WTXS31 PGTW 040900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/TROPICAL CYCLONE 18S (EIGHTEEN) WARNING NR 016// RMKS/ 1. TROPICAL CYCLONE 18S (EIGHTEEN) WARNING NR 016 01 ACTIVE TROPICAL CYCLONE IN SOUTHIO MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE WIND RADII VALID OVER OPEN WATER ONLY --- WARNING POSITION: 040600Z --- NEAR 24.4S 113.7E MOVEMENT PAST SIX HOURS - 260 DEGREES AT 06 KTS POSITION ACCURATE TO WITHIN 020 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: 24.4S 113.7E --- FORECASTS: 12 HRS, VALID AT: 041800Z --- 24.5S 113.1E MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT WIND RADII VALID OVER OPEN WATER ONLY RADIUS OF 034 KT WINDS - 000 NM NORTHEAST QUADRANT 020 NM SOUTHEAST QUADRANT 080 NM SOUTHWEST QUADRANT 000 NM NORTHWEST QUADRANT VECTOR TO 24 HR POSIT: 220 DEG/ 03 KTS --- 24 HRS, VALID AT: 050600Z --- 24.9S 112.7E MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT WIND RADII VALID OVER OPEN WATER ONLY RADIUS OF 034 KT WINDS - 000 NM NORTHEAST QUADRANT 060 NM SOUTHEAST QUADRANT 080 NM SOUTHWEST QUADRANT 010 NM NORTHWEST QUADRANT VECTOR TO 36 HR POSIT: 180 DEG/ 06 KTS --- 36 HRS, VALID AT: 051800Z --- 26.1S 112.7E 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 - 020 NM NORTHEAST QUADRANT 120 NM SOUTHEAST QUADRANT 100 NM SOUTHWEST QUADRANT 030 NM NORTHWEST QUADRANT VECTOR TO 48 HR POSIT: 165 DEG/ 08 KTS --- EXTENDED OUTLOOK: 48 HRS, VALID AT: 060600Z --- 27.6S 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: 040900Z POSITION NEAR 24.4S 113.6E. 04FEB21. TROPICAL CYCLONE (TC) 18S (EIGHTEEN), LOCATED APPROXIMATELY 128 NM SOUTH OF LEARMONTH, AUSTRALIA, HAS TRACKED WESTWARD AT 06 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS LOW-LEVEL CLOUD LINES WRAPPING TIGHTLY INTO A WELL-DEFINED LOW-LEVEL CIRCULATION CENTER, WHICH SUPPORTS THE INITIAL POSITION WITH GOOD CONFIDENCE. ANIMATED RADAR IMAGERY FROM THE CARNARVON RADAR INDICATES THE BULK OF THE CONVECTIVE BANDING IS OVER LAND, OVER THE SOUTHERN SEMICIRCLE. THE CENTER IS LOCATED APPROXIMATELY 30NM NORTH OF CARNARVON, WHICH IS REPORTING SUSTAINED SURFACE WINDS (10-MINUTE AVERAGE) OF 24-27 KNOTS WITH GUSTS AS HIGH AS 37 KNOTS; THE MINIMUM SLP THUS FAR IS 991.8MB, WHICH TYPICALLY CORRESPONDS TO A 35-40 KNOT TROPICAL CYCLONE, WITH A 24-HOUR DECREASE OF 5.0MB. 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 MSI. 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 (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 48. WITH THE EXCEPTION OF NAVGEM, 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 040600Z IS 18 FEET. NEXT WARNINGS AT 041500Z, 042100Z, 050300Z AND 050900Z.// NNNN