WDPN31 PGTW 212100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (SANVU) WARNING NR 010// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 10.3N 155.3E INITIAL INTENSITY: 40 KTS GEOGRAPHIC REFERENCE: 643 NM EAST-SOUTHEAST OF ANDERSEN AFB MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 04 KTS SIGNIFICANT WAVE HEIGHT: 16 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED PROXYVIS SATELLITE IMAGERY DEPICTS A SMALL, EXPOSED MESOVORTEX NEAR 10.37N 154.34E LOCATED ON THE WESTERN PERIPHERY OF AN ELONGATED LOW-LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS HEDGED EAST OF THE MESOVORTEX WITHIN THE BROAD, EXPOSED LLCC, WHICH IS DE-COUPLED WEST OF A LARGE CLUSTER OF FAIRLY DISORGANIZED DEEP CONVECTION DUE TO MODERATE TO HIGH (20-25 KNOTS) MID-LEVEL VERTICAL WIND SHEAR. A 211522Z AMSR2 89GHZ MICROWAVE IMAGE REVEALS A CURVED BAND OF DEEP CONVECTION (ASSOCIATED WITH STRONG LOW-LEVEL CONVERGENT FLOW) OVER THE EASTERN PERIPHERY WITH A WEAKLY DEFINED LLCC JUST WEST OF THE NORTHERN PORTION OF THE BAND. DUE TO THE LACK OF RECENT ASCAT IMAGERY AND HIGH-RESOLUTION MICROWAVE IMAGERY, THERE IS MEDIUM CONFIDENCE IN THE INITIAL POSITION. THE INITIAL INTENSITY OF 40 KNOTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE RANGE OF DATA-T ESTIMATES AND CURRENT INTENSITY ESTIMATES (35-45 KNOTS) AS WELL AS ADT AND AIDT ESTIMATES (43 KNOTS, 38 KNOTS). OPEN-AIIR AND DMN ESTIMATES REMAIN VERY LOW AT 30 KNOTS. INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK CURRENT STEERING MECHANISM: WEAK LOW- TO MID-LEVEL SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTH AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS RJTD: T3.0 - 45 KTS KNES: T3.0 - 45 KTS CIMSS ADT: 43 KTS AT 211900Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL VWS: 15-20 KTS SST: 28-29 CELSIUS OUTFLOW: MODERATE POLEWARD AND EQUATORWARD OTHER FACTORS: DRY AIR ENTRAINMENT ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM 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: TS 01W WILL TRACK SLOWLY WESTWARD THROUGH TAU 24 UNDER A WEAK STEERING RIDGE, HOWEVER, THE STR IS EXPECTED TO BUILD TO THE NORTH WHICH WILL ACCELERATE THE SHALLOW SYSTEM WESTWARD AFTER TAU 24. TS 01W IS FORECAST TO WEAKEN STEADILY THROUGH THE FORECAST PERIOD DUE TO PERSISTENT MID-LEVEL VERTICAL WIND SHEAR AND DRY AIR ENTRAINMENT. THE SYSTEM IS EXPECTED TO DISSIPATE WITHIN THE NEXT 72 TO 96 HOURS WITH THE REMANANTS TRACKING JUST SOUTH OF GUAM. ALTHOUGH THE SYSTEM IS EXPECTED TO DISSIPATE BELOW TROPICAL DEPRESSION STRENGTH, GRADIENT WINDS ALONG THE NORTHERN PERIPHERY OF THE SYSTEM AND ENHANCED, DISORGANIZED DEEP CONVECTION WILL LIKELY CONTINUE AS THE SYSTEM APPROACHES AND PASSES NEAR GUAM. MODEL DISCUSSION: WITH THE EXCEPTION OF NAVGEM, WHICH INDICATES A WEST-NORTHWESTWARD TRACK OVER THE NORTHERN MARIANAS, NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT INDICATING A GENERALLY WESTWARD TRACK. THE BULK OF THE RELIABLE INTENSITY GUIDANCE INDICATES STEADY WEAKENING THROUGH THE FORECAST PERIOD AND SUPPORTS THE JTWC INTENSITY FORECAST WITH HIGH CONFIDENCE. BOTH THE EPS (ECMWF ENSEMBLE) AND GEFS (GFS ENSEMBLE) INDICATE A VERY LOW (LESS THAN 10 PERCENT) PROBABILITY OF A TROPICAL DEPRESSION NEAR GUAM, WHICH IS IN LINE WITH THE JTWC FORECAST PHILOSOPHY. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: HIGH INTENSITY 72-120 HR: HIGH// NNNN