WTXS31 PGTW 041500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/TROPICAL CYCLONE 18S (EIGHTEEN) WARNING NR 017// RMKS/ 1. TROPICAL CYCLONE 18S (EIGHTEEN) WARNING NR 017 01 ACTIVE TROPICAL CYCLONE IN SOUTHIO MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE WIND RADII VALID OVER OPEN WATER ONLY --- WARNING POSITION: 041200Z --- NEAR 24.6S 113.4E MOVEMENT PAST SIX HOURS - 235 DEGREES AT 03 KTS POSITION ACCURATE TO WITHIN 040 NM POSITION BASED ON CENTER LOCATED BY A COMBINATION OF SATELLITE, RADAR AND SYNOPTIC DATA PRESENT WIND DISTRIBUTION: MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT WIND RADII VALID OVER OPEN WATER ONLY RADIUS OF 034 KT WINDS - 030 NM NORTHEAST QUADRANT 030 NM SOUTHEAST QUADRANT 060 NM SOUTHWEST QUADRANT 045 NM NORTHWEST QUADRANT REPEAT POSIT: 24.6S 113.4E --- FORECASTS: 12 HRS, VALID AT: 050000Z --- 24.9S 113.0E MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT WIND RADII VALID OVER OPEN WATER ONLY RADIUS OF 034 KT WINDS - 010 NM NORTHEAST QUADRANT 050 NM SOUTHEAST QUADRANT 080 NM SOUTHWEST QUADRANT 010 NM NORTHWEST QUADRANT VECTOR TO 24 HR POSIT: 195 DEG/ 04 KTS --- 24 HRS, VALID AT: 051200Z --- 25.6S 112.8E MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT WIND RADII VALID OVER OPEN WATER ONLY DISSIPATING AS A SIGNIFICANT TROPICAL CYCLONE OVER WATER RADIUS OF 034 KT WINDS - 000 NM NORTHEAST QUADRANT 090 NM SOUTHEAST QUADRANT 080 NM SOUTHWEST QUADRANT 030 NM NORTHWEST QUADRANT VECTOR TO 36 HR POSIT: 165 DEG/ 06 KTS --- 36 HRS, VALID AT: 060000Z --- 26.8S 113.1E MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT WIND RADII VALID OVER OPEN WATER ONLY DISSIPATED AS A SIGNIFICANT TROPICAL CYCLONE OVER WATER --- REMARKS: 041500Z POSITION NEAR 24.7S 113.3E. 04FEB21. TROPICAL CYCLONE (TC) 18S (EIGHTEEN), LOCATED APPROXIMATELY 143 NM SOUTH-SOUTHWEST OF LEARMONTH, AUSTRALIA, HAS TRACKED SOUTHWESTWARD AT 03 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS FLARING DEEP CONVECTION EAST OF A DEFINED LOW-LEVEL CIRCULATION CENTER, WHICH SUPPORTS THE INITIAL POSITION WITH GOOD CONFIDENCE. THE CENTER IS LOCATED APPROXIMATELY 22NM NORTHWEST OF CARNARVON, WHICH IS REPORTING SUSTAINED SURFACE WINDS (10-MINUTE AVERAGE) OF 23 KNOTS WITH GUSTS TO 33 KNOTS; THE CURRENT SLP VALUE IS 993.1MB, WHICH TYPICALLY CORRESPONDS TO A 35-40 KNOT TROPICAL CYCLONE, WITH A 24-HOUR SLP DECREASE OF 6.1MB. A 040215Z ASCAT-B IMAGE REVEALS AN EXTENSIVE SWATH OF 30-35 KNOT WINDS OVER WATER TO THE SOUTHWEST ASSOCIATED WITH A LARGE FIELD OF STABLE, COOL-AIR STRATOCUMULUS AS EVIDENT IN EIR. OVERALL, THIS DATA SUPPORTS THE INITIAL INTENSITY ASSESSMENT OF 35 KNOTS. ENVIRONMENTAL ANALYSIS INDICATES FAVORABLE UPPER-LEVEL CONDITIONS WITH LOW VERTICAL WIND SHEAR (VWS) AND POLEWARD VENTING INTO THE WESTERLIES TO THE SOUTH. HOWEVER, INTERACTION WITH LAND, DRY AIR ENTRAINMENT AND MARGINAL SST VALUES (25-26C) WILL HINDER DEVELOPMENT. TC 18S IS TRACKING ALONG THE NORTHERN PERIPHERY OF A LOW-LEVEL SUBTROPICAL RIDGE (STR) POSITIONED TO THE SOUTH BUT IS EXPECTED TO TURN SOUTHWARD AS A STR BUILDS EAST OF THE SYSTEM OVER WESTERN AUSTRALIA. DUE TO THE SOUTHWARD TRACK, THE SYSTEM WILL MOVE UNDER THE SUBTROPICAL WESTERLIES WITH INCREASING VWS (30-45 KNOTS), WHICH WILL LEAD TO STEADY WEAKENING AND EVENTUAL DISSIPATION BY TAU 36. NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT LENDING HIGH CONFIDENCE TO THE JTWC FORECAST TRACK, WHICH IS POSITIONED NEAR THE MULTI-MODEL CONSENSUS. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 041200Z IS 18 FEET. NEXT WARNINGS AT 042100Z, 050300Z, 050900Z AND 051500Z.// NNNN