WDPN31 PGTW 252100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 19W (NINETEEN) WARNING NR 001// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 22.4N 145.0E INITIAL INTENSITY: 30 KTS GEOGRAPHIC REFERENCE: 249 NM SOUTHEAST OF IWO TO MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 12 KTS SIGNIFICANT WAVE HEIGHT: 13 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL DEPRESSION (TD) 19W HAS SLOWLY CONSOLIDATED OVER THE PAST 12 HOURS AROUND A BROAD LOW-LEVEL CIRCULATION (LLC). ALTHOUGH A 251200Z ASCAT-B IMAGE SHOWED A SHARP TROUGH WITH NO CLOSED CIRCULATION, ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS IMPROVED CONVECTIVE BANDING ALONG THE SOUTHERN AND EASTERN PERIPHERIES. CONSEQUENTLY, DVORAK ESTIMATES HAVE INCREASED TO T1.5 (25 KNOTS) FROM ALL AGENCIES. THE ASCAT-B IMAGE INDICATED A SWATH OF 30-35 KNOT WINDS ASSOCIATED WITH THE CONVECTIVE BANDING BUT LESS THAN 20 KNOTS ELSEWHERE THUS THE INITIAL INTENSITY IS ASSESSED SLIGHTLY HIGHER THAN THE DVORAK INTENSITY ESTIMATES. THE 251157Z ASCAT-B WINDSPEED IMAGE SHOWS A WIND MINIMUM SUGGESTING A DEVELOPING LOW- LEVEL CIRCULATION CENTER AND A 251640Z ATMS 88.2GHZ MICROWAVE IMAGE SHOWS A WEAKLY-DEFINED LLCC ALONG THE WESTERN EDGE OF THE CURVED BAND, WHICH SUPPORTS THE INITIAL POSITION WITH MEDIUM CONFIDENCE. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: COMBINED STEERING INFLUENCE WITH A DEEP- LAYERED SUBTROPICAL RIDGE (STR) POSITIONED TO THE EAST AND A WEAK STR TO THE NORTH. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T1.5 - 25 KTS RJTD: T1.5 - 25 KTS KNES: T1.5 - 25 KTS FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 28-29 CELSIUS OUTFLOW: STRONG POLEWARD AND EQUATORWARD ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: HIGH INITIAL WIND RADII: NOT APPLICABLE 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY. FORECAST DISCUSSION: TD 19W IS FORECAST TO TRACK GENERALLY NORTHWESTWARD THROUGH TAU 24 WITHIN THE COMBINED STEERING INFLUENCE OF THE BROAD STR TO THE EAST AND THE WEAK STR POSITIONED TO THE NORTH. AFTER TAU 24, A DEEP MIDLATITUDE SHORTWAVE TROUGH WILL APPROACH CENTRAL JAPAN AND WEAKEN THE STR TO THE NORTH ALLOWING THE SYSTEM TO TURN POLEWARD THROUGH TAU 36 THEN RECURVE NORTHEASTWARD ALONG THE NORTHWESTERN FLANK OF THE RE-ORIENTED STR TO THE SOUTHEAST. BY TAU 48, TD 19W WILL BEGIN EXTRA-TROPICAL TRANSITION (ETT) AS IT INTERACTS WITH THE MIDLATITUDE WESTERLIES AND BAROCLINIC ZONE. THE SYSTEM WILL COMPLETE ETT BY TAU 72 AS IT GAINS FRONTAL CHARACTERISTICS AND BECOMES EMBEDDED WITHIN THE MIDLATITUDE WESTERLIES. TD 19W SHOULD INTENSIFY STEADILY THROUGH TAU 48 UNDER FAVORABLE CONDITIONS TO A PEAK OF 70 KNOTS. ATER TAU 48, COOLER SEA SURFACE TEMPERATURE VALUES (25-26C) AND STRONG VERTICAL WIND SHEAR WILL WEAKEN THE SYSTEM. MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN TIGHT AGREEMENT WITH A SPREAD OF LESS THAN 80NM THROUGH THE FORECAST PERIOD LENDING HIGH CONFIDENCE TO THE JTWC FORECAST TRACK. ADDITIONALLY, THE 250600Z ECMWF ENSEMBLE (EPS) AND 251200Z GFS ENSEMBLE (GEFS) ARE IN GOOD AGREEMENT SUPPORTING THE JTWC FORECAST TRACK. THE 251200Z COAMPS-TC ENSEMBLE INDICATES A LOW PROBABILITY (10 TO 30 PERCENT) FOR RAPID INTENSIFICATION PEAKING IN THE TAU 36 TO TAU 60 PERIOD. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH INTENSITY 0 - 72 HR: MEDIUM// NNNN