WDPN31 PGTW 240300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 08W (EIGHT) WARNING NR 005// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 16.5N 150.0E INITIAL INTENSITY: 25 KTS GEOGRAPHIC REFERENCE: 340 NM EAST-NORTHEAST OF ANDERSEN AFB MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 03 KTS SIGNIFICANT WAVE HEIGHT: 11 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: BASED ON THE MOST RECENT ASCAT PASS FROM 232319Z, TROPICAL DEPRESSION (TD) 08W (EIGHT) IS ACTUALLY A LARGE MONSOON DEPRESSION WITH A RADIUS OF MAXIMUM WINDS (RMW) EXCEEDING 150NM AND A RADIUS OF THE OUTERMOST ISOBAR (ROMCI) IN EXCESS OF 370NM. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THAT THE DEEP CONVECTION THAT HAD FLARED UP NEAR THE LOW LEVEL CIRCULATION CENTER (LLCC) DURING THE DIURNAL MAXIMUM HAS DISSIPATED, AND BEEN SHEARED OFF TO THE EAST, LEAVING A FULLY EXPOSED LLCC IN ITS WAKE. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC IN THE ANIMATED MSI AS WELL AS THE ASCAT-DERIVED POSITION BASED ON THE PREVIOUSLY DISCUSSED ASCAT PASS. THE INITIAL INTENSITY REMAINS SET AT 25 KNOTS WITH HIGH CONFIDENCE, BASED ON THE ASCAT DATA, AND WELL BELOW THE MAJORITY OF THE DVORAK-BASED INTENSITY ESTIMATES. CIMSS ATMOSPHERIC MOTION VECTORS (AMVS), AND ANIMATED WATER VAPOR IMAGERY ANALYSIS REVEALS A SHARP UPPER-LEVEL TROUGH WITH AN AXIS ON TOP OF OR VERY NEAR THE LLCC, WHICH IS INDUCING CONVERGENT FLOW OVER THE WESTERN SIDE OF THE ROTATION. THE EASTERN PORTION OF THE CIRCULATION HOWEVER, LIES UNDER THE BROAD DIFFLUENT SECTOR OF THE TROUGH, ENHANCING CONVECTION AND POLEWARD OUTFLOW IN THAT PORTION OF THE CIRCULATION. THUS THE ENVIRONMENT IS MARGINAL AT PRESENT, WITH ROBUST POLEWARD OUTFLOW OVER THE EASTERN PORTION OF THE SYSTEM AND WARM SSTS OFFSET BY CONVERGENT FLOW ON THE WEST SIDE AND DRY AIR ENTRAINMENT ON THE WESTERN PERIPHERY. THE LLCC LOOKS TO HAVE BECOME QUASI-STATIONARY IN A BROAD AND WEAK STEERING PATTERN, WHICH IS SETTING UP TO BECOME A MONSOON GYRE. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: BROAD AND WEAK STEERING PATTERN WITH NO CLEAR STEERING INFLUENCE. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.0 - 30 KTS RJTD: T1.5 - 25 KTS KNES: T2.5 - 35 KTS CIMSS ADT: 41 KTS AT 232340Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL VWS: 0-5 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE POLEWARD OTHER FACTORS: OUTFLOW IS CONSTRAINED TO THE EASTERN PORTION OF THE CIRCULATION; DRY CONVERGENT AIR ALONG THE WESTERN PORTION. ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH 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: WHILE THE ACTUAL LLCC ASSOCIATED WITH WHAT IS PROPERLY DESCRIBED AS MONSOON DEPRESSION 08W IS VERY SMALL, THE ENTIRETY OF THE CIRCULATION IS QUITE LARGE. THE CENTER IS TRAPPED WITHIN A VERY LARGE AND WEAK STEERING PATTERN, SETTING UP TO BECOME A MONSOON GYRE OVER THE NEXT DAY OR TWO. THUS, THE SYSTEM IS NOT EXPECTED TO MOVE MUCH THROUGH THE NEXT 12 TO 24 HOURS. TWO THINGS OCCUR AFTER TAU 24 WHICH WILL CHANGE THAT. FIRST, A LOW TO MID-LEVEL NEAR EQUATORIAL RIDGE (NER) WILL DEVELOP NEAR CHUUK AND SECOND, A NEW AREA OF VORTICITY IS FORECAST TO DEVELOP NEAR 22N 155E ON THE EASTERN PERIPHERY OF THE MONSOON DEPRESSION OR GYRE. THE COMBINATION OF THESE TWO OCCURRENCES WILL PUSH TD 08W ONTO A NORTHEASTERN TRACK BY TAU 36, PICKING UP A SIGNIFICANT HEAD OF STEAM AS IT DOES SO. BY TAU 48 OR SHORTLY THEREAFTER, TD 08W IS EXPECTED TO MERGE WITH THE SECONDARY CIRCULATION RAPIDLY DEVELOPING TO THE NORTHEAST, THUS THE VORTEX APPEARS TO JUMP RAPIDLY UP TO THE NEW CENTER. THEREAFTER THE STEERING INFLUENCE SHIFTS TO THE STRONG SUBTROPICAL RIDGE (STR) TO THE NORTH, AND TD 08W WILL RAPIDLY ACCELERATE TOWARDS THE NORTHWEST THROUGH TAU 96. THE SYSTEM SLOWS, AND TURNS MORE POLEWARD BY THE END OF THE FORECAST AS IT ROUNDS THE RIDGE AXIS. IN TERMS OF INTENSITY, THE FORECAST PRESENTS SIGNIFICANT CHALLENGES DUE TO THE BROAD NATURE OF THE CIRCULATION AND LIKELY MERGER WITH THE SECONDARY CIRCULATION CENTER. REGARDLESS OF THE EXPECTED DIURNAL PULSES OF CONVECTION, NO SIGNIFICANT CHANGE IN THE INTENSITY IS EXPECTED THROUGH TAU 12. VERY SLOW INTENSIFICATION IS EXPECTED THEREAFTER AS THE SYSTEM CONTINUES TO TAPS INTO A BETTER OUTFLOW ENVIRONMENT BUT REMAINS CONSTRAINED BY A LARGE AMOUNT OF DRY AIR ALL ALONG THE WESTERN PORTIONS OF THE CIRCULATION. AFTER MERGER WITH THE SECONDARY CIRCULATION, THE INTENSITY WILL MAX OUT, THOUGH THE WIND FIELD IS EXPECTED TO BE VERY ASYMMETRIC, LINEAR IN NATURE WITH THE LLCC, AND ASSOCIATED VORTICITY MAXIMUM RUNNING UP THE INSIDE OF THE LINEAR BAND OF ELEVATED WINDS. THE SYSTEM BEGINS TO WEAKEN AFTER TAU 96 AS IT IS FORECAST TO MOVE UNDER A 200MB JET STREAK AND POTENTIALLY SPLIT INTO TWO SEPARATE CIRCULATIONS. MODEL DISCUSSION: TRACK GUIDANCE IS IN MARGINAL CROSS-TRACK AGREEMENT WITH THE GFS AND ECMWF MARKING THE EASTERN OUTLIERS AND THE ECMWF ENSEMBLE MEAN MARKING THE WESTERN BOUNDARY OF THE GUIDANCE PACKAGE (WHICH IS AN INTERESTING DILEMMA IN AND OF ITSELF). THE MAJORITY OF THE GUIDANCE SUPPORTS THE JTWC FORECAST TRACK THROUGH TAU 48, BUT THEREAFTER BEGINS TO OUTRACE THE FORECAST TO A LARGE DEGREE. ALONG-TRACK SPREAD INCREASES TO MORE THAN 600NM BY TAU 120, WITH SOME OF THE MESOSCALE MODELS EXCEEDING MORE THAN 800NM DOWNSTREAM FROM THE CONSENSUS MEAN. ENSEMBLE GUIDANCE SHOWS SIMILAR UNCERTAINTY AFTER TAU 48 AFTER THE CIRCULATION MERGER OCCURS. THE JTWC FORECAST LIES CLOSE TO THE PREVIOUS FORECAST AND THE CONSENSUS MEAN THROUGH THE FORECAST, WITH LOW CONFIDENCE. IN TERMS OF INTENSITY, THE JTWC FORECAST DEVIATES SIGNIFICANTLY LOWER THAN THE CONSENSUS MEMBERS THROUGH THE FORECAST PERIOD. CURIOUSLY, SEVERAL RAPID INTENSIFICATION (RI) AIDS CONTINUE TO FIRE, WHICH IS CONSIDERED EXTREMELY UNLIKELY IN LIGHT OF THE CURRENT SYNOPTIC CONDITIONS. THE CONSENSUS MEAN AND HAFS-A PEAK THE SYSTEM AT 65 KNOTS, WHILE CTCX PEAKS SLIGHTLY LOWER AT 55 KNOTS. THE JTWC FORECAST IS BELOW THAT BASED ON ANALYSIS OF THE ENVIRONMENTAL CONDITIONS THROUGH THE FORECAST PERIOD, THOUGH CONFIDENCE IS VERY LOW DUE TO THE LARGE DEVIATION FROM THE MODEL GUIDANCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: LOW TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: LOW INTENSITY 72-120 HR: LOW NNNN