MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 01W (VONGFONG) WARNING NR 014// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON 01W (VONGFONG), LOCATED APPROXIMATELY 126 NM SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT 12 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS WELL-ORGANIZED FLARING CENTRAL CONVECTION THAT IS WRAPPING TIGHTLY INTO A CENTER. THE INITIAL INTENSITY IS MAINTAINED AT 65 KNOTS, IN LINE WITH RJTD AND PGTW DVORAK DATA-T ESTIMATES OF T4.0 (65 KTS). THE CONVECTION IMPROVED SLIGHTLY AND FLARED AS TY 01W TRACKED OVER WATER OR SKIRTED THE COAST OF BURIAS ISLAND OVER THE PAST 6 HOURS. THE INITIAL POSITION IS BASED WITH HIGH CONFIDENCE ON RADAR DATA FROM THE PHILIPPINES, WHICH STILL SHOWS A LOW-LEVEL EYE ALTHOUGH IT IS NOT APPARENT IN OVERHEAD SATELLITE IMAGERY. ENVIRONMENTAL PARAMETERS REMAIN FAVORABLE WITH RADIAL OUTFLOW THAT IS PARTICULARLY ENHANCED TO THE NORTH, NEARBY WARM SSTS AND LOW (10-15 KT) VERTICAL WIND SHEAR (VWS). TY 01W HAS TURNED NORTHWESTWARD IN THE PAST 6 HOURS, TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A SUBTROPICAL RIDGE TO THE NORTHEAST. 3. FORECAST REASONING. A. THERE HAS BEEN NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY. HOWEVER, SMALL TRACK CHANGES THAT BRING THE SYSTEM MORE OR LESS OVER WATER OR THE SIGNIFICANT MOUNTAINS OF LUZON MAY HAVE LARGE IMPACTS ON INTENSITY. B. TY 01W IS FORECAST TO TRACK NORTHWESTWARD ALONG THE SOUTHWESTERN PERIPHERY OF THE STEERING STR THROUGH TAU 36. AN UPPER- LEVEL TROUGH TO THE NORTH WILL PASS TO THE NORTH BETWEEN TAU 24-36, ERODING THE STR AND FORCING IT TO RECEDE EASTWARD. THIS WILL CLEAR THE WAY FOR TY 01W TO TURN MORE NORTHWARD AS IT ROUNDS THE STR AXIS BETWEEN TAU 36-48. NUMERICAL MODEL GUIDANCE HAS COME INTO BETTER CROSS TRACK AGREEMENT, WITH THE MAIN GROUPING GOING OVER THE ISLAND OF LUZON. HOWEVER, THERE IS 70 NM OF ALONG-TRACK SPREAD BETWEEN MODELS AT TAU 24, INDICATING SIGNIFICANT PROPAGATION SPEED DIFFERENCES BETWEEN MODEL SOLUTIONS. TY 01W IS EXPECTED TO WEAKEN SIGNIFICANTLY AS IT TRACKS OVER LAND DESPITE ITS FAVORABLE UPPER LEVEL ENVIRONMENT. TY 01W WILL EMERGE OVER 28-30 DEGREE CELSIUS SEA SURFACE TEMPERATURE WATER BY TAU 36. HOWEVER, VWS WILL BEGIN INCREASING AT THAT POINT, AND SYSTEM ORGANIZATION WILL HAVE BEEN DISRUPTED BY THE ROUGH TERRAIN OF LUZON. MODEL INTENSITY GUIDANCE FOR THE PERIOD AFTER TY 01W EMERGES OVER WATER LOWERED ITS EXPECTATIONS THIS RUN, AND THE JTWC FORECAST INTENSITY HAS BEEN LOWERED ACCORDINGLY. AFTER TAU 48, TY 01W WILL BEGIN TO ACCELERATE NORTHEASTWARD. BETWEEN TAU 48-72, TY 01W MAY MAINTAIN INTENSITY AS IT PASSES OVER 27-29 DEGREE CELSIUS WATER AND OUTFLOW IS BRIEFLY ENHANCED AS IT TAPS INTO THE UPPER-LEVEL WESTERLIES TO THE NORTH. C. AFTER TAU 72, HIGH VWS AND CONVERGENCE ALOFT AS TY 01W COMES FULLY UNDER THE UPPER-LEVEL WESTERLIES WILL LEAD TO FURTHER WEAKENING. TY 01W WILL BEGIN TO INTERACT WITH THE BAROCLINIC ZONE AT TAU 72, AND COMPLETE EXTRATROPICAL TRANSITION BY TAU 96. IT IS ALSO POSSIBLE THAT IT DISSIPATES UNDER THE MIDLATITUDE WESTERLIES BEFORE IT CAN COMPLETE EXTRATROPICAL TRANSITION. THERE IS SIGNIFICANT ALONG TRACK SPREAD OF MODEL SOLUTIONS AFTER TAU 72. THE LARGE SPREAD IN MODEL GUIDANCE LENDS LOW CONFIDENCE TO THIS PORTION OF THE JTWC FORECAST TRACK.// NNNN NNNN