WDPN32 PGTW 021500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 13W (THIRTEEN) WARNING NR 003// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 29.6N 139.6E INITIAL INTENSITY: 30 KTS GEOGRAPHIC REFERENCE: 342 NM SOUTH OF YOKOSUKA, JAPAN MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 16 KTS SIGNIFICANT WAVE HEIGHT: 14 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A HIGHLY ASYMMETRIC AND DISORGANIZED SYSTEM, POSITIONED ON THE NORTHERN SIDE OF AN ELONGATED BAND OF ELEVATED SOUTHWESTERLY FLOW EXTENDING FAR TO THE SOUTHWEST UP TO TS 12W. THE EIR LOOP ALSO DEPICTS A WELL-DEFINED AND EXPOSED LOW LEVEL CIRCULATION TO THE NORTHWEST OF THE ASSESSED INITIAL POSITION. THIS IS NOT THE PRIMARY LOW LEVEL CIRCULATION CENTER (LLCC) OF TD 13W, BUT RATHER REPRESENTS THE SECONDARY SPINNER WHICH WAS TRACKED MOVING RAPIDLY NORTHWARD TO THE EAST OF THE PRIMARY CIRCULATION OVER THE PAST 12 HOURS. IT IS CURRENTLY MOVING SOUTHEAST TOWARDS THE PRIMARY CIRCULATION. A 021107Z ASCAT-B PASS ALSO SHOWS THIS SETUP, WITH THE SECONDARY CIRCULATION WELL-DEFINED IN THE SCATTEROMETER PASS, BUT SURROUNDED BY RELATIVELY LIGHT (LESS THAN 20 KNOT) WINDS, WHILE THE AREA BEING TRACKED AS THE CENTER IS REFLECTED IN THE ASCAT PASS AS A SMALL WAVE FEATURE TO THE SOUTHEAST OF THE SECONDARY SPINNER. HIGHER WINDS UP TO 30-35 KNOTS ARE PRESENT CLOSE TO THE THIS REGION AND WRAPPING INTO THE CENTER, THOUGH THE WESTERN SIDE OF THE CIRCULATION DOES NOT APPEAR CLOSED AND WITH MUCH LIGHTER WINDS. FOR THE SAKE OF PERSISTENCE AND DUE TO THE FACT THAT THE OBVIOUS SPINNER IS MOVING SOUTHEAST TOWARDS THE CENTER OF TS 13W, THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE ON THE SOUTHEASTERN ROTATION IN THE ASCAT PASS. THE INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE ASCAT DATA AS WELL. ENVIRONMENTAL CONDITIONS REMAINS OVERALL FAVORABLE, WITH LOW VWS, WARM SSTS AND GOOD POLEWARD OUTFLOW. HOWEVER, THESE ARE OFFSET BY THE CLEAR ASYMMETRIES AND VORTEX MISALIGNMENT AS SEEN IN THE ASCAT DATA. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) CENTERED EAST OF IWO TO. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T1.5 - 25 KTS RJTD: T1.5 - 25 KTS KNES: T1.5 - 25 KTS CIMSS ADT: 31 KTS AT 021130Z CIMSS AIDT: 36 KTS AT 021130Z CIMSS D-PRINT: 26 KTS AT 021210Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 5-10 KTS SST: 28-29 CELSIUS OUTFLOW: MODERATE POLEWARD OTHER FACTORS: MULTIPLE VORTICES, WINDFIELD ASYMMETRIES ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH 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: TROPICAL DEPRESSION 13W IS FORECAST TO CONTINUE TRACKING NORTHEASTWARD FOR THE NEXT 24 HOURS ALONG THE WESTERN SIDE OF THE DEEP RIDGE TO THE EAST. AFTER TAU 24, THE TRACK WILL FLATTEN TO A MORE EASTWARD PATH AS THE RIDGE RAPIDLY SHIFTS WESTWARD. AFTER TAU 72 THE SYSTEM ONCE AGAIN TURNS NORTHEASTWARD AS A SEPARATE STR PUSHES WEST ACROSS THE DATELINE AND BECOMES THE DOMINANT STEERING INFLUENCE. TRACKS SPEEDS SLOW BRIEFLY AFTER TAU 72 DUE TO A WEAKENED STEERING GRADIENT AS THE STEERING INFLUENCE TRANSITIONS. IN TERMS OF INTENSITY, IT REMAINS HIGHLY UNLIKELY THAT TD 13W WILL BE ABLE TO INTENSIFY MUCH UNDER THE CURRENT MULTI-VORTEX, HIGHLY ASYMMETRIC CONDITIONS. IF, AS SOME OF THE HIGH-RESOLUTION MODELS SUGGEST, THE MULTIPLE VORTICES CAN MERGE AND ALIGN, THEN INTENSIFICATION CAN OCCUR. THE HAFS-A AND HWRF BOTH SUGGEST THIS VORTEX ALIGNMENT PROCESS WILL OCCUR WITHIN THE NEXT 12 TO 18 HOURS, THEREBY SETTING THE STAGE FOR INTENSIFICATION UNDER OTHERWISE FAVORABLE CONDITIONS OF LOW SOUTHERLY SHEAR AND WARM SSTS. HOWEVER, THERE WILL BE LIMITED TIME UNDER FAVORABLE SHEAR CONDITIONS, AND BY 72, THE COMBINATION OF INCREASED SHEAR AND DRY MID-LEVEL AIR INTRUSION WILL BEGIN A SLOW WEAKENING PHASE THAT WILL CONTINUE THROUGH THE END OF THE FORECAST. BY TAU 96, TD 13W WILL BEGIN EXTRATROPICAL TRANSITION (ETT) WITH COMPLETION OF ETT BY TAU 120. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE REMAINS IN TIGHT AGREEMENT THROUGH THE ENTIRE FORECAST PERIOD. CROSS-TRACK SPREAD AT TAU 72 IS JUST 110NM, OPENING TO 120NM BY TAU 120. ALONG-TRACK SPEED INCREASES MODESTLY AFTER TAU 96 AS THE SYSTEM UNDERGOES ETT. THE JTWC FORECAST IS POSITIONED ON THE NORTHERN EDGE OF THE GUIDANCE ENVELOPE, NEAR THE ECMWF TRACK SOLUTION THROUGH TAU 72, THEN CLOSE TO THE CONSENSUS MEAN THEREAFTER. INTENSITY GUIDANCE IS MIXED, WITH THE COTC INDICATING STEADY WEAKENING FROM THE START, WHILE THE REMAINDER OF THE GUIDANCE PACKAGE SHOWS STEADY INTENSITY FOR THE FIRST 12 HOURS, FOLLOWED BY STEADY INTENSIFICATION TO A PEAK BETWEEN 35-45 KNOTS BY TAU 48 THEN WEAKENING THROUGH THE END OF THE FORECAST. THE HWRF IS SLIGHTLY MORE AGGRESSIVE, PEAKING AT 43 KNOTS BY TAU 12 THEN MAINTAINING UNTIL TAU 72. THE JTWC FORECAST 5-10 KNOTS ABOVE THE CONSENSUS MEAN AND ROUGHLY CONSISTENT WITH THE DECAY-SHIPS GUIDANCE. FORECAST CONFIDENCE: TRACK 00-72 HR: HIGH TRACK 72-120 HR: HIGH INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN