WDPN31 PGTW 232100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 08W (EIGHT) WARNING NR 004// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 16.6N 149.7E INITIAL INTENSITY: 25 KTS GEOGRAPHIC REFERENCE: 328 NM EAST-NORTHEAST OF ANDERSEN AFB MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 04 KTS SIGNIFICANT WAVE HEIGHT: 12 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A HIGHLY ASYMMETRIC LOW LEVEL CIRCULATION CENTER (LLCC), WHICH IS PARTIALLY EXPOSED TO THE WEST OF AN AREA OF DIURNALLY FLARING CONVECTION. A 231758Z SSMIS 91GHZ MICROWAVE IMAGE SHOWED THE WELL-DEFINED LLCC AT THE WESTERN POINT OF AN AREA OF LINEAR, DISORGANIZED CONVECTION WHICH CONTINUES TO EXPAND RADIALLY IN THE EIR. CIRA ADVECTED LAYER PRECIPITABLE WATER, HIGH RESOLUTION MODEL CROSS-SECTIONS, AND REGIONAL UPPER-AIR SOUNDINGS, INDICATE A WEDGE OF DRY AIR BETWEEN ROUGHLY 850MB-500MB, IN PLACE ON THE WESTERN SIDE OF THE SYSTEM. CIMSS UPPER-LEVEL ANALYSIS, ANIMATED WATER VAPOR IMAGERY AND JTWC HAND-ANALYSIS SHOWS A SHARP 200MB TROUGH LIES JUST WEST OF THE LLCC, PLACING THE LLCC ALONG THE TROUGH AXIS AND THE EASTERN EXTENT OF THE CIRCULATION UNDER THE DIFFLUENT REGION, FEEDING THE FLARE-UP OF CONVECTION THERE. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE PARTIALLY EXPOSED LLCC IN THE EIR. THE INITIAL INTENSITY HAS BEEN ADJUSTED SLIGHTLY LOWER, TO 25 KNOTS, WITH HIGH CONFIDENCE. THIS ASSESSMENT IS BASED PRIMARILY ON TWO ASCAT PASSES (1049Z AND 1141Z), BOTH OF WHICH INDICATED A VERY WEAK SURFACE WIND FIELD, WITH ONLY ISOLATED POCKETS OF 25 KNOT WINDS IN THE NORTHERN PORTION OF THE CIRCULATION. AGENCY FIXES ARE BETWEEN T1.0 TO T2.0, WHILE THE CIMSS DPRINT AND DMINT ARE 25-27 KNOTS RESPECTIVELY. THE SYSTEM IS CURRENTLY DRIFTING TO THE SOUTHWEST UNDER A WEAK STEERING INFLUENCE. ENVIRONMENTAL CONDITIONS ARE MARGINAL, WITH LOW SHEAR AND WARM SSTS BEING OFFSET SLIGHTLY BY CURRENTLY MARGINAL OUTFLOW AND THE PREVIOUSLY MENTIONED DRY AIR. THE ASCAT ALSO REVEALED THE VERY BROAD NATURE OF THE WIND FIELD AND GLOBAL MODEL FIELDS SHOW A RADIUS OF THE OUTERMOST ISOBAR (ROMCI) EXCEEDING 340NM, MAKING THIS AN EXTREMELY LARGE, MONSOON DEPRESSION-LIKE SYSTEM. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: WEAK STEERING ENVIRONMENT BETWEEN A STRONG NEAR-EQUATORIAL RIDGE (NER) TO THE EAST AND A SUBTROPICAL RIDGE (STR) COMPLEX TO THE WEST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.0 - 30 KTS RJTD: T1.0 - 25 KTS KNES: T2.0 - 30 KTS CIMSS ADT: 34 KTS AT 231730Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 5-10 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE POLEWARD OTHER FACTORS: VERY DRY AIR OVER THE WESTERN PORTION OF THE CIRCULATION. 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: TD 08W (EIGHT) PRESENTS A VERY COMPLEX FORECAST SCENARIO, EXHIBITING FEATURES OF A VERY LARGE TROPICAL DEPRESSION, OR MONSOON DEPRESSION. MODELS ARE THUS HAVING A VERY HARD TIME HANDLING THE FORECAST, WITH THE TRACKERS JUMPING VORTICES AND VARYING WIDELY IN BOTH ALONG AND CROSS-TRACK MOTION VECTORS. THE OVERALL STEERING PATTERN LOOKS TO FIRM UP OVER THE NEXT FEW HOURS, WITH THE NER TO THE EAST BECOMING THE MORE DOMINANT FEATURE. TD 08W IS FORECAST TO CEASE TRACKING WESTWARD, TURN SOUTH AND THEN LOOP BACK TO THE NORTHEAST OVER THE NEXT 24 TO 36 HOURS. TRACK SPEEDS WILL PICK UP STEADILY AFTER IT MAKES THE TURN TO THE NORTHEAST. AT THE SAME TIME ALL THIS IS OCCURRING, THE GLOBAL MODELS, MOSTLY GFS BUT TO A LESSER EXTENT THE ECMWF, INDICATE AN AREA OF VORTICITY SPINNING UP TO THE EAST-NORTHEAST OF TD 08W, AND SPINNING UP INTO A SEPARATE AND DISTINCT CIRCULATION CENTER. THIS SCENARIO IS NOT UNEXPECTED WHEN VIEWING TD 08W AS THE CENTER OF A BROAD GYRE-LIKE SYSTEM. THE MODELS THEN JUMP TO THE NEW CENTER OR MERGE THE TWO INTO ONE SYSTEM. THE HAFS-A APPEARS TO BE AN OUTLIER HERE, IN THAT IT KEEPS THESE TWO AREAS SEPARATE THROUGH THE FORECAST PERIOD. REGARDLESS, THE TRACK GUIDANCE DRAMATICALLY ACCELERATES AFTER TAU 48, AS THE STR TO THE NORTH BECOMES THE DOMINATE STEERING MECHANISM. THE CURRENT FORECAST IS VERY MUCH A BLEND OF THE WIDELY DIVERGENT GUIDANCE, TRACKING FAIRLY CLOSE TO THE LATEST ECMWF RUN, BUT WELL SHORT OF THE MUCH FASTER US MODEL GUIDANCE. EVEN STILL, THERE IS A CHANGE OF 260NM IN THE TAU 120 POSITION FROM THE PREVIOUS FORECAST. IN TERMS OF INTENSITY, THE GUIDANCE IS SPREAD ACROSS A WIND MARGIN, WITH PEAK INTENSITIES SPREAD FROM 35 KNOTS TO 100 KNOTS, INCLUDING SOME RAPID INTENSIFICATION (RI) GUIDANCE. IN VIEW OF THE VERY DRY AIR, WHICH IS FORECAST TO PERSIST THROUGH THE SYSTEMS LIFE, LARGE CIRCULATION CENTER AND THE FACT THAT SHEAR IS ANTICIPATED TO DRAMATICALLY AND SHARPLY INCREASE AFTER TAU 48, THE MORE AGGRESSIVE OUTCOMES SEEM UNLIKELY. THE SYSTEM IS FORECAST TO SLOWLY CONSOLIDATE AND INTENSIFY, PEAKING AT 55 KNOTS AROUND TAU 72, BEFORE WEAKENING ONCE MORE AS IT TRACKS NORTH UNDER 200MB WINDS APPROACHING 65 KNOTS. MODEL DISCUSSION: AS GENERALLY OUTLINED ABOVE, DETERMINISTIC TRACK GUIDANCE IS IN POOR AGREEMENT, PARTICULARLY IN THE ALONG-TRACK SPREAD AFTER TAU 48. IN THE NEAR-TERM, THE GUIDANCE IS ACTUALLY IN FAIRLY DECENT AGREEMENT THAT THE SYSTEM WILL LOOP SOUTH AND THEN GRADUALLY TURN NORTHWARD BY TAU 48. HOWEVER, DUE TO THE 180DEG CHANGE IN TRACK MOTION FROM TAU 00 TO TAU 24, THE SYSTEM NOW TRACKS MUCH FURTHER EAST THAN THE PREVIOUS FORECAST BUT THE JTWC FORECAST IS IN GOOD AGREEMENT WITH THE CONSENSUS MEAN AND ALL BUT THE GFS, WHICH TRACKS THE SYSTEM EVEN FURTHER EAST. AFTER TAU 72, THE JTWC FORECAST DEVIATES FROM THE CONSENSUS FAIRLY SIGNIFICANTLY, HOLDING BACK ON THE FORWARD MOTION FROM THE VERY FAST CONSENSUS MEAN AND MORE CLOSELY TRACKING THE ECMWF. UNCERTAINTY IS VERY HIGH, PARTICULARLY AFTER TAU 48, WITH MODEL SPREAD INCREASING TO NEARLY 800NM (ALONG-TRACK) BY TAU 120. IN A SIMILAR MANNER, THERE IS VERY LOW CONFIDENCE IN THE INTENSITY FORECAST, WITH A VERY LARGE SPREAD IN POTENTIAL PEAK INTENSITIES. AS DISCUSSED ABOVE, THE JTWC FORECAST IS ON THE LOWER END OF THE GUIDANCE, BUT LIES FAIRLY CLOSE TO THE CONSENSUS MEAN. FORECAST CONFIDENCE: TRACK 0 - 72 HR: LOW TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: LOW INTENSITY 72-120 HR: LOW// NNNN