WDXS31 PGTW 092100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (EIGHTEEN) WARNING NR 005// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 13.3S 124.2E INITIAL INTENSITY: 45 KTS GEOGRAPHIC REFERENCE: 299 NM NORTH-NORTHEAST OF BROOME, AUSTRALIA MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 10 KTS SIGNIFICANT WAVE HEIGHT: 17 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED SATELLITE IMAGERY SHOWS A CONSOLIDATING SYSTEM WITH FRAGMENTED SPIRAL BANDING FEEDING IN FROM ALL QUADRANTS INTO THE COLD DENSE OVERCAST THAT IS OBSCURING THE LOW LEVEL CIRCULATION (LLC). THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON EXTRAPOLATION FROM MICROWAVE LLC FEATURES IN THE 091714Z ATMS AND 091614Z AMSR2 IMAGES. THE INITIAL INTENSITY IS BASED WITH MEDIUM CONFIDENCE FROM AN OVERALL ASSESSMENT OF PGTW AND AUTOMATED DVORAK ESTIMATES AND CONSISTENT WITH THE SUSTAINED EIR CONVECTIVE SIGNATURE OVER THE PAST SIX HOURS. TC 18S IS IN A FAVORABLE ENVIRONMENT WITH LIGHT VWS, STRONG POLEWARD OUTFLOW AND VERY WARM ALONG-TRACK SST. INITIAL WIND RADII BASIS: PERSISTENCE. CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE SOUTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS WIIX: T3.0 - 45 KTS CIMSS SATCON: 39 KTS AT 091715Z CIMSS ADT: 37 KTS AT 091730Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 30-31 CELSIUS OUTFLOW: STRONG 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 WILL CONTINUE TO TRACK SOUTHWESTWARD UNDER THE STEERING STR IN THE SOUTH INDIAN OCEAN. AFTER TAU 48, A TRANSITORY SHORTWAVE TROUGH APPROACHING FROM THE SOUTHWEST WILL ERODE THE STR AND ALLOW THE CYCLONE TO RECURVE SOUTHEASTWARD, MAKE LANDFALL JUST EAST OF PORT HEADLAND AROUND TAU 78, AND TRACK INLAND OVER WESTERN AUSTRALIA. THE FAVORABLE ENVIRONMENT WILL INITIALLY PROMOTE GRADUAL INTENSIFICATION TO 85KTS BY TAU 36. AFTERWARD, LOW VWS, INCREASED OUTFLOW AHEAD OF THE SHORTWAVE TROUGH, AND VERY WARM SST IN THE INDIAN OCEAN WILL FUEL A RAPID INTENSIFICATION (RI) TO A PEAK OF 130KTS BY TAU 72, RIGHT BEFORE LANDFALL. AFTER LANDFALL, INTERACTION WITH THE TERRAIN WILL REDUCE THE INTENSITY TO 40KTS BY TAU 120 AS IT GRADUALLY ERODES OVER LAND. MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL GOOD AGREEMENT WITH THE LAID-OUT FORECAST TRACK, GRADUALLY SPREADING OUT TO A MAXIMUM OF 220NM BY TAU 120. THERE IS HIGH CONFIDENCE IN THE JTWC TRACK FORECAST UP TO TAU 72, THEN LOW AFTERWARD DUE TO THE LAND PASSAGE. THERE IS MEDIUM CONFIDENCE IN THE INTENSITY FORECAST UP TO TAU 72 THEN LOW CONFIDENCE AFTERWARD ON ACCOUNT OF THE HIGH VARIABILITY IN THE INTENSITY GUIDANCE ASSOCIATED WITH RI. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN