WTXS51 PGTW 040300 WARNING ATCG MIL 18S SIO 210204013458 2021020400 18S EIGHTEEN 015 01 220 07 SATL RADR SYNP 030 T000 243S 1143E 030 T012 247S 1135E 030 T024 251S 1129E 035 R034 000 NE QD 010 SE QD 100 SW QD 030 NW QD T036 259S 1125E 035 R034 000 NE QD 070 SE QD 100 SW QD 030 NW QD T048 277S 1127E 030 AMP 036HR DISSIPATING AS A SIGNIFICANT TROPICAL CYCLONE OVER WATER 048HR DISSIPATED AS A SIGNIFICANT TROPICAL CYCLONE OVER WATER SUBJ: TROPICAL CYCLONE 18S (EIGHTEEN) WARNING NR 015 1. TROPICAL CYCLONE 18S (EIGHTEEN) WARNING NR 015 01 ACTIVE TROPICAL CYCLONE IN SOUTHIO MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE WIND RADII VALID OVER OPEN WATER ONLY --- WARNING POSITION: 040000Z --- NEAR 24.3S 114.3E MOVEMENT PAST SIX HOURS - 220 DEGREES AT 07 KTS POSITION ACCURATE TO WITHIN 030 NM POSITION BASED ON CENTER LOCATED BY A COMBINATION OF SATELLITE, RADAR AND SYNOPTIC DATA PRESENT WIND DISTRIBUTION: MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT WIND RADII VALID OVER OPEN WATER ONLY REPEAT POSIT: 24.3S 114.3E --- FORECASTS: 12 HRS, VALID AT: 041200Z --- 24.7S 113.5E MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT WIND RADII VALID OVER OPEN WATER ONLY VECTOR TO 24 HR POSIT: 235 DEG/ 03 KTS --- 24 HRS, VALID AT: 050000Z --- 25.1S 112.9E MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT WIND RADII VALID OVER OPEN WATER ONLY RADIUS OF 034 KT WINDS - 000 NM NORTHEAST QUADRANT 010 NM SOUTHEAST QUADRANT 100 NM SOUTHWEST QUADRANT 030 NM NORTHWEST QUADRANT VECTOR TO 36 HR POSIT: 205 DEG/ 04 KTS --- 36 HRS, VALID AT: 051200Z --- 25.9S 112.5E 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 070 NM SOUTHEAST QUADRANT 100 NM SOUTHWEST QUADRANT 030 NM NORTHWEST QUADRANT VECTOR TO 48 HR POSIT: 175 DEG/ 09 KTS --- EXTENDED OUTLOOK: 48 HRS, VALID AT: 060000Z --- 27.7S 112.7E MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT WIND RADII VALID OVER OPEN WATER ONLY DISSIPATED AS A SIGNIFICANT TROPICAL CYCLONE OVER WATER --- REMARKS: 040300Z POSITION NEAR 24.4S 114.1E. 04FEB21. TROPICAL CYCLONE 18S (EIGHTEEN), LOCATED APPROXIMATELY 121 NM SOUTH OF LEARMONTH, AUSTRALIA, HAS TRACKED SOUTHWESTWARD AT 07 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS WEAKENING CONVECTION SHEARED TO THE EAST OF AN EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) LOCATED JUST NORTH OF CARNARVON. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC, SUPPORTED BY ANIMATED COMPOSITE RADAR DATA FROM CARNARVON. THE INITIAL INTENSITY IS ALSO ASSESSED WITH HIGH CONFIDENCE BASED ON SURFACE OBSERVATION DATA FROM CARNARVON WHICH INDICATED SUSTAINED WINDS BETWEEN 25-30 KTS WITH GUSTS ABOUT 35 KTS. THE SYSTEM LIES IN A GENERALLY MARGINAL TO SLIGHTLY FAVORABLE ENVIRONMENT CHARACTERIZED BY LOW (10-15 KT) VWS AND ROBUST POLEWARD OUTFLOW. HOWEVER, THE ANIMATED MSI SHOWS A BROAD AREA OF RELATIVELY STABLE STRATOCUMULUS FIELD EXTENDING FAR TO THE WEST OF THE AUSTRALIAN COAST AND WRAPPING INTO THE SYSTEM, WHICH WILL LIKELY SERVE AS A HINDRANCE TO MUCH ADDITIONAL DEVELOPMENT. THE SYSTEM HAS NOW STARTED ACCELERATING TO THE SOUTHWEST ALONG THE WESTERN PERIPHERY OF A DEEP-LAYER STR LOCATED TO THE NORTHEAST AND WILL ROUND THE RIDGE AXIS BY TAU 36 BEFORE TURNING TO THE SOUTH. SSTS IN THE AREA JUST OFFSHORE ARE ABOUT 26C, WHICH SHOULD ALLOW FOR A SLIGHT INTENSIFICATION TO 35 KNOTS BY TAU 24. THEREAFTER, RAPIDLY INCREASING WESTERLY VWS AND DECREASING SSTS (<25C) WILL QUICKLY WEAKEN THE SYSTEM, LEADING TO FULL DISSIPATION AS A TROPICAL CYCLONE BY TAU 48. NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT WITH INCREASING UNCERTAINTY AFTER TAU 12 AS THE CONSENSUS MEMBERS DISAGREE ON THE EXACT TIMING OF THE TURN TOWARDS THE SOUTH, LEADING TO A SPREAD OF 122NM BY TAU 48. THE JTWC FORECAST LIES FASTER AND TO THE LEFT OF THE MULTI-MODEL CONSENSUS WITH LOW CONFIDENCE. NEXT WARNINGS AT 040900Z, 041500Z, 042100Z AND 050300Z. // 1821012818 159S1266E 15 1821012900 164S1261E 15 1821012906 168S1258E 20 1821012912 172S1256E 20 1821012918 176S1254E 20 1821013000 179S1251E 25 1821013006 183S1246E 30 1821013012 187S1240E 30 1821013018 192S1235E 30 1821013100 201S1229E 30 1821013106 210S1223E 30 1821013112 214S1211E 30 1821013118 213S1202E 30 1821020100 207S1194E 30 1821020106 206S1190E 30 1821020112 211S1181E 30 1821020118 215S1171E 30 1821020200 222S1163E 30 1821020206 229S1157E 30 1821020212 236S1151E 30 1821020218 240S1145E 30 1821020300 238S1144E 30 1821020306 239S1143E 30 1821020312 238S1144E 30 1821020318 238S1148E 30 1821020400 243S1143E 30 NNNN