WDPN31 PGTW 121500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 29W (PAKHAR) WARNING NR 008// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 19.9N 130.6E INITIAL INTENSITY: 35 KTS GEOGRAPHIC REFERENCE: 425 NM SOUTH-SOUTHEAST OF KADENA AB MOVEMENT PAST 6 HOURS: EASTWARD AT 06 KTS SIGNIFICANT WAVE HEIGHT: 15 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL STORM 29W (PAKHAR) HAS RAPIDLY WEAKENED OVER THE PAST SIX HOURS AFTER FIRST BEING DECAPITATED BY A BURST OF STRONG VERTICAL WIND SHEAR (VWS) AND THEN FINISHED OFF BY MID-LEVEL DRY AIR INTRUSION. ANIMATED SHORTWAVE INFRARED (SWIR) SATELLITE IMAGERY SHOWS THAT THE LOW LEVEL CIRCULATION CENTER (LLCC) HAS HUNG BACK AS THE DISORGANIZED CONVECTION HAS RACED OFF TO THE NORTHEAST, WITH THE LOW- LEVEL ROTATION AT TIMES EVIDENT UNDER THIN CIRRUS CLOUDS. THE LLCC IS NOW MERGING WITH A STATIONARY FRONT DRAPED ACROSS THE REGION. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE EVEN THOUGH THE POSITION IS SIGNIFICANTLY SOUTHWEST OF ALL BUT THE PGTW FIX POSITION, BASED ON THE SHALLOW CIRCULATION SEEN IN THE SWIR. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE AT A GENEROUS 35 KNOTS. UNFORTUNATELY, THE RECENT ASCAT PASS MISSED THE CIRCULATION, BUT EARLIER SCATTEROMETER DATA AND A 120918Z PARTIAL SMOS PASS SHOWED A SMALL AREA OF GALE FORCE WINDS TO THE NORTHWEST OF THE CENTER, WHICH PROVIDED ADDITIONAL CONFIDENCE IN THE ADT FINAL-T NUMBER OF 2.3, AND THE DEEP MICRONET AND OPEN-AIIR ESTIMATES NEAR 35 KNOTS. WHILE SHEAR HAS DROPPED OFF AND IS NOW DOWN TO LESS THAN 15 KNOTS, THE SYSTEM IS CLEARLY IN AN UNFAVORABLE ENVIRONMENT WITH THE DRY AIR BEING THE PRIMARY INHIBITING FACTOR AT THIS POINT. INITIAL WIND RADII BASIS: PERSISTENCE AND SMOS DATA CURRENT STEERING MECHANISM: LOW-LEVEL NORTH-NORTHEASTERLY FLOW BEHIND THE STATIONARY FRONT AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T1.0 - 25 KTS RJTD: T2.5 - 35 KTS CIMSS ADT: 47 KTS AT 121140Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE VWS: 15-20 KTS SST: 28-29 CELSIUS OUTFLOW: WEAK POLEWARD OTHER FACTORS: SIGNIFICANT MID-LEVEL DRY AIR INTRUSION ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. THE FORECAST LENGTH HAS BEEN SHORTENED TO 24 HOURS. FORECAST DISCUSSION: VERY DRY MID-LEVEL AIR HAS NOW SMOTHERED TS 29W AND FINISHED OFF THE JOB STARTED BY THE STRONG SHEAR AND THE SYSTEM HAS RAPIDLY WEAKENED TO THE POINT WHERE THE REMAINING VORTEX DOES NOT EXTEND ABOVE THE 850MB LEVEL. AS SUCH THE STEERING MECHANISM HAS NOW SHIFTED TO THE LOW-LEVEL FLOW, WHICH IS COMING OUT OF NORTH-NORTHEAST. THE LLCC HAS ALREADY SLOWED TO A CRAWL AND BEGUN TO TURN TOWARDS THE SOUTHEAST AND THIS TREND IS EXPECTED TO CONTINUE THROUGH THE FORECAST PERIOD WITH THE SYSTEM ENDING UP ON A SOUTHWESTWARD HEADING BY TAU 24. THE SYSTEM WILL CONTINUE TO RAPIDLY WEAKEN THROUGH THE FORECAST PERIOD AS IT HAS NOW LOST ALL UPPER-LEVEL SUPPORT AND WILL CONTINUE TO BE CLOBBERED BY THE DRY AIR AND IS EXPECTED TO FULLY DISSIPATE NO LATER THAN TAU 24. AS THE VORTEX SLIDES SOUTHWARD ALONG THE FRONTAL BOUNDARY AND DISSIPATES, THE WIND FIELD WILL BECOME INCREASINGLY ASYMMETRIC AND THERE WILL BE SOME HIGHER GRADIENT WINDS PRESENT ON THE WEST-NORTHWEST SIDE OF THE CIRCULATION THROUGH AND AFTER THE FORECAST PERIOD. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GOOD AGREEMENT THAT THE SYSTEM WILL CONTINUE TO GRADUALLY TURN TOWARDS THE SOUTH AND THEN SOUTHWEST THROUGH THE SHORT DURATION OF THE FORECAST PERIOD. NAVGEM AND THE UKMET ENSEMBLE REMAIN THE SOLE OUTLIERS, TURNING THE SYSTEM MORE SLOWLY AND KEEPING IT FURTHER TO THE EAST. THE REMAINDER OF THE CONSENSUS MEMBERS ARE TIGHTLY PACKED NEAR THE JTWC TRACK, PROVIDING HIGH CONFIDENCE TO THE FORECAST. INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT, THOUGH THE JTWC FORECAST CALLS FOR A FASTER RATE OF WEAKENING THAN THE CONSENSUS MEAN BASED ON THE RECENT RAPID WEAKENING TRENDS AND TAKING INTO ACCOUNT THAT THE MODELS ARE SENSING THE HIGHER GRADIENT WINDS AND HOLDING ONTO A HIGHER INTENSITY FOR UP TO 48 HOURS. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH INTENSITY 0 - 72 HR: MEDIUM// NNNN