WDXS31 PGTW 102100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (EIGHTEEN) WARNING NR 009// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 13.7S 122.1E INITIAL INTENSITY: 50 KTS GEOGRAPHIC REFERENCE: 252 NM NORTH OF BROOME, AUSTRALIA MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 07 KTS SIGNIFICANT WAVE HEIGHT: 21 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TC 18S (EIGHTEEN) CONTINUES ITS SLOW CRAWL TOWARDS THE SOUTHWEST, WHILE STRUGGLING TO INTENSIFY IN THE FACE OF PERSISTENT NORTHEASTERLY VERTICAL WIND SHEAR (VWS). ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY INDICATES THAT TC 18S HAS DEVELOPED A CENTRAL DENSE OVERCAST (CDO), WITH DEEP CONVECTION SYMMETRIZING NEAR THE ASSESSED LOW LEVEL CIRCULATION CENTER (LLCC). OVERSHOOTING TOPS WITH TEMPERATURES APPROACHING -91C AND ACCOMPANYING LIGHTNING BURSTS, ARE FIRING IN THE VICINITY OF THE LLCC, POTENTIALLY INDICATING THE LONG-AWAITING ONSET OF A STEADY INTENSIFICATION TREND. OUTER LOW-LEVEL BANDS ARE EVIDENT TO THE EAST OF THE CIRRUS SHIELD AND PROVIDED ASSISTANCE IN PLACING THE INITIAL POSITION. LATE-RECEIPT OF A 101726Z AMSR2 COLOR ENHANCED 89GHZ IMAGE SUGGESTS THE LLCC COULD BE SLIGHTLY FURTHER SOUTHWEST THAN ORIGINALLY THOUGHT. THE AMSR2 IMAGERY ALSO SHOWS AN EXTENSIVE AREA OF INTENSE CONVECTION EXTENDING SOUTHWARD THAT REMAINS RELATIVELY DISORGANIZED. THE INITIAL INTENSITY IS HEDGED UPWARDS TO 50 KNOTS WITH MEDIUM CONFIDENCE, HEDGED TOWARDS THE ADT AND KNES ESTIMATES IN LIGHT OF THE IMPROVING SATELLITE SIGNATURE. ANALYSIS REVEALS THAT ENVIRONMENTAL CONDITIONS ARE STARTING TO IMPROVE. CIMSS SHEAR ANALYSIS IS NOW ESTIMATED AT 14 KNOTS, WHILE HIGH-RESOLUTION MODEL DATA SHOWS A SIMILAR DEEP-LAYER SHEAR AVERAGE. HOWEVER, THE 12Z SOUNDING FROM BROOME STILL SHOWS AROUND 20-25 KNOTS, WHICH MATCHES THE 12Z CIMSS ESTIMATE. BOTTOM LINE, THE PRIMARY LIMITING FACTOR (VWS) ON INTENSIFICATION IS BEGINNING TO WEAKEN ITS STRANGLE HOLD ON THE SYSTEM. INITIAL WIND RADII BASIS: PERSISTENCE AND SCATTEROMETER DATA CURRENT STEERING MECHANISM: NORTHWEST PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) TO THE SOUTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS KNES: T3.5 - 55 KTS APRF: T2.5 - 35 KTS CIMSS SATCON: 46 KTS AT 101657Z CIMSS ADT: 51 KTS AT 101800Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 10-15 KTS SST: 30-31 CELSIUS OUTFLOW: MODERATE POLEWARD 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 CONTINUES TO TRACK TOWARDS THE SOUTHWEST AT A RATHER LEISURELY 6-7 KNOTS. RECENT ANIMATED EIR SUGGESTS THAT THE LLCC, WHICH WAS PREVIOUSLY EXPOSED, MAY HAVE SLOWED DOWN A BIT AND TUCKING UNDER THE DEEP, INCREASINGLY SYMMETRICAL CONVECTIVE MASS. REGARDLESS, THE OVERALL STEERING INFLUENCE HAS NOT CHANGED AND THE SYSTEM IS FORECAST TO TRACK SOUTHWESTWARD ALONG THE WEST SIDE OF THE STR, FOR THE NEXT 36 HOURS. BY TAU 48 THE SYSTEM IS EXPECTED TO REACH AN INFLECTION POINT, IN THE VICINITY OF ROWLEY SHOALS, AND BEGIN TO ROUND THE RIDGE AXIS. BY TAU 60 THE SYSTEM WILL BE FIRMLY ON A SOUTHEASTWARD TRACK, WITH LANDFALL EXPECTED ALONG EIGHTY MILE BEACH BETWEEN TAU 60 AND TAU 72, FOLLOWED BY AN ACCELERATING TRACK INTO CENTRAL AUSTRALIA THROUGH TAU 96. AS DISCUSSED ABOVE, THE SYSTEM CONTINUES TO STRUGGLE AGAINST THE PERSISTENT EASTERLY SHEAR, BUT SIGNS ARE POINTING TO THE SHEAR FINALLY BEGINNING TO RELAX. COMBINED WITH THE RECENT DIURNAL CONVECTIVE MAXIMUM, IT IS LIKELY THAT THE SYSTEM IS NOW IN THE INITIAL PHASE OF INTENSIFICATION. INTENSIFICATION IS EXPECTED TO REMAIN FAIRLY SLOW FOR THE NEXT 24 HOURS AS THE SYSTEM CONTINUES TO CONSOLIDATE AND SYMMETRIZE THE CONVECTIVE CORE. RAPID INTENSIFICATION IS EXPECTED TO BEGIN IN EARNEST AFTER TAU 24, AS THE SYSTEM DEVELOPS A MESOSCALE POINT SOURCE ALOFT AND THE SYSTEM TAPS INTO THE STRONG POLEWARD OUTFLOW AHEAD OF THE APPROACHING UPPER-LEVEL TROUGH WEST OF AUSTRALIA. PEAK INTENSITY OF AT LEAST 130 KNOTS IS STILL ANTICIPATED JUST PRIOR TO LANDFALL AS THE SYSTEM MOVES OVER THE SHALLOW, EXTREMELY WARM (31-32C) WATERS, WITH EXTREME OHC VALUES APPROACHING 170 KJ PER CM2. ONCE ASHORE, THE SYSTEM WILL LIKELY BE SLOW TO WEAKEN INITIALLY, THOUGH IT IS EXPECTED TO RAPIDLY WEAKEN TO A WEAK SUBTROPICAL DEPRESSION OVER CENTRAL AUSTRALIA BY TAU 96. MODEL DISCUSSION: TRACK GUIDANCE IS IN OVERALL GOOD AGREEMENT ON THE GENERAL TRACK, THOUGH WITH SOME MARGINAL SPREAD IN THE DETERMINISTIC GUIDANCE DUE TO DISAGREEMENT ON THE LOCATION AND TIMING OF WHEN THE SYSTEM ROUNDS THE RIDGE AXIS. CROSS-TRACK SPREAD REACHES A MAXIMUM OF 120NM AT TAU 48, THEN TIGHTENS UP TO JUST 75NM AT LANDFALL. ALONG-TRACK SPREAD HAS INCREASED WITH THIS MODEL RUN, WITH SIGNIFICANT SPEED DIFFERENCES BETWEEN THE ECMWF AND GFS BEING OF PARTICULAR NOTE. THE ECMWF IS MUCH SLOWER WITH THIS RUN, WHILE THE GFS CONTINUES TO ACCELERATE THE SYSTEM MUCH FASTER AFTER ROUNDING THE RIDGE. THE JTWC TRACK REMAINS CONSISTENT WITH THE PREVIOUS FORECAST, THOUGH THE TRACK IS SLOWER AFTER TAU 48, RESULTING IN A LATER LANDFALL. INTENSITY GUIDANCE IS IN GOOD AGREEMENT IN SHOWING STEADY TO RAPID INTENSIFICATION THROUGH TAU 60. HWRF AND GFS ARE THE MOST AGGRESSIVE MODELS, INDICATING A PEAK OF 130-135 KNOTS PRIOR TO LANDFALL, WHILE THE COAMPS-TC ALSO SHOWS A PEAK IN THE SAME RANGE, THOUGH ABOUT 12 HOURS LATER. MULTIPLE RAPID INTENSIFICATION (RI) AIDS INCLUDING DTOPS, RICN AND FRIA ARE ALL TRIGGERING, AND THE COAMPS-TC ENSEMBLE (CTCXEPS) CONTINUES TO INDICATE A 95 PERCENT PROBABILITY OF RI BETWEEN TAU 24 TO TAU 60, LENDING HIGH CONFIDENCE TO THE RI SCENARIO. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN