OF A MEAN CENTER...AND THE SYSTEM'S CONVECTIVE BANDS ARE WELL REMOVED FROM THE CORE. THE RECONNAISSANCE MISSION THAT ENDED AROUND 12Z REPORTED SOME SFMR WINDS OF UP TO 45 KT ABOUT 70 NM FROM THE CENTER...AND THE INITIAL INTENSITY ESTIMATE REMAINS 50 KT. BECAUSE THE CENTER IS NOT WELL DEFINED...THE INTIAL MOTION IS HARD TO GAUGE. MY BEST ESTIMATE IS 360/5...AND THIS COULD BE THE START OF THE EXPECTED NORTHWESTWARD TURN. THE STEERING FLOW SHOULD BECOME BETTER DEFINED OVER THE NEXT 24-48 HOURS AS THE UPPER LOW MOVES WEST-SOUTHWESTWARD AND MID-LEVEL RIDGING BUILDS IN BEHIND THE LARGE DEEP-LAYER LOW OFF THE UPPER U.S. EAST COAST. MODEL GUIDANCE RESPONDS TO THIS PATTERN WITH A NORTHWESTWARD ACCELERATION WITH A RECURVATURE AROUND THE MID-LEVEL RIDGE IN ABOUT THREE DAYS. THE GUIDANCE HAS BEEN TOO FAST WITH THIS SCENARIO OVER THE PAST COUPLE OF DAYS...AND GIVEN THE POOR CORE STRUCTURE OF HANNA I AM INCLINED TO THINK THAT SUBSEQUENT INTERACTION WITH THE UPPER STEERING MAY BE A LITTLE OVERDONE...AT LEAST INITIALLY. THE OFFICIAL FORECAST IS IN BEST AGREEMENT WITH THE ECMWF AND UKMET IN TERMS OF SPEED...WITH THE GFS/HWRF/GFDL SHOWING A MORE VERTICAL SYSTEM MOVING MORE RAPIDLY. THE GUIDANCE HAS ALSO BEEN TRENDING EASTWARD OVER THE PAST FEW CYCLES...AND I HAVE SHIFTED THE TRACK SLIGHTLY IN THAT DIRECTION. WESTERLY SHEAR AND DRY AIR ASSOCIATED WITH THE UPPER LOW WILL INHIBIT DEVELOPMENT IN THE SHORT TERM BUT SHOULD DIMINISH OVER THE NEXT COUPLE OF DAYS...TO BE REPLACED WITH MODERATE SOUTHEASTERLY SHEAR. THIS PATTERN WOULD PERMIT SOME RE-INTENSIFICATION...BUT HANNA WILL NEED TO RECREATE AN INNER CORE IN ORDER TO INTENSIFY SUBSTANTIALLY. THE AVAILABLE GUIDANCE STILL BRINGS HANNA TO MINIMAL HURRICANE INTENSITY AND THE OFFICIAL FORECAST IS JUST ABOVE THIS GUIDANCE. FORECAST POSITIONS AND MAX WINDS INITIAL 03/1500Z 20.6N 71.8W 50 KT 12HR VT 04/0000Z 21.5N 72.0W 50 KT 24HR VT 04/1200Z 23.4N 73.3W 55 KT 36HR VT 05/0000Z 25.2N 75.2W 60 KT 48HR VT 05/1200Z 27.3N 77.1W 65 KT 72HR VT 06/1200Z 33.0N 79.0W 70 KT 96HR VT 07/1200Z 42.0N 71.0W 35 KT...INLAND EXTRATROPICAL 120HR VT 08/1200Z 47.0N 60.0W 35 KT...EXTRATROPICAL $$ FORECASTER FRANKLIN |
