WDPN31 PGTW 202100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 25W (TWENTYFIVE) WARNING NR 005// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 20.5N 126.1E INITIAL INTENSITY: 30 KTS GEOGRAPHIC REFERENCE: 372 NM SOUTH-SOUTHWEST OF KADENA AB MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS SIGNIFICANT WAVE HEIGHT: 14 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY INDICATES THE SYSTEM IS DISORGANIZED WITH A LARGE CLUSTER OF PERSISTENT DEEP CONVECTION EXTENDING OVER THE SOUTHWESTERN SEMICIRCLE OF A BROAD LOW-LEVEL CIRCULATION. ADDITIONALLY, WATER VAPOR IMAGERY INDICATES A RELATIVELY DRY STABLE AIR MASS TO THE NORTH, WITH MODERATE EQUATORWARD OUTFLOW TO THE SOUTH OF THE SYSTEM. THESE ENVIRONMENTAL FACTORS CONTINUE TO PREVENT RAPID CONSOLIDATION AND STRENGTHENING. THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON ANIMATED EIR, ALONG WITH AN EARLIER 201324Z PARTIAL ASCAT-B, WHICH SHOWS AN ELONGATED HIGHLY ASYMMETRICAL CIRCULATION, WITH 25-30 KNOTS ON THE NORTHEASTERN PERIPHERY, WITH LIGHTER WINDS ON THE SOUTHERN PERIPHERY. THE INITIAL INTENSITY OF 30 KNOTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE EARLIER ASCAT-B ALONG WITH A COMBINATION OF OBJECTIVE AND SUBJECTIVE DVORAK INTENSITY ESTIMATES WHICH ARE ON THE HIGH END OF INTENSITY ESTIMATES. ENVIRONMENTAL CONDITIONS ARE MARGINALLY FAVORABLE WITH DRY STABLE AIR TO THE NORTH, MODERATE EQUATORWARD OUTFLOW, WARM (29-30C) SEA SURFACE TEMPERATURES (SSTS), AND LOW (0-5KTS) VERTICAL WIND SHEAR (VWS). INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR) CENTERED OVER TAIWAN. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T1.5 - 25 KTS RJTD: T1.0 - 25 KTS CIMSS SATCON: 38 KTS AT 201333Z CIMSS ADT: 39 KTS AT 201740Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 0-5 KTS SST: 28-29 CELSIUS OUTFLOW: MODERATE EQUATORWARD OTHER FACTORS: DRY STABLE AIR ON THE NORTHWESTERN PERIPHERY OF CIRCULATION 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: OVER THE PAST SIX HOURS TD 25W CONTINUES TO TRACK GENERALLY WESTWARD ALONG THE SOUTHEASTERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) POSITIONED OVER TAIWAN. THIS GENERAL WESTWARD TRACK WILL CONTINUE THROUGH TAU 24. THEN BY TAU 36, THE SYSTEM WILL PASS THROUGH THE LUZON STRAIGHT WITH A SLIGHT TRACK POLEWARD AS A WEAK TROUGH PASSES TO THE NORTH THAT WILL INDUCE A WEAKNESS WITHIN THE STEERING RIDGE. BY TAU 48, 25W WILL TRANSIT INTO THE SOUTH CHINA SEA AND REACH AN INFLECTION POINT WHEREBY THE PRIMARY STEERING MECHANISM BECOMES A DEEP LAYER RIDGE OVER EAST CHINA. THIS STEERING MECHANISM WILL THEN STEER THE SYSTEM GENERALLY SOUTHWESTWARD THROUGH THE REMAINED OF THE FORECAST PERIOD. TD 25W WILL SLOWLY INTENSIFY THROUGH THE NEXT 24 HOURS DUE TO THE INITIAL HIGHLY ASYMMETRICAL LLCC ALONG WITH THE DRY STABLE AIR OVER THE NORTHERN PERIPHERY. HOWEVER, ENVIRONMENTAL CONDITIONS ARE FORECAST TO IMPROVE BETWEEN TAU 36 AND TAU 72, AS THE SYSTEM WILL MOVE INTO A MORE CONDUCIVE ENVIRONMENTAL WITH IMPROVED UPPER-LEVEL OUTFLOW WHICH WILL ALLOW FOR A FAST INTENSIFICATION PERIOD. AFTER TAU 72, DECREASING SEA SURFACE TEMPERATURES (SSTS) LEFT IN THE WAKE OF TY 23W ALONG WITH UPPER-LEVEL CONVERGENT EASTERLY FLOW WILL RESULT IN STEADY WEAKENING THROUGH TAU 120. MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE REMAINS IS IN GOOD AGREEMENT WITH THE EXCEPTION OF COTI AND NAVGEM WHICH REMAIN THE NORTHERN OUTLIERS THROUGH TAU 72. BETWEEN TAU 96 AND TAU 120 UNCERTAINLY IN TRACK GUIDANCE INCREASE TO A 370NM CROSS-TRACK SPREAD. ADDITIONALLY, THE GFS ENSEMBLE (GEFS) SOLUTIONS SUPPORT THE JTWC FORECAST TRACK THROUGH TAU 72, WITH INCREASING CROSS-TRACK SPREAD BY TAU 120. THEREFORE, THE JTWC FORECAST TRACK IS POSITIONED CLOSE TO THE MULTI-MODEL CONSENSUS WITH MEDIUM CONFIDENCE. THE INTENSITY GUIDANCE IS IN FAIR AGREEMENT AND SUPPORTS AN INTENSIFICATION PHASE THROUGH TAU 72 WITH HWRF INDICATING A PEAK INTENSITY NEAR 80 KNOTS AND COAMPS-TC (GFS VERSION) INDICTING A PEAK INTENSITY OF 60 KNOTS, WHICH IS MORE INLINE WITH THE INTENSITY CONSENSUS PEAK OF 60 KNOTS. COMAMPS-TC EPS INDICATES HIGH PROBABILITY OF MODERATE INTENSIFICATION AND A 70 PERCENT CHANCE OF RAPID INTENSIFICATION (RI) BETWEEN TAU 48 AND TAU 72. WHEREAS THE GEFS SHOWS A MORE MODERATE INTENSIFICATION FROM TAU 48 THROUGH TAU 72 GIVEN THE UNCERTAINLY IN THE INTENSITY DURING THIS TIME-FRAME, THE JTWC FORECAST INTENSITY IS PLACED WITH LOW CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN