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TROPICAL STORM JOHN DISCUSSION NUMBER   7
NATIONAL WEATHER SERVICE MIAMI FL
8 PM PDT TUE AUG 29 2000

DURING THE PAST 6 HOURS...STRONG CONVECTION HAS REDEVELOPED NEAR THE
CENTER OF CIRCULATION.  THE INITIAL INTENSITY OF 55 KT IS BASED A
DVORAK SATELLITE ESTIMATE OF 55 KT FROM BOTH TAFB AND SAB.  OUTFLOW
REMAINS GOOD IN THE NORTH SEMICIRCLE AND FAIR BUT IMPROVING
ELSEWHERE...AND A SMALL CDO APPEARS TO BE REDEVELOPING.
 
CURRENT MOTION ESTIMATE IS 295/6.  JOHN HAS BEEN BUCKING THE UPPER-
LEVEL SOUTHWESTERLY SHEAR WHICH HAS BEEN IMPEDING ITS WESTWARD
MOTION.  THE LOW- AND MID-LEVEL RIDGE TO THE NORTH IS STRONG ENOUGH
TO KEEP THE CYCLONE ON A GENERAL WESTWARD TRACK THROUGH 36
HOURS...AFTER WHICH THE STEERING FLOW COLLAPSES AS AN UPPER-LEVEL
TROUGH TO THE NORTHEAST RETROGRADES TO THE SOUTHWEST.  ALL OF THE
MODELS AGREE ON JOHN SLOWING DOWN TO A CRAWL IN 36 HOURS...BUT THEN
SPLIT INTO TWO CAMPS EITHER TAKING THE SYSTEM SLOWLY NORTHEAST OR
SLOWLY SOUTHEAST.  WE HAVE CHOSEN THE LATTER SOLUTION BASED ON THE
THE LOW-LEVEL RIDGE TO NORTH BUILDING SOUTHWARD DUE TO THE COLD AIR
ADVECTION THAT IS EXPECTED BEHIND THE UPPER TROUGH.  THIS IS
CONSISTENT WITH ALL OF THE FORECAST MODELS...EXCEPT THE UKMET WHICH
TAKES JOHN SLOWLY TO THE NORTHEAST.  HOWEVER...ALMOST ALL OF THE
MODELS KEEP JOHN WEST OF 140W LONGITUDE THROUGHOUT THE PERIOD.

JOHN HAS BEEN ABLE TO FIGHT OFF SOME MODERATE TO STRONG SHEAR TODAY
AND NEW DEEP CONVECTION HAS DEVELOPED OVER THE SYSTEM CENTER WHICH
HAD BEEN PARTLY EXPOSED ON THE WEST SIDE. THE SHIPS MODEL BRINGS THE
INTENSITY DOWN QUICKLY AND HAS JOHN A WEAK TROPICAL DEPRESSION IN 72
HOURS.  HOWEVER...WITH DECREASING SHEAR FORECAST IN THE NEXT 36
HOURS...AND JOHN FORECAST TO REMAIN OVER MARGINALLY WARM 26C
SSTS...SOME SLIGHT INTENSIFICATION IS POSSIBLE.  THE OFFICIAL
FORECAST MAINTAINS THE INITIAL INTENSITY THROUGH 24 TO 36
HOURS...WITH ONLY SLIGHT WEAKENING AFTERWARDS DUE TO A GRADUAL
INCREASE IN THE WESTERLY SHEAR.

NOTE...SINCE JOHN IS NOW WEST OF 140W LONGITUDE...THE NEXT AND
FUTURE ADVISORIES WILL BE ISSUED BY THE CENTRAL PACIFIC HURRICANE
CENTER IN HONOLULU HAWAII.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     30/0300Z 17.1N 140.5W    55 KTS
12HR VT     30/1200Z 17.4N 141.1W    55 KTS
24HR VT     31/0000Z 17.5N 141.9W    55 KTS
36HR VT     31/1200Z 17.5N 142.8W    50 KTS
48HR VT     01/0000Z 17.3N 143.5W    50 KTS
72HR VT     02/0000Z 16.5N 143.0W    45 KTS
 
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