WDPN31 PGTW 281500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (HINNAMNOR) WARNING NR 002// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 26.7N 148.3E INITIAL INTENSITY: 45 KTS GEOGRAPHIC REFERENCE: 327 NM EAST OF CHICHI JIMA MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 13 KTS SIGNIFICANT WAVE HEIGHT: 13 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A COMPACT SYSTEM WITH FRAGMENTED SPIRAL BANDING WRAPPING INTO AN 80NM DIAMETER CENTRAL DENSE OVERCAST (CDO) FEATURE, WHICH IS OBSCURING THE LOW-LEVEL CIRCULATION CENTER (LLCC). OTHER THAN A 281137Z AMSU-B 89GHZ MICROWAVE IMAGE, WHICH IS NOT TOO USEFUL, THERE ARE NO OTHER RECENT MICROWAVE IMAGES. HOWEVER, A 281139Z ASCAT-B AMBIGUITY IMAGE SHOWS A WELL-DEFINED CENTER, WHICH SUPPORTS THE INITIAL POSITION WITH HIGH CONFIDENCE. THE INITIAL INTENSITY OF 45 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE HIGH END OF DVORAK ESTIMATES. IN GENERAL, A VARIETY OF ASCAT IMAGES (NOAA, KNMI, NRL) AND A 280802Z SMOS PARTIAL IMAGE SHOW MAXIMUM WINDS RANGING FROM 40-50 KNOTS, THEREFORE, IT IS RECOGNIZED THAT THE INITIAL INTENSITY COULD BE SLIGHTLY HIGHER, ESPECIALLY WITH A DEVELOPING CDO, HOWEVER, THE INITIAL INTENSITY IS REASONABLE BASED ON THE CONVECTIVE STRUCTURE IN THE AMSU-B MICROWAVE IMAGE AND SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES. UPPER-LEVEL CONDITIONS REMAIN FAVORABLE WITH FAIR POLEWARD OUTFLOW, ROBUST EQUATORWARD OUTFLOW AND LOW VERTICAL WIND SHEAR (VWS). SST VALUES (30-31C) REMAIN CONDUCIVE. INITIAL WIND RADII BASIS: SCATTEROMETER DATA CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTH (EXTENSION OF THE STR) AND NORTHEAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS RJTD: T2.0 - 30 KTS KNES: T3.0 - 45 KTS CIMSS ADT: 39 KTS AT 281340Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 30-31 CELSIUS OUTFLOW: STRONG EQUATORWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: SHIFTED THE 4-DAY TO 5-DAY FORECAST TRACK FURTHER SOUTH AND SLOWED TRACK SPEEDS NEAR OKINAWA. INCREASED THE PEAK INTENSITY BASED ON HWRF AND COAMPS-TC DATA. FORECAST DISCUSSION: TS 12W IS FORECAST TO TURN GRADUALLY WEST-NORTHWESTWARD TO WESTWARD OVER THE NEXT 12 TO 24 HOURS AS THE STR BUILDS TO THE NORTH. A DEEP MIDLATITUDE SHORTWAVE TROUGH CURRENTLY POSITIONED OVER NORTHEASTERN JAPAN IS KICKING NORTHEASTWARD WITH A MIDLATITUDE RIDGE BUILDING OVER KOREA AND WESTERN JAPAN, WHICH WILL REINFORCE THE BUILDING STR. AFTER TAU 48, THE SYSTEM IS NOW EXPECTED TO TURN WEST-SOUTHWESTWARD TOWARD THE RYUKYU ISLANDS WITH A SIGNIFICANT DECREASE IN TRACK SPEEDS AFTER TAU 72 AS AN APPROACHING MIDLATITUDE TROUGH WEAKENS THE STEERING RIDGE. THERE IS ALSO SOME POTENTIAL FOR COMPETING STEERING INFLUENCES, WHICH MAY LEAD TO A QUASI-STATIONARY OR ERRATIC TRACK MOTION AFTER TAU 72. ENVIRONMENTAL CONDITIONS ARE EXPECTED TO REMAIN FAVORABLE THUS STEADY INTENSIFICATION IS ANTICIPATED WITH A PEAK OF 100 KNOTS BY TAU 96. MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE REMAINS IN POOR AGREEMENT WITH A BIFURCATION IN THE MODEL TRACKERS. NAVGEM AND AFUM RECURVE THE SYSTEM OVER WESTERN JAPAN WHILE THE BULK OF THE REMAINING GUIDANCE INDICATES A SOUTHWESTWARD TRACK TOWARD THE RYUKYU ISLANDS. THE 280600Z ECMWF ENSEMBLE (EPS) AND GFS ENSEMBLE (GEFS) ALSO INDICATE HIGH UNCERTAINTY IN THE TRACK AFTER TAU 72. EPS SHOWS A WIDE SPREAD OF SOLUTIONS THAT RECURVE THE SYSTEM NORTH OF OKINAWA OR STALL THE SYSTEM SOUTH OF OKINAWA. GEFS IS BIFURCATED WITH HALF THE SOLUTIONS RECURVING THE SYSTEM OVER WESTERN JAPAN AND THE OTHER HALF STALLING THE SYSTEM SOUTH OF OKINAWA. THIS HIGH DEGREE OF UNCERTAINTY IS RELATED TO THE TIMING AND IMPACT OF THE MIDLATITUDE SHORTWAVE TROUGH WITH SIGNIFICANT DIFFERENCES IN THE ORIENTATION AND STRENGTH OF THE STR AS WELL AS POTENTIAL BINARY INTERACTION WITH A WEAK SYSTEM TO THE SOUTH OF TS 12W, WHICH PULLS MANY TRACKERS SHARPLY SOUTHWESTWARD. CONSEQUENTLY, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST TRACK AND LOW CONFIDENCE IN THE JTWC INTENSITY FORECAST, WHICH COULD BE HIGHER IF THE SYSTEM STALLS OVER WARM WATER SOUTH OF OKINAWA. FORECAST CONFIDENCE: TRACK 0 - 72 HR: LOW TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: LOW INTENSITY 72-120 HR: LOW// NNNN