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| #5654 (Received by flhurricane at: 10:58 PM 18.Aug.2004) TCDAT4 TROPICAL STORM DANIELLE DISCUSSION NUMBER 23 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 PM EDT WED AUG 18 2004 DANIELLE SHOWS A SHEARED CLOUD PATTERN THIS EVENING...WITH THE LOW LEVEL CENTER EXPOSED TO THE SOUTHWEST OF AN AREA OF PERSISTENT CONVECTION. THE INITIAL INTENSITY OF 40 KT IS BASED ON A QUIKSCAT OVERPASS AT 18/2036Z WITH UNCONTAMINATED 40 KT WINDS...AND A COMBINATION OF SATELLITE INTENSITY ESTIMATES. DANIELLE HAS TURNED RIGHT DURING THE PAST 6 HR AND THE INITIAL MOTION IS NOW 055/9...AND THAT MAY BE GENEROUS ON THE SPEED. THE STORM IS EMBEDDED IN A LOW/MID LEVEL SUBTROPICAL RIDGE...WITH A MID/UPPER-LEVEL SHORTWAVE RIDGE PASSING TO THE NORTH OF THE STORM AND A STRONG MID/UPPER-LEVEL LOW TO THE WEST NEAR 33N45W. LARGE- SCALE MODELS SUGGEST A LOW AND ASSOCIATED UPPER-LEVEL SHORTWAVE TROUGH WILL PASS NORTH OF DANIELLE DURING THE NEXT 72 HR...FOLLOWED BY A DEEP LAYER RIDGE BUILDING NEAR THE AZORES. TRACK GUIDANCE RESPONDS TO THIS WITH SOME DIVERGENCE. THE GFS LOSES DANIELLE QUICKLY...WHILE THE GFDL STALLS THE CYCLONE FOR 72 HR FOLLOWED BY A NORTH-NORTHWESTWARD MOTION. THE UKMET/NOGAPS CALL FOR A SLOW NORTHEASTWARD MOTION FOR 72-96 HR...WITH THE NOGAPS TURNING NORTHWESTWARD AFTER THAT. THE OFFICIAL FORECAST FOLLOWS THE UKMET/NOGAPS FOR 96 HR...BUT SHOWS LESS OF A TURN THAN THE NOGAPS AT 120 HR. THE NEW TRACK IS ABOUT A DEGREE SOUTH OF AND SLOWER THAN THE PREVIOUS TRACK. DANIELLE SHOULD STAY OVER 25-26C SEA SURFACE TEMPERATURES THROUGH 72 HR...SO THE BIGGEST INTENSITY QUESTION IS HOW MUCH SHEAR WILL OCCUR. THE MODELS AGAIN DIVERGE ON THE UPPER-LEVEL WIND PATTERN. THE GFS/CANADIAN MODELS TAKE THE UPPER-LEVEL LOW WEST OF DANIELLE AND MOVE IT BODILY EASTWARD ACROSS THE CYCLONE...WHICH WOULD LIKELY DESTROY DANIELLE. THE UKMET/NOGAPS ALSO MOVE THE LOW EASTWARD BUT WEAKENING IT RAPIDLY WHILE DOING SO...WHICH COULD LEAVE DANIELLE IN A LOWER SHEAR ENVIRONMENT AND ALLOW IT TO MAINTAIN SOME STRENGTH. THE INTENSITY FORECAST COMPROMISES BETWEEN THESE TWO SOLUTIONS... CALLING FOR A GRADUAL WEAKENING IN BEST AGREEMENT WITH THE GFDL. BY 72 HR...A COLD FRONT ASSOCIATED WITH THE LOW TO THE NORTH SHOULD REACH DANIELLE AND CAUSE EXTRATROPICAL TRANSITION. FORECASTER BEVEN FORECAST POSITIONS AND MAX WINDS INITIAL 19/0300Z 29.6N 37.5W 40 KT 12HR VT 19/1200Z 30.2N 36.7W 35 KT 24HR VT 20/0000Z 31.2N 35.8W 30 KT 36HR VT 20/1200Z 32.3N 35.0W 25 KT 48HR VT 21/0000Z 33.1N 33.9W 25 KT 72HR VT 22/0000Z 34.5N 31.0W 25 KT...EXTRATROPICAL 96HR VT 23/0000Z 36.0N 28.0W 25 KT...EXTRATROPICAL 120HR VT 24/0000Z 38.0N 27.0W 25 KT...EXTRATROPICAL |
