WDPN33 PGTW 122100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 16W (SIXTEEN) WARNING NR 001// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 21.7N 138.5E INITIAL INTENSITY: 25 KTS GEOGRAPHIC REFERENCE: 242 NM SOUTHWEST OF IWO TO MOVEMENT PAST 6 HOURS: EASTWARD AT 03 KTS SIGNIFICANT WAVE HEIGHT: 12 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A RAGGED AND STILL SOMEWHAT DISORGANIZED CIRCULATION WITH POCKETS OF FLARING CONVECTION FIRING AND DISSIPATING ON THE PERIPHERY OF A PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC). THE SYSTEM IS VERY BROAD, WITH AN OUTERMOST CLOSED ISOBAR RADIUS OF 250NM, BRINGING IT CLOSE TO THRESHOLD OF A MONSOON DEPRESSION. EARLIER SCATTEROMETER DATA INDICATED THE SYSTEM HAS SLID SOUTHWARD OVER THE PREVIOUS 12 HOURS AND BUT NOW HAS COME TO A HALT AND BEGUN DRIFTING BACK TO THE EAST. A 121846Z SSMIS COLORIZED 89GHZ MICROWAVE IMAGE SHOWED DISORGANIZED AND FRAGMENTED BANDING FEATURES, PARTICULARLY ON THE NORTHERN SIDE OF THE LLCC, WRAPPING INTO THE ILL-DEFINED CENTER, AND LENT MEDIUM CONFIDENCE TO THE INITIAL POSITION. MEANWHILE, THE SSMIS WINDSPEED ESTIMATE SHOWED PATCHES OF 25-30 KNOTS WINDS, MOSTLY LIMITED TO THE EAST AND SOUTHEAST SECTORS, WHICH ALIGNS WELL WITH A 121130Z ASCAT-B PASS SHOWING A BROAD REGION OF 20-25 KNOT WINDS TO THE EAST OF THE LLCC. ANALYSIS REVEALS AN OVERALL MARGINAL ENVIRONMENT WITH FAVORABLE SHEAR AND SSTS BEING OFFSET BY WEAK OUTFLOW CONDITIONS ALOFT. THE STEERING PATTERN IS WEAK WITH THE SYSTEM EMBEDDED IN A LARGE UPPER-LEVEL TROUGH CONNECTING WITH TY 14W TO THE WEST, AND A LARGE SUBTROPICAL RIDGE (STR) TO THE NORTH AND NEAR EQUATORIAL RIDGE (NER) TO THE SOUTHEAST. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: WEAK STEERING ENVIRONMENT BETWEEN NER TO THE SOUTHEAST AND STR TO THE NORTH AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS RJTD: T1.5 - 25 KTS KNES: T1.0 - 25 KTS FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 0-5 KTS SST: 29-30 CELSIUS OUTFLOW: WEAK RADIAL ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: NOT APPLICABLE 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY. FORECAST DISCUSSION: THE SYSTEM CURRENTLY LIES WITHIN A COMPLEX STEERING PATTERN DEFINED BY A NER TO THE SOUTH AND A STR TO THE NORTH, AND ITSELF BEING EMBEDDED WITHIN A LARGE, NEARLY MONSOON GYRE-SIZED TROUGH WHICH CONNECTS WITH TY 14W TO THE WEST. THE STRONGEST GRADIENT HOWEVER IS CURRENTLY ON THE SOUTHERN SIDE OF THE SYSTEM AND THUS THE PRIMARY STEERING INFLUENCE IS THE NER TO THE SOUTH. HENCE THE SYSTEM IS FORECAST TO DRIFT SLOWLY EAST-NORTHEASTWARD THROUGH THE NEXT 24 TO 36 HOURS. AROUND TAU 36 THE NER WILL WEAKEN AND FLATTEN OUT, REDUCING THE GRADIENT FORCE ON THE SOUTHERN SIDE OF THE SYSTEM AND AS THE PRIMARY STEERING MECHANISM SHIFTS TO THE STR OVER JAPAN, TD 16W WILL TURN SHARPLY ONTO A WEST-NORTHWEST HEADING BY TAU 48. ONCE ESTABLISHED ON THE NEW COURSE, THE SYSTEM IS EXPECTED TO SPEED UP AS IT TRACKS ALONG THE SOUTHWESTERN PERIPHERY OF THE DEEP STR. THE APPROACH OF A MID-LATITUDE TROUGH FROM THE WEST WILL BEGIN TO ERODE THE RIDGE BY TAU 96, ALLOWING FOR THE SYSTEM TO BEGIN TO RECURVE POLEWARD AT THAT TIME. WHILE SHEAR IS EXPECTED TO REMAIN LOW THROUGH MOST OF THE FORECAST PERIOD, THIS IS PRIMARILY DUE TO THE FACT THAT THE SYSTEM DOES NOT ESTABLISH A GOOD OUTFLOW CHANNEL FOR AT LEAST THE FIRST 48 HOURS, WHICH WILL KEEP A LID ON THE PACE OF CONSOLIDATION AND INTENSIFICATION THROUGH THAT POINT. BY TAU 48, MODELS SHOW THE FIRST HINTS OF AN UPPER-LEVEL POINT SOURCE AND BY TAU 72 SHOW ESTABLISHMENT OF A POLEWARD OUTFLOW CHANNEL, WHICH WILL ALLOW FOR A MORE RAPID PACE OF INTENSIFICATION, TO A PEAK OF 90 KNOTS BY TAU 96. THEREAFTER THE SYSTEM STALLS OUT AT 90 KNOTS AS IT GETS CUT OFF FROM THE POLEWARD OUTFLOW CHANNEL AND FACES CONVERGENT FLOW ALOFT EMANATING FROM A STRONG ANTI-CYCLONE AT 200MB POSITIONED TO THE NORTHEAST. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN FAIRLY GOOD AGREEMENT OVERALL, WITH ALL CONSENSUS MEMBERS AGREEING ON THE SHORT-TERM DRIFT TO THE EAST-NORTHEAST FOLLOWED BY THE SHARP TURN TO THE WEST BETWEEN TAU 24 AND 48. GFS IS THE OUTLIER UP TO TAU 48, SHOWING A WIDER MORE GRADUAL TURN AND EXTENDING EAST OUT TO NEAR 141E BEFORE TURNING WEST. THE REMAINDER OF THE PACK CONCURS ON A TURN AROUND 140E OR A BIT FURTHER WEST, LEADING TO A SPREAD IN THE GUIDANCE OF ABOUT 100NM AT THE TURNING POINT. ONCE FIRMLY ON THE WEST-NORTHWEST TRACK, THE CROSS-TRACK SPREAD ACTUALLY DECREASES TO 90NM BY TAU 72, THOUGH THE GFS LAGS BEHIND THE PACK DUE TO IT'S FURTHER EAST STARTING POINT. AFTER TAU 72, THE DETERMINISTIC TRACKERS QUICKLY SPREAD TO 230NM WITH THE ECMWF AND GALWEM ON THE LEFT AND GFS ENSEMBLE MEAN AND NAVGEM ON THE RIGHT OF THE ENVELOPE. ENSEMBLE GUIDANCE SHOWS A HIGH DEGREE OF UNCERTAINTY, WITH THE ECENS INDICATING A STRONGER RIDGE THAT FIGHTS OFF THE TROUGH APPROACHING FROM THE WEST AND REMAINS IN PLACE TO THE NORTH, WITH A RESULTANT FLATTER TRACK, JUST NORTH OF OKINAWA. THE GEFS MEANWHILE ERODES THE RIDGE MUCH FASTER, ALLOWING FOR A SHARP RECURVE TOWARDS SOUTHERN KYUSHU, THOUGH SOME MEMBERS DO AGREE WITH THE ECENS MEAN. THE JTWC TRACK LIES JUST EAST AND NORTH OF THE CONSENSUS MEAN, HEDGED TOWARDS THE GFS ENSEMBLE MEAN WITH LOW CONFIDENCE THROUGHOUT THE FORECAST DUE TO THE UNCERTAINTIES IN THE NEAR-TERM ERRATIC MOTION AND LONGER TERM ENSEMBLE SPREAD. INTENSITY GUIDANCE IS IN GOOD AGREEMENT ON A RATHER SLOW INTENSIFICATION TREND THROUGH TAU 48 FOLLOWED BY SHARPER INTENSIFICATION THEREAFTER. HWRF AND DECAY-SHIPS (GFS) ARE ON THE HIGHER END OF THE ENVELOPE AFTER TAU 72, AND PEAK THE SYSTEM AT 105 KNOTS. THE JTWC FORECAST LIES SLIGHTLY BELOW THE CONSENSUS TO TAU 48 THEN MATCHES IT THROUGH THE REMAINDER OF THE PERIOD. FORECAST CONFIDENCE: TRACK 0 - 72 HR: LOW TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN