WDPN33 PGTW 251500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 25W (NEOGURI) WARNING NR 029// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 32.4N 154.9E INITIAL INTENSITY: 60 KTS GEOGRAPHIC REFERENCE: 776 NM EAST OF YOKOSUKA, JAPAN MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 11 KTS SIGNIFICANT WAVE HEIGHT: 28 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) WITH LOW-LEVEL CLOUDS TIGHTLY WRAPPING INTO THE LLCC AND ASSOCIATED PERSISTENT CONVECTION CONFINED TO THE NORTHWESTERN QUADRANT. THE OVERALL APPEARANCE OF THE STORM HAS DEGRADED OVER THE PAST 6 HOURS, LIKELY DUE TO UPWELLING EFFECTS AND SIGNIFICANT DRY AIR ENTRAINMENT. ENVIRONMENTAL ANALYSIS INDICATES THE ENVIRONMENT IS MARGINALLY FAVORABLE, CHARACTERIZED BY LOW (10-15 KTS) VERTICAL WIND SHEAR, WARM (28-29 C) SEA SURFACE TEMPERATURES, AND STRONG POLEWARD OUTFLOW, OFFSET BY THE UPWELLING AND DRY AIR. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON A 251128Z METOP-B ASCAT IMAGE REVEALING THE LLCC. THE INITIAL INTENSITY OF 60 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK FIXES LISTED BELOW. ADDITIONALLY, A 250731Z RCM- 2 SAR WIND SPEED IMAGE REVEALED A SWATH OF 65-70 KTS IN THE NORTHERN SEMICIRCLE. CIMSS OBJECTIVE ESTIMATES ARE ANALYZED TO BE TOO LOW DUE TO THE WEAK CONVECTIVE STRUCTURE OF THE SYSTEM. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT BETWEEN TWO SUBTROPICAL RIDGES (STR) OF EQUAL STRENGTH POSITIONED TO THE EAST AND WEST OF THE SYSTEM AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T4.0 - 65 KTS RJTD: T3.5 - 55 KTS RCTP: T3.0 - 45 KTS KNES: T3.5 - 55 KTS CIMSS ADT: 35 KTS AT 251140Z CIMSS AIDT: 41 KTS AT 251140Z CIMSS D-PRINT: 43 KTS AT 251210Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 10-15 KTS SST: 28-29 CELSIUS OUTFLOW: STRONG POLEWARD OTHER FACTORS: UPWELLING AND DRY AIR ENTRAINMENT ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TROPICAL STORM (TS) 25W IS FORECAST TO CONTINUE TRACKING SOUTHWESTWARD THROUGH TAU 24, THEN BECOMING QUASI-STATIONARY FROM TAU 24 TO TAU 36. WHILE THE STORM IS QUASI-STATIONARY, ERRATIC MOTION NOT REFLECTED IN THE FORECAST MAY OCCUR. AFTER TAU 36, 25W IS EXPECTED TO LOOP BACK TO THE NORTHEAST AND CONTINUE A NORTHEASTWARD TRACK MOTION UNTIL IT BECOMES FULLY EXTRATROPICAL NEAR TAU 72. BEGINNING AROUND TAU 48, 25W WILL SIGNIFICANTLY ACCELERATE AS IT ENTERS UNDER THE INFLUENCE OF THE UPPER-LEVEL JET AND WILL BEGIN EXTRATROPICAL TRANSITION (ETT) AT THAT TIME. REGARDING INTENSITY, 25W IS FORECAST TO SLIGHTLY WEAKEN BETWEEN TAUS 12-24 TO 55 KTS. INTENSITY IS FORECAST TO INCREASE TO 60-70 KTS AS 25W MOVES NORTHEASTWARD DURING ETT AND POLEWARD OUTFLOW BECOMES MORE ROBUST IN RESPONSE TO INTERACTION WITH THE JET. MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN STRONG AGREEMENT THROUGH TAU 48, WITH ALL MODELS CONTINUING TO SHOW 25W LOOPING OVER ITS PREVIOUS TRACK. AFTER TAU 48, THE GUIDANCE BEGINS TO DEVIATE. AT TAU 72, THE ALONG-TRACK SPREAD IS APPROXIMATELY 320 NM AS JGSM AND GFS FORECAST FASTER TRACK SPEEDS THAN ECMWF AND UKMET, WHICH LAG BEHIND. THE ALONG-TRACK SPREAD INJECTS SOME UNCERTAINTY; HOWEVER, THE JTWC TRACK FORECAST IS STILL PLACED WITH OVERALL MEDIUM CONFIDENCE. RELIABLE INTENSITY IS IN GOOD AGREEMENT IN SLIGHT WEAKENING BETWEEN TAUS 12-24, BEFORE RE-INTENSIFYING WHILE UNDERGOING ETT BETWEEN TAUS 48-72; HOWEVER, THERE IS SOME DISAGREEMENT ON THE PEAK INTENSITY BEFORE 25W BECOMES FULLY EXTRATROPICAL. AS A RESULT, THE JTWC INTENSITY FORECAST IS PLACED WITH OVERALL MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 00-72 HR: MEDIUM INTENSITY 00-72 HR: MEDIUM// NNNN