WDPN31 PGTW 301500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (NYATOH) WARNING NR 005// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 12.9N 137.5E INITIAL INTENSITY: 40 KTS GEOGRAPHIC REFERENCE: 207 NM NORTH OF YAP MOVEMENT PAST 6 HOURS: WESTWARD AT 06 KTS SIGNIFICANT WAVE HEIGHT: 19 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A CONSOLIDATING SYSTEM WITH STRONG RADIAL OUTFLOW AS WELL AS A ROBUST POLEWARD OUTFLOW CHANNEL AND SUSTAINED CONVECTION WHICH HAS FURTHER DEEPENED OVER THE PAST SIX HOURS. THE INITIAL POSITION IS BASED ON THE PGTW POSITION FIX AND THE INITIAL INTENSITY OF 40 KTS IS HEDGED SLIGHTLY LOWER THAN THE PGTW DVORAK CURRENT INTENSITY ESITMATE OF T3.0 (45 KTS) BASED ON A 300854Z SMOS IMAGE SHOWING 34-37 KT WINDS IN THE NORTHEASTERN QUADRANT. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: THE DEEP LAYERED SUBTROPICAL RIDGE TO THE NORTHWEST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS RJTD: T2.0 - 30 KTS RCTP: T3.0 - 45 KTS KNES: T3.0 - 45 KTS CIMSS SATCON: 53 KTS AT 300926Z CIMSS ADT: 53 KTS AT 301140Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE VWS: 5-10 KTS SST: 29-30 CELSIUS OUTFLOW: STRONG RADIAL 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: TROPICAL STORM 27W WILL BEGIN TO TRACK NORTHWESTWARD WITHIN THE NEXT 24 HOURS BEFORE BEGINNING A MORE NORTHWARD TRACK AS IT ROUNDS THE SUBTROPICAL RIDGE AXIS AROUND TAU 36 TO TAU 48. AFTER TAU 48, THE SYSTEM WILL BEGIN TO ACCELERATE NORTHEASTWARD UNDER THE INFLUENCE OF A DEEP MID-LATITUDE TROUGH PASSING TO THE NORTH. DUE TO INCREASINGLY ROBUST OUTFLOW PAIRED WITH HIGHLY FAVORABLE OCEAN HEAT CONTENT AND LOW VERTICAL WIND SHEAR, TS 27W WILL UNDERGO A PERIOD OF RAPID INTENSIFICATION FROM TAU 12 TO TAU 36. THE CURRENT FORECAST PEAKS THE INTENSITY AT 95 KTS AT TAU 48, HOWEVER, IT IS LIKELY THAT THE SYSTEM WILL REACH 105 KTS SOMETIME BETWEEN FORECAST TAUS 48 AND 72. AFTERWARDS, INCREASING VERTICAL WIND SHEAR FROM THE MID-LATITUDE TROUGH TO THE NORTH WILL BEGIN TO WEAKEN THE SYSTEM TO 85 KTS BY TAU 72. IN ADDITION TO WEAKENING THE SYSTEM, THE VERTICAL WIND SHEAR FROM THE MID-LATITUDE TROUGH IS EXPECTED INITIATE A DECOUPLING PROCESS FOR THE CIRCULATION. THIS IS EXPECTED TO OCCUR AFTER TAU 96 WITH THE REMAINING LOW LEVEL CIRCULATION, NOW UNDER THE INFLUENCE OF LOW LEVEL STEERING FEATURES, BEING DRIVEN SOUTHWESTWARD. MODEL DISCUSSION: IN REGARDS TO FORECAST INTENSITY, BOTH DETERMINISTIC AND ENSEMBLE MODELS ARE GENERALLY IN GOOD AGREEMENT AS FAR AS THE TREND OF INTENSIFICATION. THE PAST COUPLE RUNS HAVE DEPICTED A PERIOD OF MODERATE TO RAPID INTENSIFICATION UP TO TAU 48 WITH PEAK INTENSITY BETWEEN TAUS 48 AND 60 AND A MODERATE TO RAPID WEAKENING FOR THE REMAINDER OF THE FORECAST. THE RANGE OF PEAK INTENSITY VARIES WITH GFS PEAKING AT ABOUT 75 KTS AND CTCI AND HWRF PEAKING AT 120 KTS. THE FORECAST INTENSITY IS THEREFORE BASED OFF OF THE CONSENSUS. IN REGARDS TO FORECAST TRACK, THE MODELS ARE SPLIT BETWEEN TWO POSSIBLE SCENARIOS. THE GFS DETERMINISTIC, GFS ENSEMBLE, EGRR, AND AFUM DEPICT A DECOUPLING SCENARIO AROUND TAU 96, WHICH THE FORECAST TRACK CURRENTLY REFLECTS. ALTERNATIVELY, THE ECMWF DETERMINISTIC, ECMWF ENSEMBLE, AND NVGM DEPICT A SCENARIO WHERE THE SYSTEM IS PULLED NORTHEASTWARD AFTER TAU 96 IN THE WAKE OF THE MID-LATITUDE TROUGH AND DISSIPATES OR UNDERGOES EXTRATROPICAL TRANSITION. OF NOTE, WHILE THERE IS NOT GOOD AGREEMENT OVER THE FORECAST TRACK, THE LAST COUPLE MODEL RUNS HAVE REMAINED FAIRLY CONSISTENT. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN