WTPS31 PGTW 180900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/TROPICAL CYCLONE 05P (YASA) WARNING NR 024// RMKS/ 1. TROPICAL CYCLONE 05P (YASA) WARNING NR 024 01 ACTIVE TROPICAL CYCLONE IN SOUTHPAC MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE WIND RADII VALID OVER OPEN WATER ONLY --- WARNING POSITION: 180600Z --- NEAR 19.1S 178.3W MOVEMENT PAST SIX HOURS - 145 DEGREES AT 10 KTS POSITION ACCURATE TO WITHIN 040 NM POSITION BASED ON CENTER LOCATED BY SATELLITE PRESENT WIND DISTRIBUTION: MAX SUSTAINED WINDS - 075 KT, GUSTS 090 KT WIND RADII VALID OVER OPEN WATER ONLY RADIUS OF 064 KT WINDS - 050 NM NORTHEAST QUADRANT 055 NM SOUTHEAST QUADRANT 040 NM SOUTHWEST QUADRANT 040 NM NORTHWEST QUADRANT RADIUS OF 050 KT WINDS - 095 NM NORTHEAST QUADRANT 105 NM SOUTHEAST QUADRANT 080 NM SOUTHWEST QUADRANT 065 NM NORTHWEST QUADRANT RADIUS OF 034 KT WINDS - 175 NM NORTHEAST QUADRANT 185 NM SOUTHEAST QUADRANT 145 NM SOUTHWEST QUADRANT 125 NM NORTHWEST QUADRANT REPEAT POSIT: 19.1S 178.3W --- FORECASTS: 12 HRS, VALID AT: 181800Z --- 20.3S 177.5W MAX SUSTAINED WINDS - 065 KT, GUSTS 080 KT WIND RADII VALID OVER OPEN WATER ONLY RADIUS OF 064 KT WINDS - 010 NM NORTHEAST QUADRANT 030 NM SOUTHEAST QUADRANT 020 NM SOUTHWEST QUADRANT 000 NM NORTHWEST QUADRANT RADIUS OF 050 KT WINDS - 050 NM NORTHEAST QUADRANT 060 NM SOUTHEAST QUADRANT 050 NM SOUTHWEST QUADRANT 030 NM NORTHWEST QUADRANT RADIUS OF 034 KT WINDS - 140 NM NORTHEAST QUADRANT 150 NM SOUTHEAST QUADRANT 130 NM SOUTHWEST QUADRANT 090 NM NORTHWEST QUADRANT VECTOR TO 24 HR POSIT: 165 DEG/ 06 KTS --- 24 HRS, VALID AT: 190600Z --- 21.4S 177.2W MAX SUSTAINED WINDS - 060 KT, GUSTS 075 KT WIND RADII VALID OVER OPEN WATER ONLY BECOMING SUBTROPICAL RADIUS OF 050 KT WINDS - 040 NM NORTHEAST QUADRANT 060 NM SOUTHEAST QUADRANT 050 NM SOUTHWEST QUADRANT 030 NM NORTHWEST QUADRANT RADIUS OF 034 KT WINDS - 120 NM NORTHEAST QUADRANT 140 NM SOUTHEAST QUADRANT 120 NM SOUTHWEST QUADRANT 080 NM NORTHWEST QUADRANT VECTOR TO 36 HR POSIT: 180 DEG/ 05 KTS --- 36 HRS, VALID AT: 191800Z --- 22.4S 177.2W MAX SUSTAINED WINDS - 055 KT, GUSTS 070 KT WIND RADII VALID OVER OPEN WATER ONLY BECOMING SUBTROPICAL RADIUS OF 050 KT WINDS - 030 NM NORTHEAST QUADRANT 040 NM SOUTHEAST QUADRANT 030 NM SOUTHWEST QUADRANT 020 NM NORTHWEST QUADRANT RADIUS OF 034 KT WINDS - 090 NM NORTHEAST QUADRANT 140 NM SOUTHEAST QUADRANT 110 NM SOUTHWEST QUADRANT 070 NM NORTHWEST QUADRANT VECTOR TO 48 HR POSIT: 205 DEG/ 04 KTS --- EXTENDED OUTLOOK: 48 HRS, VALID AT: 200600Z --- 23.2S 177.6W MAX SUSTAINED WINDS - 050 KT, GUSTS 065 KT WIND RADII VALID OVER OPEN WATER ONLY BECOMING SUBTROPICAL RADIUS OF 050 KT WINDS - 020 NM NORTHEAST QUADRANT 040 NM SOUTHEAST QUADRANT 030 NM SOUTHWEST QUADRANT 010 NM NORTHWEST QUADRANT RADIUS OF 034 KT WINDS - 080 NM NORTHEAST QUADRANT 130 NM SOUTHEAST QUADRANT 110 NM SOUTHWEST QUADRANT 060 NM NORTHWEST QUADRANT VECTOR TO 72 HR POSIT: 205 DEG/ 04 KTS --- 72 HRS, VALID AT: 210600Z --- 24.7S 178.4W MAX SUSTAINED WINDS - 045 KT, GUSTS 055 KT WIND RADII VALID OVER OPEN WATER ONLY SUBTROPICAL RADIUS OF 034 KT WINDS - 070 NM NORTHEAST QUADRANT 120 NM SOUTHEAST QUADRANT 100 NM SOUTHWEST QUADRANT 060 NM NORTHWEST QUADRANT --- REMARKS: 180900Z POSITION NEAR 19.4S 178.1W. 18DEC20. TROPICAL CYCLONE (TC) 05P (YASA), LOCATED APPROXIMATELY 197 NM EAST-SOUTHEAST OF SUVA, FIJI, HAS TRACKED SOUTHEASTWARD AT 10 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS AN ELONGATED CIRCULATION WITH DEEP CONVECTION SHEARED OVER THE SOUTHEASTERN SEMICIRCLE. THE INITIAL POSITION IS SUPPORTED BY LOW LEVEL BANDING IN THE MSI LOOP AND IN 180413Z SSMIS 37GHZ AND 180633Z AMSU 89 GHZ IMAGES. THE INITIAL INTENSITY OF 75 KNOTS IS ASSESSED WITH MODERATE CONFIDENCE BASED ON MULTI-AGENCY DVORAK CURRENT INTENSITY ESTIMATES OF T4.5 (77 KTS, PGTW, NFFN AND KNES). ENVIRONMENTAL ANALYSIS REVEALS A MARGINAL ENVIRONMENT CHARACTERIZED BY WARM(27- 28C) SEA SURFACE TEMPERATURES (SST) AND ROBUST POLEWARD OUTFLOW ALOFT, OFFSET BY MODERATE (15-25 KTS) VERTICAL WIND SHEAR (VWS), AND CONVERGENT UPPER LEVEL FLOW ALONG THE NORTHERN PERIPHERY OF THE SYSTEM. THE SYSTEM IS TRACKING ALONG THE PERIPHERY OF A SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST. IN THE NEAR TERM, THE STEERING RIDGE WILL REPOSITION DUE TO INTERACTION WITH AN AMPLIFYING MIDLATITUDE TROUGH POSITIONED TO THE SOUTHWEST. THIS INTERACTION, COUPLED WITH THE BUILDING OF A STRONG TRANSITORY RIDGE NORTH OF NEW ZEALAND, WILL CAUSE THE STORM TRACK TO BECOME SOUTHWARD AFTER TAU 12 AND THEN SOUTHWESTWARD THEREAFTER. ENVIRONMENTAL CONDITIONS WILL CONTINUE TO DEGRADE THROUGHOUT THE REMAINDER OF THE FORECAST PERIOD WITH INCREASING VWS TO 30+ KTS BY TAU 24 AND COOL (< 26 CELSIUS) SST BY TAU 36. AS A RESULT, TC YASA WILL WEAKEN AND BEGIN SUBTROPICAL TRANSITION BY TAU 24. THEREAFTER, THE SYSTEM WILL CONTINUE TO WEAKEN AS THE WIND FIELD EXPANDS AND BECOMES ASYMMETRIC AND BY TAU 72, TC YASA WILL COMPLETE SUBTROPICAL TRANSITION. NUMERICAL MODEL GUIDANCE REMAINS IN TIGHT AGREEMENT THROUGH TAU 24. THEREAFTER, THE SPREAD IN NUMERICAL MODEL SOLUTIONS BEGINS TO INCREASE WITH A BIFURCATION OF MODEL TRACKS OCCURRING THEREAFTER. THE GFS, GALWEM, AND ECMWF MODELS CONVERGE ON A WESTWARD RECURVE, WHILE THE UKMET AND NAVGEM SOLUTIONS BRING THE VORTEX EASTWARD AFTER TAU 24. THIS BIFURCATION IN MODEL SOLUTIONS LENDS OVERALL LOW CONFIDENCE IN THE JTWC FORCAST TRACK AFTER TAU 24 WHICH IS PLACED SLIGHTLY EAST OF THE MULTI-MODEL CONSENSUS. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 180600Z IS 26 FEET. NEXT WARNINGS AT 181500, 182100Z, 190300 AND 190900Z. // NNNN