385
WTPZ42 KNHC 290832
TCDEP2
TROPICAL STORM JOHN DISCUSSION NUMBER 4
NATIONAL WEATHER SERVICE MIAMI FL
2 AM PDT TUE AUG 29 2000
JOHN IS PRESENTING ABOUT THE SAME APPEARANCE ON INFRARED IMAGERY NOW
AS IT WAS SIX HOURS AGO...AND THE DVORAK INTENSITY ESTIMATES FROM
TAFB AND SAB REMAIN AT 55 KT. ALTHOUGH OUTFLOW HAS BEEN EXPANDING
TO THE WEST...THERE DOES APPEAR TO BE SOME WESTERLY FLOW APPROACHING
THE CYCLONE AND UNDERCUTTING THIS OUTFLOW. MOST OF THE DEEP
CONVECTION IS ON THE NORTH SIDE OF THE CENTER...WHICH WAS DETERMINED
FROM AN SSMI PASS OBTAINED FROM THE NRL/MONTEREY TROPICAL CYCLONE
WEB PAGE. THIS PASS ALSO SUGGESTS A PARTIAL CENTRAL RING OF HEAVIER
RAIN THAT COULD BE THE BEGINNINGS OF AN EYEWALL.
NONE OF THE GUIDANCE SUGGESTS SIGNIFICANT STRENGTHENING. SHIPS
KEEPS THE SYSTEM ROUGHLY STEADY STATE FOR 36 HOURS AND THEN SLOWLY
WEAKENS IT. NEITHER THE UKMET NOR THE GFDL FORECAST JOHN TO BECOME
A HURRICANE...BUT GIVEN THE GOOD INNER CORE ORGANIZATION THIS COULD
STILL HAPPEN AND I HAVE BACKED OFF ONLY SLIGHTLY FROM THE PREVIOUS
INTENSITY FORECAST. THE SPREAD OF THE BAM TRACK MODELS SUGGESTS
VERY HIGH SHEAR LATE IN THE FORECAST PERIOD AND THE OFFICIAL
FORECAST WEAKENS THE CYCLONE AFTER 36 HOURS.
THE TRACK FORECAST GUIDANCE IS HIGHLY DIVERGENT. THE LBAR...DEEP
BAM...AND THE STATISTICAL MODEL TAKE JOHN ULTIMATELY TO THE
NORTHEAST. THE REST OF THE GUIDANCE GENERALLY BENDS THE TRACK
SMARTLY TO THE WEST AND THEN SOUTH OF WEST. GIVEN THIS SPLIT...THE
OFFICIAL FORECAST GOES SLOW...BUT LEANS TOWARD THE LATTER SOLUTION
AND IS NOT FAR FROM THE PREVIOUS FORECAST TRACK.
RADII HAVE BEEN ADJUSTED OUTWARD IN THE SOUTHEAST QUADRANT BASED ON
PERSISTENT SHIP REPORTS OF HIGH WINDS AND SEAS.
FORECASTER FRANKLIN
FORECAST POSITIONS AND MAX WINDS
INITIAL 29/0900Z 16.1N 139.0W 55 KTS
12HR VT 29/1800Z 16.4N 139.5W 65 KTS
24HR VT 30/0600Z 16.7N 140.1W 65 KTS
36HR VT 30/1800Z 16.9N 140.9W 65 KTS
48HR VT 31/0600Z 17.0N 141.7W 60 KTS
72HR VT 01/0600Z 17.0N 143.0W 50 KTS
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