WTXS31 PGTW 311500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/TROPICAL CYCLONE 18S (EIGHTEEN) WARNING NR 001// REF/A/JOINT TYPHOON WRNCEN PEARL HARBOR HI/301451ZJAN2021// AMPN/REF A IS A TROPICAL CYCLONE FORMATION ALERT.// RMKS/ 1. TROPICAL CYCLONE 18S (EIGHTEEN) WARNING NR 001 01 ACTIVE TROPICAL CYCLONE IN SOUTHIO MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE WIND RADII VALID OVER OPEN WATER ONLY --- WARNING POSITION: 311200Z --- NEAR 21.4S 121.1E MOVEMENT PAST SIX HOURS - 240 DEGREES AT 15 KTS POSITION ACCURATE TO WITHIN 060 NM POSITION BASED ON CENTER LOCATED BY SATELLITE PRESENT WIND DISTRIBUTION: MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT WIND RADII VALID OVER OPEN WATER ONLY REPEAT POSIT: 21.4S 121.1E --- FORECASTS: 12 HRS, VALID AT: 010000Z --- 21.5S 119.2E MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT WIND RADII VALID OVER OPEN WATER ONLY VECTOR TO 24 HR POSIT: 265 DEG/ 08 KTS --- 24 HRS, VALID AT: 011200Z --- 21.7S 117.4E MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT WIND RADII VALID OVER OPEN WATER ONLY VECTOR TO 36 HR POSIT: 255 DEG/ 09 KTS --- 36 HRS, VALID AT: 020000Z --- 22.2S 115.6E MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT WIND RADII VALID OVER OPEN WATER ONLY VECTOR TO 48 HR POSIT: 245 DEG/ 07 KTS --- EXTENDED OUTLOOK: 48 HRS, VALID AT: 021200Z --- 22.8S 114.2E MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT WIND RADII VALID OVER OPEN WATER ONLY VECTOR TO 72 HR POSIT: 275 DEG/ 04 KTS --- 72 HRS, VALID AT: 031200Z --- 22.7S 112.3E MAX SUSTAINED WINDS - 050 KT, GUSTS 065 KT WIND RADII VALID OVER OPEN WATER ONLY RADIUS OF 034 KT WINDS - 030 NM NORTHEAST QUADRANT 060 NM SOUTHEAST QUADRANT 060 NM SOUTHWEST QUADRANT 040 NM NORTHWEST QUADRANT VECTOR TO 96 HR POSIT: 270 DEG/ 03 KTS --- LONG RANGE OUTLOOK: --- 96 HRS, VALID AT: 041200Z --- 22.7S 111.1E MAX SUSTAINED WINDS - 045 KT, GUSTS 055 KT WIND RADII VALID OVER OPEN WATER ONLY RADIUS OF 034 KT WINDS - 110 NM NORTHEAST QUADRANT 070 NM SOUTHEAST QUADRANT 080 NM SOUTHWEST QUADRANT 100 NM NORTHWEST QUADRANT VECTOR TO 120 HR POSIT: 200 DEG/ 03 KTS --- 120 HRS, VALID AT: 051200Z --- 23.8S 110.7E MAX SUSTAINED WINDS - 040 KT, GUSTS 050 KT WIND RADII VALID OVER OPEN WATER ONLY RADIUS OF 034 KT WINDS - 170 NM NORTHEAST QUADRANT 100 NM SOUTHEAST QUADRANT 100 NM SOUTHWEST QUADRANT 130 NM NORTHWEST QUADRANT --- REMARKS: 311500Z POSITION NEAR 21.4S 120.6E. 31JAN21. TROPICAL CYCLONE (TC) 18S (EIGHTEEN), LOCATED APPROXIMATELY 394 NM EAST OF LEARMONTH, AUSTRALIA, HAS TRACKED WEST-SOUTHWESTWARD AT 15 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS SPIRAL BANDS OF CONVECTION WRAPPING INTO A WELL DEFINED MID-LEVEL CIRCULATION CENTER. THE INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE BASED ON THE CONVECTIVE FEATURES IN THE EIR LOOP. THE INITIAL INTENSITY IS ASSESSED AT 30 KTS BASED ON MULTIPLE SURFACE OBSERVATIONS SURROUNDING THE SYSTEM CENTER WITH OVERALL FAIR CONFIDENCE. TC 18S IS TRACKING OVER LAND THROUGH WESTERN AUSTRALIA, HOWEVER THE ENVIRONMENT IS OVERALL MARGINALLY FAVORABLE WITH LOW (10-15 KTS) VERTICAL WIND SHEAR (VWS) AND MODERATE UPPER LEVEL OUTFLOW ALOFT. THE PRIMARY STEERING MECHANISM IS A SUBTROPICAL RIDGE (STR) POSITIONED TO THE SOUTHWEST, IN ADDITION TO A SECONDARY STR TO THE EAST. TC 18S IS FORECAST TO CONTINUE TRACKING OVER WESTERN AUSTRALIA AND INTENSIFY ONLY MINIMALLY TO 35 KTS BY TAU 48, AT WHICH POINT IT WILL BE APPROXIMATELY 40 NM SOUTH OF LEARMONTH, AUSTRALIA. THEREAFTER, THE SYSTEM WILL ENTER THE WARM WATERS OF THE SOUTH INDIAN OCEAN. WARM (27-28 CELSIUS) SEA SURFACE TEMPERATURES, COUPLED WITH CONTINUED LOW VWS AND MODERATE UPPER LEVEL SUPPORT, WILL LEAD TO GRADUAL INTENSIFICATION TO A PEAK INTENSITY OF 50 KTS BY TAU 72. THEREAFTER, MODERATE (20-25) VWS AND COOLER SST WILL LEAD TO A GRADUAL WEAKENING TREND WITH TC 18S TRACKING SOUTHWARD AFTER TAU 96 ALONG THE WESTERN PERIPHERY OF THE STEERING STR TO THE EAST. NUMERICAL MODEL SOLUTIONS ARE IN GOOD AGREEMENT ON THE GENERALLY WESTWARD TRACK THROUGH TAU 96 BUT DIVERGE SLIGHTLY ON THE TIMING OF THE SOUTHWARD TURN THEREAFTER. THIS GOOD AGREEMENT IN NUMERICAL MODEL SOLUTIONS LENDS OVERALL HIGH CONFIDENCE IN THE JTWC FORECAST TRACK WHICH IS PLACED ON THE MULTI-MODEL CONSENSUS. NEXT WARNINGS AT 312100Z, 010300Z, 010900Z AND 011500Z. 2. THIS CANCELS AND SUPERSEDES REF A (WTXS21 PGTW 301500).// NNNN