[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 180901
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


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