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| #9108 (Received by flhurricane at: 5:14 AM 18.Sep.2004) TCDAT1 TROPICAL STORM JEANNE DISCUSSION NUMBER 19 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 AM EDT SAT SEP 18 2004 THERE CONTINUE TO BE DIFFERENCES AMONG THE GLOBAL MODELS ON THE EVOLUTION OF THE MID-LEVEL REMNANTS OF IVAN. THE 00Z GFS BREAKS OFF A SIGNIFICANT PIECE OF IVAN AND TAKES IT SOUTHWESTWARD JUST OFF THE CAROLINAS IN ABOUT TWO DAYS. IN THIS SCENARIO...JEANNE IS LIFTED NORTHWARD AROUND THE EAST SIDE OF THESE REMNANTS AND THEN NORTHEASTWARD UNTIL LATE IN THE FORECAST PERIOD. THE 00Z NOGAPS SCENARIO IS FOR IVAN'S MID-LEVEL CIRCULATION TO WEAKEN AND/OR TO CONTINUE NORTHEASTWARD...RESULTING IN JEANNE GETTING TRAPPED MORE QUICKLY UNDER THE STRONG HIGH FORECAST TO MOVE THROUGH THE GREAT LAKES IN 3-5 DAYS. THE UKMET TRACK IS EVEN MORE EMPHATIC ABOUT A CAPTURE. YET ONE THING ALL THESE MODELS HAVE IN COMMON IS AN IMMEDIATE NORTHWARD MOTION OF A VERTICALLY WELL-CONNECTED TROPICAL CYCLONE. SATELLITE IMAGERY SHOWS A EXPOSED CIRCULATION WITH ONLY A LITTLE BIT OF CONVECTION IN THE NORTHEAST QUADRANT...NOT ENOUGH TO MAKE ONE THINK THAT JEANNE HAS MUCH VERTICAL COHERENCE. YET...THE LAST TWO RECONNAISSANCE FIXES DID GIVE AN ALMOST DUE NORTHWARD MOTION. WHETHER THE MODELS ARE SEEING SOMETHING I DON'T SEE...OR WHETHER THE CENTER IS ONLY BEING DRAGGED TEMPORARILY TO THE RIGHT BY THE CONVECTION IS NOT YET CLEAR. THE OFFICIAL FORECAST THINKING IS THAT JEANNE IS NOT QUITE READY TO GO AS FAST TO THE NORTH AS THE GLOBAL MODELS ARE FORECASTING...BUT RATHER IS IN BETTER AGREEMENT WITH THE SIMPLER BAM STEERING MODELS...AT LEAST FOR THE FIRST 48 HOURS OR SO. IF JEANNE DOES IN FACT TURN NORTH ONLY SLOWLY...IT WOULD MOST LIKELY BE FORCED BACK TO THE WEST BY THE END OF THE FORECAST PERIOD. GIVEN ALL THE ABOVE...IT IS PROBABLY OBVIOUS THAT THIS IS NOT A HIGH CONFIDENCE FORECAST. RECONNAISSANCE DATA SHOW 55 KT OF WIND AT A FLIGHT LEVEL OF 1500 FT. IF JEANNE WERE A MORE CONVECTIVE STORM THAT WOULD CORRESPOND TO 45 KT AT THE SURFACE...BUT GIVEN THE PRESENT STRUCTURE I WILL HOLD THE INITIAL INTENSITY AT 40 KT. JEANNE IS CURRENTLY JUST TO THE SOUTHEAST OF AN UPPER-LEVEL SHEAR AXIS...RESULTING IN MODERATE WESTERLY SHEAR OVER THE LOW-LEVEL CIRCULATION. SHOULD JEANNE TURN MORE NORTHWARD IT COULD FIND ITSELF UNDER A MORE FAVORABLE UPPER PATTERN IN A COUPLE OF DAYS...WHILE A MORE WESTWARD TRACK WOULD KEEP JEANNE UNDER UNFAVORABLE SOUTHWESTERLY SHEAR. THUS IT WOULD SEEM UNLIKELY THAT A STRONG SYSTEM COULD MAKE ANY SIGNIFICANT WEST-NORTHWESTWARD PROGRESS. IN FACT...A NOT UNREASONABLE ALTERNATIVE TO THE FORECAST BELOW WOULD BE FOR THE LOW-LEVEL CENTER TO CONTINUE TO THE WEST-NORTHWEST AND DISSIPATE...AS DEBBY DID IN THIS AREA FOUR YEARS AGO. FORECASTER FRANKLIN FORECAST POSITIONS AND MAX WINDS INITIAL 18/0900Z 20.7N 72.6W 40 KT 12HR VT 18/1800Z 21.4N 73.0W 40 KT 24HR VT 19/0600Z 22.4N 73.4W 45 KT 36HR VT 19/1800Z 23.8N 73.7W 50 KT 48HR VT 20/0600Z 25.5N 73.7W 50 KT 72HR VT 21/0600Z 27.5N 73.5W 50 KT 96HR VT 22/0600Z 28.0N 73.5W 50 KT 120HR VT 23/0600Z 28.5N 74.5W 50 KT |
