WDXS31 PGTW 110300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (EIGHTEEN) WARNING NR 010// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 14.0S 121.4E INITIAL INTENSITY: 50 KTS GEOGRAPHIC REFERENCE: 239 NM NORTH OF BROOME, AUSTRALIA MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 07 KTS SIGNIFICANT WAVE HEIGHT: 23 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS DISORGANIZED BLOOMS OF CONVECTION TO THE SOUTHWEST OF AN ASSESSED LOW LEVEL CIRCULATION CENTER (LLCC). A 102159Z SSMIS 91 GHZ PASS SHOWS THE AFOREMENTIONED CONVECTION TO THE SOUTHWEST OF SOME LOW LEVEL BANDING FEATURES WRAPPING INTO THE LLCC. TC EIGHTEEN IS IN A FAVORABLE ENVIRONMENT FOR FURTHER TROPICAL DEVELOPMENT. THESE CONDITIONS ARE CHARACTERIZED BY GOOD POLEWARD OUTFLOW ALOFT, A STRONG 850 MB VORTICITY SIGNATURE, LOW (5-10 KTS) VERTICAL WIND SHEAR (VWS), AND VERY WARM (29-30 C) SEA SURFACE TEMPERATURES (SST). THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON MULTI-AGENCY FIXES, AS WELL AS THE AFOREMENTIONED MSI. THE INITIAL INTENSITY OF 50 KNOTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED OFF A BLEND OF AUTOMATED AND MULTI-AGENCY DVORAKS ESTIMATES. 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: T3.0 - 45 KTS APRF: T3.0 - 45 KTS CIMSS SATCON: 47 KTS AT 101657Z CIMSS ADT: 51 KTS AT 102030Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE POLEWARD ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM 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 18S IS RIDING THE NORTHWESTERN PERIPHERY OF THE SUBTROPICAL RIDGE TO THE EAST. AS IT CONTINUES THIS TRAJECTORY, THE SYSTEM WILL INTENSIFY AS THE VWS IS EXPECTED TO LOWER THROUGHOUT THE FORECAST PERIOD. BY TAU 12, THE INTENSITY WILL INCREASE TO 60 KTS, AND THEN FURTHER INCREASING TO 80 KTS BY TAU 24. BY TAU 36, TC 18S WILL BEGIN TO ROUND THE RIDGE AXIS AND SHIFT TO A MORE SOUTHWARD TRACK WHILE IT JUMPS UP TO 105 KTS. UPON COMPLETION OF ROUNDING THE RIDGE AXIS, THE SYSTEM WILL BEGIN A SOUTHEASTWARD TRAJECTORY AND REACH ITS MAX INTENSITY OF 130 KTS. AS TC 18S MAKES ITS APPROACH TO LAND, IT WILL PASS OVER A POOL OF WARMER (30-31 C) SSTS, CONTRIBUTING TO MAINTAINING ITS INTENSITY AS IT PICKS UP TRACK SPEED. JUST AFTER TAU 60, TC 18S WILL MAKE LANDFALL ALMOST AT THE CENTER POINT OF EIGHTY MILE BEACH, AUSTRALIA. AFTER A PERIOD OF LAND INTERACTION, THE SYSTEM WILL BEGIN ITS DISSIPATION PHASE AND DECREASE TO 75 KTS BY TAU 72, FURTHER DECREASING AND BECOME FULLY DISSIPATED BY TAU 96. MODEL DISCUSSION: THE DETERMINISTIC AND ENSEMBLE MODELS ALL AGREE THAT TC EIGHTEEN WILL CONTINUE TO INTENSIFY AS IT TRANSITS TO THE SOUTHWEST BEFORE ROUNDING THE RIDGE AXIS AND SHIFTING SOUTHWARD AFTER TAU 36, AND FURTHER SHIFTING SOUTHEASTWARD AND CONTINUE TO INTENSIFY AFTER TAU 48. FOR THE JTWC FORECAST TRACK CONSENSUS MEMBERS, THERE IS A 26 NM SPREAD AT TAU 12. THIS TRACK SPREAD GRADUALLY INCREASES TO 102 NM BY TAU 60, JUST BEFORE LANDFALL. GFS AND ECMWF ARE ON THE EASTERN PORTION OF THE CONSENSUS ENVELOPE, WHEREAS NAVGEM AND UK TRACK MODELS ARE ON THE WESTERN PORTION. BECAUSE OF THE GRADUAL INCREASE IN THE TRACK MODEL SPREAD, THE JTWC FORECAST TRACK IS PLACED WITH MEDIUM CONFIDENCE UP TO TAU 72, THEN LOW CONFIDENCE AFTERWARDS. THE INTENSITY CONSENSUS MEMBERS ARE ALSO IN AGREEMENT DISPLAYING A RAPIDLY INTENSIFYING SYSTEM BETWEEN TAUS 24 AND 66, THEN A SUDDEN DROP OFF AFTER TAU 66 WHEN THE SYSTEM MAKES LANDFALL. THE JTWC FORECAST INTENSITY IS SET WITH MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN