WDXS32 PGTW 161500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (EIGHTEEN) WARNING NR 022// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 17.0S 113.9E INITIAL INTENSITY: 35 KTS GEOGRAPHIC REFERENCE: 318 NM NORTH OF LEARMONTH, AUSTRALIA MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 03 KTS SIGNIFICANT WAVE HEIGHT: 15 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS TROPICAL CYCLONE (TC) 18S (EIGHTEEN) WITH IMPROVED DEEP CONVECTIVE BURSTS OVER A BROAD LOW-LEVEL CIRCULATION CENTER (LLCC). A 161038Z SSMIS 91 GHZ SATELLITE MICROWAVE IMAGE REVEALS THE DEEP CONVECTION STRADDLING EITHER SIDE OF THE LLCC IN THE WESTERN AND EASTERN QUADRANTS OF THE SYSTEM. ENVIRONMENTAL ANALYSIS INDICATES THAT TC 18S IS IN A MARGINAL ENVIRONMENT FOR INTENSIFICATION WITH MODERATE WESTWARD OUTFLOW ALOFT, LOW TO MODERATE (15-20 KTS) EASTERLY VERTICAL WIND SHEAR, AND WARM (29-30 C) SEA SURFACE TEMPERATURES. THE INITIAL POSITION IS PLACED WITH LOW CONFIDENCE BASED ON THE AFOREMENTIONED SSMIS SATELLITE MICROWAVE IMAGE DEPICTING A BROAD LLCC, AND DUE TO THE FACT THAT THE LLCC IS OBSCURED BY THE CONVECTIVE BURSTS. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE OBJECTIVE AND SUBJECTIVE INTENSITY ESTIMATES LISTED BELOW. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.0 - 30 KTS KNES: T2.0 - 30 KTS DEMS: T2.0 - 30 KTS APRF: T2.0 - 30 KTS CIMSS AIDT: 39 KTS AT 161300Z CIMSS DPRINT: 32 KTS AT 161200Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL VWS: 15-20 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE WESTWARD ANALYSIS CONFIDENCE: INITIAL POSITION: LOW 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 IS CURRENTLY SLOWLY TRACKING NORTH- NORTHWESTWARD WHILE LOCATED WITHIN A COMPETING STEERING ENVIRONMENT. A NEAR EQUATORIAL RIDGE TO THE NORTH AND A SUBTROPICAL RIDGE TO THE SOUTH ARE CAUSING THE SYSTEM TO DRIFT SLOWLY IN A QUASI-STATIONARY FASHION. TC 18S IS FORECAST TO MAINTAIN A WEAK STEERING MECHANISM OVER THE NEXT 48 HOURS. DURING THIS TIME THERE IS A VARIETY OF DIFFERENT TRACKS THE SYSTEM COULD TAKE, AND THE MODEL GUIDANCE SUGGESTS THAT. TC 18S IS FORECAST TO TRACK SLOWLY NORTHWESTWARD UNTIL TAU 12. AFTER TAU 12, TC 18S IS FORECAST TO START A SOUTHWESTWARD TURN AND MEANDER SOUTHWARD FROM TAU 24-48. AFTER TAU 48, THE STEERING MECHANISM WILL BE MORE DEFINED, AND THE SYSTEM IS EXPECTED TO TRACK WESTWARD ALONG THE NORTHERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) FOR THE REMAINDER OF THE FORECAST PERIOD WITH TRACK SPEEDS INCREASING. REGARDING INTENSITY, THE JTWC INTENSITY FORECASTS HAS TC 18S SLOWLY INTENSIFYING TO 55 KTS BY TAU 120. TC 18S IS ANTICIPATED TO REMAIN IN A MARGINAL ENVIRONMENT, BUT AS THE STEERING PATTERN IMPROVES AND TRACK SPEEDS INCREASE, THE SYSTEM IS EXPECTED TO GRADUALLY INTENSIFY. MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE REMAINS IN RELATIVELY POOR AGREEMENT, ESPECIALLY THROUGH TAU 72, AS IS SOMEWHAT EXPECTED DUE TO THE COMPETING STEERING MECHANISM. AS SUCH, THE TRACK FORECAST CONFIDENCE IS ASSESSED WITH OVERALL LOW CONFIDENCE. GFS HAS BACKED OFF ON TRACKING THE SYSTEM FAR SOUTH AND THEN NORTH, AND COINCIDES WITH THE REST OF THE GUIDANCE BETTER THIS CYCLE. NAVGEM REMAINS THE OUTLIER BY TRACKING THE SYSTEM STRAIGHT SOUTHWARD THROUGH TAU 48 BEFORE MAKING THE WESTWARD TURN. THE JTWC INTENSITY FORECAST CLOSELY ALIGNS TO THE JTWC INTENSITY CONSENSUS. A VERY LARGE INTENSITY SPREAD OF 80KTS IS PRESENT AMONG INTENSITY CONSENSUS MEMBERS BY TAU 120, LENDING LOW CONFIDENCE TO THE OVERALL INTENSITY FORECAST. FORECAST CONFIDENCE: TRACK 0 - 72 HR: LOW TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: LOW INTENSITY 72-120 HR: LOW// NNNN