WDXS32 PGTW 021500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 09S (GRANT) WARNING NR 033// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 15.2S 66.6E INITIAL INTENSITY: 35 KTS GEOGRAPHIC REFERENCE: 597 NM SOUTHWEST OF DIEGO GARCIA MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 05 KTS SIGNIFICANT WAVE HEIGHT: 14 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A COMPACT AND WELL-DEFINED LOW LEVEL CIRCULATION CENTER (LLCC) WITH DISORGANIZED, PULSING DEEP CONVECTION DEVELOPING ALONG THE CONVERGENCE LINES ON THE WESTERN FLANK OF THE LLCC. A 021038Z GMI 37GHZ MICROWAVE IMAGE REVEALED A WELL-DEFINED LLCC AS OUTLINED BY A COMPACT LOW EMISSIVITY REGION SURROUNDED BY SHALLOW CONVECTIVE BANDING FEATURES. ANIMATED WATER VAPOR IMAGERY AND CIRA DERIVED MOTION WINDS (DMW) DEPICT VERY WEAK OUTFLOW ALOFT, WITH LIGHT (10-15 KNOTS) WINDS PUSHING POLEWARD FROM THE CENTER. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON AN EXTRAPOLATION OF THE LLCC IN THE MICROWAVE IMAGE NOTED ABOVE AND THE PARTIALLY EXPOSED LLCC IN THE ANIMATED MSI. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, WEIGHTED TOWARDS THE PGTW DVORAK CURRENT INTENSITY ESTIMATE AND THE BULK OF THE OBJECTIVE ESTIMATES OUTLINED BELOW. ENVIRONMENTAL CONDITIONS ARE MARGINALLY UNFAVORABLE, CHARACTERIZED BY MODERATE NORTHEASTERLY SHEAR, WEAK OUTFLOW ALOFT, DRY MID-LEVEL AIR AND WARM SSTS. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A SMALL SUBTROPICAL RIDGE (STR) POSITIONED TO THE SOUTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS FMEE: T2.0 - 30 KTS CIMSS SATCON: 36 KTS AT 021200Z CIMSS ADT: 34 KTS AT 021200Z CIMSS AIDT: 33 KTS AT 021200Z CIMSS D-MINT: 34 KTS AT 021041Z CIMSS D-PRINT: 29 KTS AT 021200Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY UNFAVORABLE VWS: 15-20 KTS SST: 27-28 CELSIUS OUTFLOW: WEAK POLEWARD OTHER FACTORS: VERY DRY MID-LEVEL AIR ENTRENCHED ACROSS THE EASTERN HALF OF THE SYSTEM. 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. FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 09S (GRANT) HAS MAINTAINED A NORTHWESTWARD TRACK OVER THE PAST 24 HOURS, STEERED ALONG THE NORTHERN SIDE OF A SMALL STR TO THE SOUTHWEST, WHICH ITSELF IS MOVING NORTHWESTWARD, IN EFFECT PUSHING TC 09S OUT IN FRONT OF IT. OVER THE NEXT 12 HOURS, TC 09S WILL BEGIN TO TURN WESTWARD, THEN BY TAU 24, TAKE A TURN TOWARDS THE WEST-SOUTHWEST, AS THE RIDGE STRENGTHENS AND MOVES TOWARDS THE SOUTHWEST, ROUGHLY IN PHASE WITH TC 09S. AFTER TAU 72, TC 09S WILL ASSUME A MORE SOUTHWESTWARD TRAJECTORY AS THE STR RECEDES BACK TOWARDS THE EAST. WHILE THE TRACK IS RELATIVELY STRAIGHT-FORWARD, THE INTENSITY FORECAST PRESENTS A SIGNIFICANT CHALLENGE. CURRENT CONDITIONS ARE MARGINAL, BUT THE MAJORITY OF THE GLOBAL AND MESOSCALE MODELS SUGGEST SHEAR SHOULD LESSEN OVER THE NEXT 12 TO 24 HOURS. ADDITIONALLY, THE ENVIRONMENT IS EXPECTED TO MOISTEN, ESPECIALLY AFTER TAU 36 AND AROUND TAU 48, THE SYSTEM IS FORECAST TO EXPERIENCE SLIGHTLY IMPROVED EQUATORWARD OUTFLOW CONDITIONS. THE COMBINATION OF THESE FACTORS SUPPORT MAINTAINING THE CURRENT INTENSITY FOR THE NEXT 36 HOURS, FOLLOWED BY A PERIOD OF SLIGHT INTENSIFICATION THROUGH APPROXIMATELY TAU 72. SHEAR IS EXPECTED TO INCREASE AGAIN AFTER TAU 72, WHICH WILL INDUCE A SLOW WEAKENING TREND. THE SYSTEM IS FORECAST TO MAKE LANDFALL ALONG THE EASTERN COAST OF MADAGASCAR PRIOR TO TAU 120, AT WHICH POINT IT WILL ALREADY BE WEAKENING, THUS IT WILL DISSIPATE RAPIDLY ONCE IT MOVES ASHORE. MODEL DISCUSSION: THE MAJORITY OF THE AVAILABLE DETERMINISTIC, ENSEMBLE AND ARTIFICIAL INTELLIGENCE (AI) MODELS, WITH THE EXCEPTION OF NAVGEM, ARE IN GOOD OVERALL AGREEMENT ON THE TRACK SCENARIO. THE NAVGEM SOLUTION, WHICH EXHIBITS A KNOWN POLEWARD BIAS, IS AN OUTLIER THAT IS SKEWING THE CONSENSUS MEAN POLEWARD. DISCOUNTING THE NAVGEM AND THE CONSENSUS MEAN, THE REMAINDER OF THE GUIDANCE PACKAGE IS CONTAINED WITHIN AN ENVELOPE THAT GRADUALLY EXPANDS TO 90NM AT TAU 72, AND 170NM AT TAU 120. THE ECMWF AND GDM MEAN ARE POSITIONED ON THE NORTHERN EDGE AND THE EC-AIFS ON THE SOUTHERN SIDE. THE ECMWF IS SIGNIFICANTLY SLOWER THAN THE OTHER MODELS, WHICH INDUCES AN ALONG-TRACK SPREAD OF APPROXIMATELY 200NM AT TAU 96, HOWEVER THE REMAINDER OF THE MODELS ARE FAIRLY WELL CONSTRAINED IN ALONG-TRACK DIRECTION. THE JTWC FORECAST IS POSITIONED NEAR THE AI-MODEL CONSENSUS MEAN AND ECMWF ENSEMBLE MEAN WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS GENERALLY CONSISTENT, WITH ALL MODELS SHOWING A RELATIVELY STABLE INTENSITY TREND BETWEEN 30 AND 40 KNOTS, AND A SLIGHT INCREASE AFTER TAU 48 BEFORE WEAKENING AGAIN AFTER TAU 96. THE TWO OUTLIERS ARE THE HWRF AND COTC, WHICH SHOW MUCH MORE SIGNIFICANT INTENSIFICATION AFTER TAU 48, UP TO A PEAK AS HIGH AS 60 KNOTS AROUND TAU 96. HOWEVER, THESE MODELS ALSO HAVE A MUCH FLATTER TRACK, HEADED TOWARDS THE NORTHERN TIP OF MADAGASCAR AND SO ARE NOT CONSISTENT WITH THE TRACK FORECAST OR THE OTHER TRACK GUIDANCE AND ARE AND ARE CONSIDERED LOW- PROBABILITY SCENARIOS. FORECAST CONFIDENCE: TRACK 00-72 HR: MEDIUM TRACK 72-120 HR: MEDIUM INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN