WDXS31 PGTW 111500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (ILSA) WARNING NR 012// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 15.3S 120.9E INITIAL INTENSITY: 65 KTS GEOGRAPHIC REFERENCE: 173 NM NORTH-NORTHWEST OF BROOME, AUSTRALIA MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 06 KTS SIGNIFICANT WAVE HEIGHT: 24 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A LARGE CENTRAL DENSE OVERCAST (CDO) FULLY OBSCURING THE LOW LEVEL CIRCULATION CENTER (LLCC) BENEATH. A 111035Z SSMIS 91GHZ MICROWAVE IMAGE REVEALS THE PREVIOUSLY OFFSET LLCC AND UPPER LEVEL CIRCULATION CENTER (ULCC) HAVE BECOME MUCH CLOSER TO VERTICALLY STACKED. A DEEP CONVECTIVE BAND IS EVIDENT TO THE SOUTH OF THE LLCC WHILE THE COPIOUS AMOUNTS OF DRY AIR TO THE WEST ATTEMPT TO ENTRAIN THE SYSTEM FROM THE NORTH. A RECENT 111024Z SCATTEROMETRY PASS FURTHER INDICATES A SMALL TIGHT CIRCULATION NEAR THE CENTER OF THE CDO. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON EIR, SSMIS AND SCATTEROMETERY DATA. THE INITIAL INTENSITY OF 65 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON AGENCY DVORAK INTENSITY ESTIMATES STRUGGLING TO RECONCILE THE CHANGE IN SCENE TYPE COUPLED WITH THE LOSS OF VISIBLE IMAGERY RESULTING IN A RANGE OF T3.0-T4.0 WHILE AUTOMATED ESTIMATES HOVER NEAR 60KTS. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE EAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS KNES: T3.5 - 55 KTS APRF: T4.0 - 65 KTS CIMSS ADT: 61 KTS AT 111313Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 10-15 KTS SST: 30-31 CELSIUS OUTFLOW: MODERATE POLEWARD OTHER FACTORS: POSSIBLE ONSET OF RAPID INTENSIFICATION (RI). ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM 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: TC 18S (ILSA) IS FORECAST TO CONTINUE TRACKING SOUTHWESTWARD UNDER THE STEERING INFLUENCE OF THE STR TO THE EAST. THROUGH TAU 36, THE ENVIRONMENT AROUND 18S WILL CONTINUE TO SHIFT FROM FAVORABLE TO HIGHLY FAVORABLE, CHARACTERIZED BY WARM SSTS (30-31C), LOW VERTICAL WIND SHEAR AND IMPROVING OUTFLOW ALOFT. AS THE SYSTEM APPROACHES THE STR AXIS NEAR TAU 36, THE SYSTEM IS FORECAST TO BE NEAR 115KTS. AS 18S BEGINS TO TURN POLEWARD AND EVENTUALLY SOUTH-SOUTHEASTWARD, SST AND OHC VALUES COMBINED WITH ROBUST OUTFLOW ALOFT WILL FUEL ILSA TO A PEAK INTENSITY NEAR 120KTS AND POSSIBLY HIGHER BEFORE WEAKENING AS THE SYSTEM APPROACHES LAND. AFTER TAU 48, ILSA WILL MAKE LANDFALL NEAR THE CENTER POINT OF EIGHTY MILE BEACH AND PROCEED INLAND, QUICKLY WEAKENING THROUGH TAU 72 AND EVENTUALLY DISSIPATING NEAR TAU 96. MODEL DISCUSSION: NUMERICAL MODELS ARE IN GOOD AGREEMENT THAT 18S WILL ROUND THE STR AXIS AND MAKE LANDFALL BETWEEN BROOME AND PORT HEDLAND WITH AN 85NM SPREAD IN SOLUTIONS BY LANDFALL. AS A RESULT THE JTWC TRACK FORECAST IS PLACED WITH MEDIUM CONFIDENCE. RELIABLE MODEL INTENSITY GUIDANCE IS IN FAIR AGREEMENT WITH ALL MEMBERS INDICATING AN INTENSIFICATION TREND THROUGH TAU 36 AND AFTER TAU 48 INTENSITIES SHARPLY DECLINE THROUGH THE FORECAST PERIOD. DURING THE INITIAL INTENSIFICATION, SEVERAL RAPID INTENSIFICATION (RI) AIDS ARE TRIGGERING, DECAY-SHIPS INDICATES A PEAK INTENSITY NEAR 95KTS BY TAU 36 WHILE COAMPS-TC (NAVGEM VERSION) AND GFS PEAK NEAR 115KTS THOUGH THE TRUE PEAK LIES NEAR TAU 42. FOR THESE REASONS THE JTWC INTENSITY FORECAST IS PLACED WITH MEDIUM CONFIDENCE AND EVENTUALLY HIGH CONFIDENCE AFTER LANDFALL. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: HIGH// NNNN