WDXS32 PGTW 310300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 09S (GRANT) WARNING NR 028// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 15.0S 73.1E INITIAL INTENSITY: 105 KTS GEOGRAPHIC REFERENCE: 475 NM SOUTH OF DIEGO GARCIA MOVEMENT PAST 6 HOURS: WESTWARD AT 14 KTS SIGNIFICANT WAVE HEIGHT: 28 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL CYCLONE 09S (GRANT) WITH A FILLED EYE, THOUGH THERE IS A SLIGHT WARM SPOT LEFT OVER WHERE THE EYE WOULD BE AT. THE SYSTEM HAS CONTINUED TO BE HIGHLY COMPACT AS IT FENDS OFF THE INCREASING NORTHEASTERLY SHEAR. A 302231Z F18 SSMIS 91 GHZ MICROWAVE IMAGE REVEALED AN EXTREMELY SMALL INNER-CORE OF DEEP CONVECTION THAT MEASURED TO BE ABOUT 35 NM IN DIAMETER. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE SLIGHT WARM SPOT IN ANIMATED EIR IMAGERY AND EXTRAPOLATION FROM THE SSMIS IMAGE. THE INITIAL INTENSITY OF 105 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A BLEND OF THE AGENCY DVORAK AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW. ENVIRONMENTAL ANALYSIS INDICATES THAT 09S IS IN A MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY STRONG OUTFLOW ALOFT, MODERATE (15-20 KTS) NORTHEASTERLY VERTICAL WIND SHEAR, AND WARM (27-28 C) SEA SURFACE TEMPERATURES. INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK CURRENT STEERING MECHANISM: A SUBTROPICAL RIDGE (STR) CENTERED TO THE SOUTH-SOUTHEAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T6.0 - 115 KTS DEMS: T6.0 - 115 KTS FMEE: T5.5 - 102 KTS FIMP: T5.5 - 102 KTS CIMSS SATCON: 98 KTS AT 302330Z CIMSS ADT: 84 KTS AT 310030Z CIMSS AIDT: 86 KTS AT 310030Z CIMSS D-MINT: 118 KTS AT 302231Z CIMSS D-PRINT: 102 KTS AT 310030Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 15-20 KTS SST: 27-28 CELSIUS OUTFLOW: STRONG POLEWARD AND EQUATORWARD 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: TC 09S IS FORECAST TO CONTINUE TRACKING WEST-SOUTHWESTWARD, ALONG THE NORTHWESTERN PERIPHERY OF THE STR CENTERED TO THE SOUTH-SOUTHEAST THROUGH TAU 24. NEAR TAU 24, THE SYSTEM WILL BRIEFLY BE PLACED WITHIN A WEAK STEERING ENVIRONMENT AS THE STR PROPAGATES TO THE EAST, AWAY FROM THE VORTEX. NEAR TAU 48, A SECOND STR WILL BEGIN BUILDING TO THE SOUTH, CAUSING 09S TO MAKE AN EQUATORWARD JOG THROUGH TAU 72. AFTER TAU 72, THE SYSTEM IS FORECAST TO TRACK WEST-SOUTHWESTWARD, ALONG THE NORTHERN PERIPHERY OF THE SECOND STR THROUGH THE REMAINDER OF THE FORECAST PERIOD. REGARDING INTENSITY, 09S IS FORECAST TO STEADILY WEAKEN THROUGH TAU 48 AS NORTHEASTERLY SHEAR REMAINS AROUND 20 KTS. ADDITIONALLY, DRY AIR ENTRAINMENT FROM THE NORTH WILL FURTHER AID IN WEAKENING THE SYSTEM. MESOSCALE MODELS SHOW 09S QUICKLY WEAKENING TO AROUND 40 KTS AT TAU 48, WHICH IS DEFINITELY IN THE REALM OF POSSIBILITIES. HOWEVER, THE JTWC INTENSITY FORECAST KEEPS THE INTENSITY SLIGHTLY HIGHER DUE TO THE COMPACT NATURE OF THE WIND FIELD, WHICH COULD CACOON ITSELF FROM THE DRY AIR. NEAR TAU 84, SHEAR IS EXPECTED TO DROP TO BELOW 10 KTS, ALLOWING FOR 09S TO BEGIN REINTENSIFYING THROUGH THE REMAINDER OF THE FORECAST PERIOD. MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN MODERATE AGREEMENT THROUGHOUT THE FORECAST PERIOD. CROSS-TRACK SPREAD AT AU 72 IS AROUND 230 NM, WITH NAVGEM BEING THE NORTHERNMOST MEMBER AND GALWEM BEING THE SOUTHERNMOST MEMBER. AFTER TAU 72, MODELS FURTHER DIVERGE DUE TO DIFFERING INTERACTIONS WITH THE SECOND STR. CROSS-TRACK SPREAD INCREASES TO OVER 400 NM AND ALONG TRACK SPREAD ALSO CONSIDERABLY INCREASES TO AROUND 320 NM AT TAU 120. THE ECMWF ENSEMBLE MEAN IS THE SLOWEST MODEL WHILE GDM AND GALWEM ARE THE FASTEST. THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS THROUGH TAU 72 AND THEN HEDGED CLOSER TO THE GDM THROUGH TAU 120. INTENSITY GUIDANCE HAS ONE SIGNIFICANT OUTLIER IN COAMPS-TC. ON ONE HAND, HAFS-A AND HWRF BOTH QUICKLY WEAKEN THE SYSTEM TO 40 KTS AT TAU 48 AND MAINTAIN 40 KTS THROUGH TAU 96. ON THE OTHER HAND, COAMPS-TC KEEPS THE SYSTEM ABOVE 65 KTS AND BEGINS REINTENSIFYING AFTERWARD. THE JTWC INTENSITY FORECAST IS PLACED CLOSE TO THE CONSENSUS THROUGH TAU 36 AND THEN ABOUT 10-15 KTS HIGHER THAN HAFS-A AND HWRF AFTERWARD. CONFIDENCE IN THE JTWC INTENSITY FORECAST IS MEDIUM THROUGH TAU 72 AND LOW THEREAFTER. FORECAST CONFIDENCE: TRACK 00-72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN