WDPN32 PGTW 212100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 11W (SHANSHAN) WARNING NR 002// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 17.4N 142.3E INITIAL INTENSITY: 30 KTS GEOGRAPHIC REFERENCE: 201 NM WEST OF ALAMAGAN MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 06 KTS SIGNIFICANT WAVE HEIGHT: 12 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A GROWING CENTRAL DENSE OVERCAST OBSCURING A DEVELOPING LOW LEVEL CIRCULATION CENTER (LLCC), WITH FRAGMENTED, FORMATIVE BANDS WRAPPING FROM THE SOUTHERN PERIPHERY. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON FIXES FROM PGTW AND KNES, AND SUPPORTED BY THE CENTRAL CONVECTIVE BANDING STRUCTURES SEEN IN 211606Z AMSR-2 DATA, HOWEVER, THE GFS MODEL INDICATES THE MID-LEVEL VORTEX IS NOT ALIGNED WITH THE LLCC, INDUCING SOME UNCERTAINTY. THE INITIAL INTENSITY WAS ASSESSED AT 30 KNOTS WITH MEDIUM CONFIDENCE, BASED ON ALL AGENCY DVORAK ESTIMATES OF T2.0 (30 KNOTS), AND SUPPORTED BY THE 30-33 KNOT ESTIMATES FROM OBJECTIVE GUIDANCE AIDS. ANALYSIS INDICATES A GENERALLY FAVORABLE ENVIRONMENT WITH WARM (30 DEGREE C) SST AND MODERATE EQUATORWARD OUTFLOW AND LIGHT (10-15 KNOT) VERTICAL WIND SHEAR CONDITIONS. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: LOW TO MID-LEVEL REFLECTION OF A WEAK SUBTROPICAL RIDGE TO THE EAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.0 - 30 KTS RJTD: T2.0 - 30 KTS RCTP: T2.0 - 30 KTS KNES: T2.0 - 30 KTS CIMSS SATCON: 32 KTS AT 211615Z CIMSS ADT: 30 KTS AT 211730Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 10-15 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE EQUATORWARD ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: NOT APPLICABLE 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: INITIALLY TD 11W (SHANSHAN) WILL TRACK GENERALLY NORTH-NORTHWESTWARD UNDER THE INFLUENCE OF THE WEAK STR. SLOW INTENSIFICATION IS EXPECTED WHILE THE SYSTEM BECOMES MORE ORGANIZED AND ALIGNED VERTICALLY. BY TAU 48, OUTFLOW WILL IMPROVE THANKS TO A TUTT CELL TO THE NORTHEAST, LEADING TO AN INCREASED RATE OF INTENSIFICATION. BY TAU 72, THE STR SHOULD STRENGTHEN RESULTING IN A SLIGHT NORTHWESTWARD DEFLECTION, PUTTING THE SYSTEM ON A TRACK TOWARDS JAPAN (BEYOND THE EXTENT OF THIS FORECAST). THE INTENSITY SITUATION WILL BECOME MORE COMPLEX AS THE TUTT CELL MOVES OFF AND A NEW UPPER LOW DEEPENS TO THE WEST. GFS MAINTAINS ENOUGH SEPARATION DISTANCE THAT THE UPPER LOW WILL ENHANCE OUTFLOW AND ALLOW FOR RAPID INTENSIFICATION, WHILE ECMWF DEPICTS THE LOW HAMPERING OUTFLOW, CAPPING SHANSHANS DEVELOPMENT. GIVEN OVERALL FAVORABLE CONDITIONS, THE OFFICIAL FORECAST FAVORS THE GFS SOLUTION AND INTENSIFIES THE SYSTEM THROUGHOUT THE FORECAST DURATION. MODEL DISCUSSION: THE INITIAL MODEL SPREAD IS FAIRLY HIGH DUE TO THE WEAK STEERING INFLUENCE, WITH GFS BEING AN OUTLIER TO THE EAST, TRACKING INTO THE STR. THE FORECAST TRACK WAS PLACED CLOSE TO THE MULTI-MODEL MEAN AND NEAR THE PREVIOUS FORECAST. EVENTUALLY THE GFS SOLUTION CONVERGES BACK TO THE REST OF THE CONSENSUS MEMBER GROUPING. ENSEMBLE MODEL SPREAD ALSO DEVIATES SIGNIFICANTLY, BUT OVERWHELMING FAVORS A STRAIGHT RUNNING TRACK SOLUTION TOWARDS JAPAN, VICE ROUNDING THE STR DURING THE 120 HOUR FORECAST PERIOD. DUE TO INITIAL UNCERTAINTY WITH LARGE MODEL SPREAD AND THE SLOW LOW LEVEL VORTEX DEVELOPMENT, THERE IS MEDIUM CONFIDENCE IN THE JTWC TRACK FORECAST. THERE IS MEDIUM CONFIDENCE IN THE INTENSITY FORECAST TO TAU 72, THEN LOW CONFIDENCE AFTERWARD GIVEN THE COMPETING MODEL SOLUTION PLACEMENT OF AN UPPER LOW, IMPACTING THE FUTURE INTENSIFICATION RATE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN