WDPN31 PGTW 062100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 24W (YINXING) WARNING NR 015// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 18.3N 123.6E INITIAL INTENSITY: 115 KTS GEOGRAPHIC REFERENCE: 268 NM NORTHEAST OF MANILA, PHILIPPINES MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 04 KTS SIGNIFICANT WAVE HEIGHT: 36 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON 24W (YINXING) TRACKING SLOWLY WEST-NORTHWESTWARD OVER THE PAST 6 HOURS, TOWARD THE NORTHERN COAST OF LUZON, WITH AN INCREASINGLY SYMMETRIC CENTRAL DENSE OVERCAST (CDO) COVERING THE EYEWALL. THE 20 NM EYE HAS ALSO BECOME MORE CIRCULAR IN SHAPE AND THE EDGES ARE CLEANER, SUGGESTING INTENSIFICATION. ROBUST POLEWARD OUTFLOW, ENHANCED BY THE JET TO THE NORTH, IS APPARENT IN THE ANIMATED IMAGERY AS WELL. ENVIRONMENTAL ANALYSIS INDICATES THAT 24W IS IN A FAVORABLE ENVIRONMENT CHARACTERIZED BY THE STRONG POLEWARD OUTFLOW ALOFT, LOW (10-15 KTS) VERTICAL WIND SHEAR, AND WARM (27-28 C) SEA SURFACE TEMPERATURES. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE DEFINED EYE IN THE ANIMATED EIR SATELLITE IMAGERY. THE INITIAL INTENSITY OF 115 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW. INITIAL WIND RADII BASIS: SAR DATA CURRENT STEERING MECHANISM: PLACED WITHIN A WEAK STEERING ENVIRONMENT BETWEEN AN EXTENSION OF THE SUBTROPICAL RIDGE TO THE EAST-NORTHEAST AND A RIDGE CENTERED NEAR HONG KONG. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T6.0 - 115 KTS RJTD: T6.0 - 115 KTS RCTP: T6.0 - 115 KTS KNES: T6.0 - 115 KTS DEMS: T6.0 - 115 KTS CIMSS ADT: 122 KTS AT 061800Z CIMSS AIDT: 114 KTS AT 061800Z CIMSS DPRINT: 108 KTS AT 061800Z CIMSS DMINT: 114 KTS AT 061716Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 10-15 KTS SST: 27-28 CELSIUS OUTFLOW: STRONG POLEWARD OTHER FACTORS: NEARING THE NORTHERN COAST OF LUZON, SO TERRAIN INTERACTION WILL SOON BECOME A FACTOR. ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: 24W IS FORECAST TO BEGIN TRACKING MORE QUICKLY WESTWARD, SKIRTING THE NORTHERN COAST OF LUZON, AS THE RIDGE CENTERED OVER HONG KONG EXTENDS EASTWARD AND BECOMES THE PRIMARY STEERING MECHANISM. LANDFALL ALONG THE NORTHEASTERN COAST OF LUZON IS EXPECTED NEAR TAU 12. A WESTWARD TRACK IS THEN FORECAST THROUGH TAU 72. NEAR TAU 72, ANOTHER RIDGE CENTERED OVER THAILAND AND LAOS WILL EXTEND OVER TO THE SOUTH CHINA SEA, CAUSING 24W TO TURN SOUTHWESTWARD. REGARDING INTENSITY, 24W IS FORECAST TO BEGIN A WEAKENING TREND THROUGH THE FORECAST PERIOD. AS THE SYSTEM APPROACHES THE COAST OF LUZON, TERRAIN INTERACTION WILL BEGIN TO WEAKEN IT. ADDITIONALLY, A COLD SURGE FLOWING SOUTHWESTWARD NEAR TAIWAN WILL BRING IN COLD AND DRY AIR WHICH WILL FURTHER AID IN WEAKENING THE SYSTEM. HOWEVER, AFTER TAU 24, 24W WILL ENTER THE SOUTH CHINA SEA AND THE COLD SURGE IS EXPECTED TO WEAKEN, ALLOWING THE VORTEX TO REMAIN STRONG. AS THE SYSTEM TRACKS WESTWARD BETWEEN TAU 36-72 THE ENVIRONMENT IS FORECAST TO REMAIN OVERALL FAVORABLE. AFTER TAU 72, THE ENVIRONMENT IS EXPECTED TO QUICKLY WORSEN DUE TO INCREASING SOUTHWESTERLY VERTICAL WIND SHEAR AND SIGNIFICANT DRY AIR ENTRAINMENT. AS A RESULT, THE VORTEX WILL RAPIDLY DEGRADE AS IT BECOMES DECOUPLED NEAR THE END OF THE FORECAST PERIOD. MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN TIGHT AGREEMENT REGARDING THE TRACK OF 24W THROUGH TAU 72, WITH A MERE 50 NM CROSS-TRACK SPREAD AT THAT TIME. AFTER TAU 72, MODELS BEGIN TO DIVERGE AS THE VORTEX RAPIDLY WEAKENS. AT TAU 120 CROSS-TRACK SPREAD INCREASES TO 240 NM. OVERALL, THERE ARE NO SIGNIFICANT OUTLIERS REGARDING THE TRACK OF 24W THROUGH TAU 120. INTENSITY GUIDANCE, ON THE OTHER HAND, IS IN POOR AGREEMENT. HAFS-A SUGGESTS FURTHER INTENSIFICATION THROUGH TAU 36 TO A PEAK OF 125 KTS AT TAU 36 DUE TO A SLIGHTLY MORE NORTHERN TRACK THROUGH THE LUZON STRAIT AND THEREFORE LESS LAND INTERACTION. GFS HAS A MUCH MORE RAPID WEAKENING TREND THROUGH TAU 72 AND ECMWF HAS A MORE GRADUAL WEAKENING TREND. THE JTWC INTENSITY FORECAST IS PLACED CLOSE TO THE HWRF, WHICH DEPICTS A GRADUAL WEAKENING THROUGH TAU 72 AND RAPID WEAKENING THEREAFTER. THE JTWC INTENSITY FORECAST IS PLACED WITH OVERALL LOW CONFIDENCE DUE TO THE LARGE SPREAD IN GUIDANCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: LOW INTENSITY 72-120 HR: LOW// NNNN