WDPN31 PGTW 020300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (JEBI) WARNING NR 
09//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 09W (JEBI), LOCATED APPROXIMATELY 435 NM EAST-
SOUTHEASTWARD OF HANOI, VIETNAM, HAS TRACKED NORTH-NORTHWESTWARD AT 
09 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE 
IMAGERY (MSI) SHOWS MARGINAL IMPROVEMENTS IN THE OVERALL STRUCTURE 
OF THE MONSOON DEPRESSION AS THE CONSOLIDATING LOW-LEVEL CIRCULATION 
CENTER (LLCC) TRACKS TOWARDS HAINAN ISLAND. MSI SHOWS A PARTIALLY 
EXPOSED LLCC WITHIN THE NORTHWEST QUADRANT OF THE SYSTEM. DUE TO 
MODERATE LEVELS OF VERTICAL WIND SHEAR (VWS) (15 TO 20 KNOTS) 
ASSOCIATED WITH THE DEEP LAYERED UPPER LEVEL SUBTROPICAL RIDGE (STR) 
TO THE NORTH, THE MAJORITY OF DEEP CONVECTION REMAINS LOCATED WITHIN 
THE SOUTHERN HALF OF THE SYSTEM. UPPER AIR SOUNDINGS FROM HAIKOU, 
HAINAN INDICATE STRONG EASTERLY FLOW DOMINATES THE STEERING 
ENVIRONMENT AS TS 09W MOVES CLOSER TO THE ISLAND. THE TRACK SPEED 
FOR TS 09W HAS INCREASED OVER THE PAST SIX HOURS AS THE STR 
INTERACTS MORE WITH THE SYSTEM.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE 
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. OVER THE NEXT 12 HOURS, THE TRACK FOR TS 09W IS EXPECTED TO 
FLATTEN TOWARDS THE WEST-NORTHWEST UNDER THE INFLUENCE OF THE DEEP 
LAYERED STR, WITH A SLIGHT INCREASE IN THE OVERALL TRACK SPEED. 
CURRENT FORECAST GUIDANCE INDICATES TS 09W WILL MAKE LANDFALL OVER 
HAINAN WITHIN THE NEXT 12 TO 18 HOURS. INTENSITY GUIDANCE SUPPORTS 
THE RECENT IMPROVING ORGANIZATIONAL TRENDS OBSERVED IN MSI, AND 
INDICATES INTENSIFICATION OVER THE NEXT 12 HOURS AS VWS REMAINS AT 
MODERATE LEVELS WITH GOOD EQUATORWARD UPPER LEVEL OUTFLOW. AS THE 
SYSTEM PASSES OVER HAINAN, A SLIGHT WEAKENING TREND IS EXPECTED DUE 
TO THE FRICTIONAL LAND EFFECTS DE-STABILIZING THE LOW LEVEL INFLOW. 
GREATER INTERACTION WITH THE STR WILL LEAD TO INCREASING TRACK 
SPEEDS AND THE COMBINATION WITH STEADY VWS WILL MITIGATE THE 
POSSIBILITY OF STRONGER INTENSIFICATION OF THE SYSTEM AFTER MOVING 
BACK INTO THE GULF OF TONKIN. LANDFALL INTO NORTHERN VIETNAM IS 
EXPECTED SLIGHTLY BEFORE TAU 36, WITH THE COMPLETE DISSIPATION OF 
THE SYSTEM BY TAU 48 DUE TO FRICTIONAL LAND EFFECTS. MODEL GUIDANCE 
REMAINS IN GOOD AGREEMENT WITH THIS SCENARIO, LEADING TO HIGH 
CONFIDENCE IN THE FORECAST TRACK.//
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