WDPN32 PGTW 271500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (JEBI) WARNING NR 005// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 18.4N 144.9E INITIAL INTENSITY: 40 KTS GEOGRAPHIC REFERENCE: 433 NM SOUTH-SOUTHEAST OF IWO TO MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 03 KTS SIGNIFICANT WAVE HEIGHT: 16 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS THAT THE LOW LEVEL CIRCULATION CENTER (LLCC) ASSOCIATED WITH TROPICAL STORM (TS) JEBI IS NOW OBSCURED, HAVING TUCKED UNDER A CENTRAL DENSE OVERCAST FEATURE WHICH HAS PERSISTED FOR THE LAST SIX HOURS OR SO. THE EXTREME OUTER BANDS OF THE LLCC ARE JUST VISIBLE TO THE NORTHWEST OF THE CDO FEATURE BUT DO NOT PROVIDE ENOUGH EVIDENCE TO DEFINE THE LLCC WITH CONFIDENCE. EIR CLOUD TOP TEMPERATURES IN THE CDO ARE EXCEEDING -80C IN SEVERAL OF THE STRONGEST HOT TOWERS. A PARTIAL 271052Z ASCAT PASS CAUGHT THE EASTERN PORTION OF THE CENTER AND SHOWED A LARGE AREA OF 35-45 KNOT WINDS ALONG THE EASTERN SEMICIRCLE OF THE CIRCULATION. THE PARTIAL PASS SAW JUST ENOUGH OF THE CENTER TO INCREASE CONFIDENCE IN THE INITIAL POSITION TO MEDIUM. THE INITIAL INTENSITY WAS ASSESSED WITH MEDIUM CONFIDENCE, HEDGED SLIGHTLY HIGHER THAN THE BULK OF AGENCY INTENSITY ESTIMATES AND THE CIMSS OBJECTIVE ESTIMATES IN LIGHT OF THE ASCAT PASS MENTIONED ABOVE. ANIMATED WATER VAPOR IMAGERY SHOWS A TUTT-CELL SITUATED ABOUT 350NM NORTHEAST OF THE SYSTEM, BUT CIMSS AMV DATA SHOWS THE TUTT IS STRETCHING OUT AND WEAKENING MORE THAN ANTICIPATED. THE ASSUMED REDUCTION IN DEEP-LAYER SHEAR IS ONE REASON WHY THE CDO HAS BEEN ABLE TO PERSIST AND EXPAND UPSHEAR OVER THE PAST SIX HOURS. THE WATER VAPOR IMAGERY ALSO SHOWS THE BEGINNINGS OF A POLEWARD OUTFLOW CHANNEL INTO THE EASTERN PORTION OF THE TUTT-CELL, PROVIDING AN ADDITIONAL BOOST TO TS 19W. THE ENVIRONMENT REMAINS MARGINAL, DUE TO THE LIKELY PRESENCE OF SIGNIFICANT MID-LEVEL NORTHWESTERLY SHEAR, DRY MID-LEVEL AIR OVER THE NORTHWESTERN PORTION OF THE SYSTEM AND CONVERGENT FLOW ALOFT EMANATING FROM THE TUTT-CELL. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS RJTD: T2.0 - 30 KTS CIMSS ADT: 34 KTS AT 271140Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL VWS: 10-15 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE POLEWARD AND EQUATORWARD OTHER FACTORS: DRY MID-LEVEL AIR AND CONVERGENT FLOW TO THE NORTH. ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TRACK MOTION HAS SLOWED CONSIDERABLY OVER THE LAST SIX HOURS AS THE LLCC HAS SHIFTED POSITION TO TUCKED BACK UNDER THE CONVECTION. HOWEVER, THE OVERALL STEERING INFLUENCE REMAINS THE STR TO THE NORTHEAST. TRACK SPEEDS ARE EXPECTED TO PICK UP IN THE NEAR-TERM BEFORE SLOWING ONCE AGAIN AS THE SYSTEM APPROACHES THE RIDGE AXIS AROUND TAU 48. AFTER TAU 48, THE SYSTEM TURNS NORTHEASTWARD AND RAPIDLY ACCELERATES ALONG THE TIGHT GRADIENT BETWEEN THE STR TO THE EAST AND AN APPROACHING MID-LATITUDE TROUGH MOVING OVER JAPAN. THE CURRENT FORECAST TRACK KEEPS TS 19W OFFSHORE BUT DOES MOVE THE TRACK A BIT CLOSER TO JAPAN. WITH THIS MODEL RUN, THE ECMWF BRINGS TS 19W MUCH CLOSER TO EASTERN HONSHU, PASSING JUST 30NM OFFSHORE, BROUGHT ON BY A CHANGE IN THE PLACEMENT OF THE STR TO THE EAST. THE GFS KEEPS THE RIDGE CENTERED FURTHER EAST, NEAR 155E, WITH A SOUTHWEST TO NORTHEAST AXIS ON THE WEST SIDE. THE ECMWF MEANWHILE CENTERS THE RIDGE AROUND 145E OR SO, WITH A MORE NORTH TO SOUTH AXIS ON THE WEST SIDE. IN TERMS OF INTENSITY, THE SYSTEM IS STILL EXPECTED TO WEAKEN SLIGHTLY IN THE NEXT 12 HOURS AS THE TUTT-CELL MOVES INTO ITS MOST UNFAVORABLE POSITION. BUT AS ALREADY NOTED, IT IS WEAKENING AND STRETCHING, AND WILL BE WEST OF TS 19W OR OTHERWISE WEAKENED ENOUGH TO LIMIT ITS INFLUENCE WITHIN THE NEXT 24 HOURS. AT THAT POINT, A POLEWARD OUTFLOW CHANNEL WILL OPEN UP, SHEAR WILL SLACKEN AND TS 19W WILL START TO INTENSIFY QUICKLY. THE FORECAST SHOWS THE PEAK OCCURRING AT TAU 72, HOWEVER, THE ACTUAL PEAK IS LIKELY TO OCCUR BETWEEN TAU 72 AND TAU 96 WITH A PEAK BETWEEN 70-80 KNOTS. BUT IMMEDIATELY AFTER REACHING ITS PEAK, RAPIDLY INCREASING SHEAR WILL TAKE ITS TOLL AND THE SYSTEM WILL BEGIN TO RAPIDLY WEAKEN BY TAU 96 WHILE ALSO BEGINNING EXTRATROPICAL TRANSITION (ETT). FULL TRANSITION TO AN EXTRATROPICAL LOW PRESSURE AREA IS EXPECTED NO LATER THAN TAU 120. MODEL DISCUSSION: TRACK GUIDANCE IS IN FAIRLY GOOD AGREEMENT THROUGH TAU 72, WITH A 290NM CROSS-TRACK SPREAD BY TAU 72. GFS CONTINUES TO TAKE THE INSIDE TRACK, WHILE NAVGEM AND GALWEM TAKE A WIDER TRACK TO THE WEST. AFTER TAU 72, AS DISCUSSED ABOVE, THE ECMWF INTERMEDIATE TRACKER SEPARATES FROM THE REMAINDER OF TEH GUIDANCE PACKAGE AND HEADS ALMOST DUE NORTH TO A POINT JUST EAST OF TOKYO. THE REMAINDER OF THE GUIDANCE CONTINUES WITH A RECURVE TRACK WITH A 360NM SPREAD BETWEEN THE GUIDANCE (EXCLUDING THE ECOI TRACKER WHICH ENDS AT TAU 96). ALONG-TRACK SPREAD HAS REDUCED SIGNIFICANTLY, WITH THE EXCEPTION OF THE NAVGEM WHICH LAGS OVER 1000NM BEHIND ALL THE OTHER TRACKERS BY TAU 120. THE JTWC TRACK IS SLOWER THAN THE CONSENSUS IN THE FIRST 24 HOURS TO ACCOUNT FOR THE RECENT TRACK SLOWDOWN, BUT OTHER REMAINS JUST INSIDE THE CONSENSUS MEAN TO TAU 72, THEN FOLLOWS THE CONSENSUS AT A SLIGHTLY FASTER PACE THROUGH TAU 120. INTENSITY GUIDANCE IS GOOD AGREEMENT ON THE NEAR-TERM WEAKENING, FOLLOWED BY STEADY INTENSIFICATION TO A PEAK BETWEEN 70 KNOTS AND 90 KNOTS, WHICH OCCURS AROUND TAU 84, FOLLOWED BY RAPID WEAKENING THEREAFTER. THE JTWC CLOSELY FOLLOWS THE CONSENSUS MEAN, IN LINE WITH THE HAFS-A, BUT WELL BELOW THE AGGRESSIVE COAMPS-TC SOLUTION. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN