WDPN33 PGTW 121500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 08W (EIGHT) WARNING NR 001// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 23.6N 136.7E INITIAL INTENSITY: 25 KTS GEOGRAPHIC REFERENCE: 719 NM SOUTH-SOUTHWEST OF YOKOSUKA, JAPAN MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 07 KTS SIGNIFICANT WAVE HEIGHT: 10 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS FLARING CONVECTION AROUND A STILL SOMEWHAT DISORGANIZED LOW LEVEL CIRCULATION CENTER (LLCC). THE CONVECTION AT PRESENT IS STARTING TO ORGANIZE INTO A BAND ON THE WESTERN SIDE OF THE CIRCULATION AND FLARING IN POCKETS ON THE EASTERN SIDE, BUT AS OF YET NOT WRAPPING INTO A DEFINED CENTER. A PARTIAL 121058Z ASCAT-B PASS SHOWED CYCLONICALLY CURVED WIND BARBS ON THE FAR WESTERN PERIPHERY OF THE CIRCULATION, WITH WINDS UP TO 25 KNOTS. AN EARLIER SCATTEROMETER PASS SHOWED WINDS UP TO 20 KNOTS IN A BAND TO THE NORTH, AND UP TO 30 KNOTS IN STRONG GRADIENT FLOW ALONG THE SOUTHEASTERN FLANK OF THE CIRCULATION. A 120852Z TROPICS 91GHZ IMAGE SHOWED A SMALL AND DEFINED LLCC WITH DEEP CONVECTION PRIMARILY LIMITED TO THE SOUTHERN PERIPHERY. THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE PARTIAL ASCAT AND EARLIER SCATTEROMETER PASSES AND GENERAL AGREEMENT BETWEEN THE PGTW AND KNES FIX POSITIONS. THE INITIAL INTENSITY OF 25 KNOTS IS ASSESSED WITH MEDIUM CONFIDENCE, BASED ON A BLEND OF THE AGENCY DVORAK ESTIMATES BETWEEN T1.0 (PGTW) AND T2.0 (KNES), AS WELL AS AN EARLY CIMSS DPRINT ESTIMATE OF 28 KNOTS, ALONG WITH THE AFOREMENTIONED SCATTEROMETER DATA. ANALYSIS REVEALS A FAVORABLE ENVIRONMENT, CHARACTERIZED BY VERY WARM SSTS, RELATIVELY HIGH OHC, LOW (5-15 KTS) VWS AND GOOD POLEWARD OUTFLOW INTO A TUTT-CELL POSITIONED TO THE NORTHWEST AND MODERATE EQUATORWARD OUTFLOW PROVIDED BY A WEAK ANTICYCLONE JUST EAST OF THE SYSTEM. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF AN EXTENSION OF THE SUBTROPICAL RIDGE (STR) EXTENDING FROM LUZON, NORTHEAST ACROSS THE MARIANAS ISLANDS. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T1.0 - 25 KTS RJTD: T1.5 - 25 KTS KNES: T2.0 - 30 KTS CIMSS DPRINT: 28 KTS AT 121200Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 30-31 CELSIUS OUTFLOW: STRONG POLEWARD AND EQUATORWARD 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: TROPICAL DEPRESSION (TD) 08W (EIGHT) HAS STEADILY BECOME BETTER ORGANIZED OVER THE LAST DAY, BUT REMAINS HIGHLY ASYMMETRIC IN TERMS OF THE LOW-LEVEL WIND FIELD, AND LIKELY AT LEAST TWO LOW-LEVEL VORTICES LURKING UNDER THE CONVECTION AND CONVECTIVE BLOWOFF. OVER THE NEXT 24 TO 36 HOURS, THE EXTENSION OF THE STR CURRENTLY LAYING ACROSS THE MARIANAS IS EXPECTED TO CUT OFF INTO A DEEP-LAYER ANTICYCLONE NEAR 20N 145E. AS THE GRADIENT TIGHTENS IN RESPONSE TO THE BUILDING OF THE RIDGE, TD 08W WILL TRACK NORTHEASTWARD UNTIL TAU 36. AT THIS POINT, TD 08W WILL MOVE INTO A SOMEWHAT WEAKER STEERING PATTERN, SLOWING DOWN AS IT DOES SO. BY TAU 36 A SIGNIFICANT PATTERN SHIFT BEGINS TO EMERGE, WITH THE STRONG STR POSITIONED AT AN ANOMALOUSLY HIGH LATITUDE OF 40N, STARTS TO MOVE SOUTHWARD WHILE BUILDING. THIS STR QUICKLY BECOMES THE DOMINANT STEERING INFLUENCE FOR TD 08W, WHICH WILL TURN NORTHWARD AND ACCELERATE AFTER TAU 36 ALONG THE WESTERN PERIPHERY OF THIS RIDGE. TD 08W IS EXPECTED TO REACH THE RIDGE AXIS JUST SOUTH OF TOKYO, AND SHORTLY AFTER TAU 96 WILL BEGIN TO TURN NORTHEASTWARD AS IT ROUNDS THE RIDGE AXIS. IN TERMS OF INTENSITY, TD 08W CURRENTLY SITS IN A FAVORABLE ENVIRONMENT, TAPPING INTO ENHANCED OUTFLOW INTO A TUTT-CELL POSITIONED TO THE NORTHWEST. OVER THE NEXT 12-24 HOURS THIS OUTFLOW CHANNEL IS EXPECTED TO WEAKEN AND DISAPPEAR, AS THE TUTT-CELL MOVES WEST AND TD 08W MOVES NORTHEASTWARD. HOWEVER, SHEAR IS EXPECTED TO REMAIN LOW AND THIS SHOULD ALLOW FOR THE SYSTEM TO SYMMETRIZE, SETTING THE STAGE FOR FUTURE INTENSIFICATION. BY TAU 24, AN UPPER-LEVEL ANTICYCLONE IS EXPECTED TO DEVELOP OVER TOP OF THE SYSTEM, WHICH FUELS A SLIGHTLY FASTER RATE OF INTENSIFICATION UP TO 50 KTS BY TAU 36. AT THIS POINT, ANOTHER TUTT-CELL IS FORECAST TO DEVELOP TO THE NORTH OF THE SYSTEM, GREATLY ENHANCING UPPER-LEVEL OUTFLOW. BY TAU 72, A LARGER UPPER-LEVEL ANTICYCLONE DEVELOPS EAST OF THE SYSTEM, GREATLY ENHANCING THE ALREADY STRONG OUTFLOW, KICKING OFF A PERIOD OF RAPID INTENSIFICATION AS IT APPROACHES JAPAN. PEAK INTENSITY AROUND 100 KNOTS IS EXPECTED AS THE SYSTEM REACHES THE RIDGE AXIS NEAR TAU 96, WITH RELATIVELY RAPID WEAKENING THEREAFTER AS THE SYSTEM MOVES OVER COOLER WATERS AND MODERATELY ELEVATED SHEAR. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GOOD AGREEMENT ON THE OVERALL SCENARIO, WITH A 150NM SPREAD AT TAU 48 BETWEEN THE UKMET ENSEMBLE MEAN ON THE FAR LEFT AND GFS ON THE RIGHT. THE UKMET ENSEMBLE MEAN AND THE NAVGEM ARE SIGNIFICANT OUTLIERS TO THE WEST AFTER TAU 36 AND ARE DISCOUNTED FROM THE CONSENSUS AS A RESULT. THE REMAINDER OF THE GUIDANCE MEMBERS HAVE A SPREAD OF JUST 80NM AT TAU 48. CROSS-TRACK SPREAD OPENS UP TO 150NM AT CPA TO YOKOSUKA (TAU 96), WITH THE JGSM ON THE WEST SIDE AND THE GFS ENSEMBLE MEAN ON THE EAST SIDE, WELL OUT TO SEA. BY TAU 120, CROSS-TRACK SPREAD REMAINS ROUGHLY CONSISTENT, BUT ALONG-TRACK SPREAD BEGINS TO INCREASE AFTER THE SYSTEM ROUNDS THE RIDGE. THE JTWC TRACK LIES ON THE EASTERN EDGE OF THE GUIDANCE PACKAGE TO TAU 48, THEN LIES JUST EAST OF THE CONSENSUS MEAN, CLOSE TO THE GFS, THROUGH THE REMAINDER OF THE FORECAST PERIOD. ENSEMBLE GUIDANCE ALSO IN GOOD AGREEMENT ON THE OVERALL SCENARIO WITH A MODERATE AMOUNT OF SPREAD IN MEMBERS. TRACK CONFIDENCE IS HIGH THROUGH TAU 48, AND MEDIUM THEREAFTER. INTENSITY GUIDANCE AGREES THAT THE SYSTEM WILL INTENSIFY BUT DIFFERS ON THE PACE AND PEAK. THE CTR1 RI TRACKER IS THE MOST AGGRESSIVE, PEAKING AT 110 KNOTS AT TAU 84, THE HAFS-A ALSO PEAKS AT 110 KTS AT TAU 96. THE REMAINDER OF THE GUIDANCE PEAKS AT OR BELOW 80 KNOTS. NO RI AIDS OTHER THAN CTR1 ARE TRIGGERED BUT RI PROBABILITIES ARE RUNNING AT 30-40 PERCENT. THE JTWC FORECAST TRACKS THE MEAN TO TAU 48, THEN SHIFTS TO THE HIGHER HAFS-A TREND, THOUGH REMAINS ABOUT 10 KNOTS LOWER. CONFIDENCE IS MEDIUM THROUGHOUT DUE TO THE UNCERTAINTIES SURROUNDING THE POSSIBILITY OF RI. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN