WTPS31 PGTW 280900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/TROPICAL CYCLONE 04P (TUNI) WARNING NR 003// RMKS/ 1. TROPICAL CYCLONE 04P (TUNI) WARNING NR 003 01 ACTIVE TROPICAL CYCLONE IN SOUTHPAC MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE WIND RADII VALID OVER OPEN WATER ONLY --- WARNING POSITION: 280600Z --- NEAR 14.2S 173.4W MOVEMENT PAST SIX HOURS - 115 DEGREES AT 11 KTS POSITION ACCURATE TO WITHIN 060 NM POSITION BASED ON CENTER LOCATED BY SATELLITE PRESENT WIND DISTRIBUTION: MAX SUSTAINED WINDS - 040 KT, GUSTS 050 KT WIND RADII VALID OVER OPEN WATER ONLY RADIUS OF 034 KT WINDS - 065 NM NORTHEAST QUADRANT 055 NM SOUTHEAST QUADRANT 055 NM SOUTHWEST QUADRANT 065 NM NORTHWEST QUADRANT REPEAT POSIT: 14.2S 173.4W --- FORECASTS: 12 HRS, VALID AT: 281800Z --- 15.3S 171.8W MAX SUSTAINED WINDS - 045 KT, GUSTS 055 KT WIND RADII VALID OVER OPEN WATER ONLY RADIUS OF 034 KT WINDS - 075 NM NORTHEAST QUADRANT 065 NM SOUTHEAST QUADRANT 065 NM SOUTHWEST QUADRANT 075 NM NORTHWEST QUADRANT VECTOR TO 24 HR POSIT: 135 DEG/ 09 KTS --- 24 HRS, VALID AT: 290600Z --- 16.5S 170.5W MAX SUSTAINED WINDS - 045 KT, GUSTS 055 KT WIND RADII VALID OVER OPEN WATER ONLY RADIUS OF 034 KT WINDS - 090 NM NORTHEAST QUADRANT 075 NM SOUTHEAST QUADRANT 075 NM SOUTHWEST QUADRANT 090 NM NORTHWEST QUADRANT VECTOR TO 36 HR POSIT: 140 DEG/ 09 KTS --- 36 HRS, VALID AT: 291800Z --- 17.8S 169.3W MAX SUSTAINED WINDS - 045 KT, GUSTS 055 KT WIND RADII VALID OVER OPEN WATER ONLY BECOMING EXTRATROPICAL RADIUS OF 034 KT WINDS - 085 NM NORTHEAST QUADRANT 085 NM SOUTHEAST QUADRANT 070 NM SOUTHWEST QUADRANT 070 NM NORTHWEST QUADRANT VECTOR TO 48 HR POSIT: 145 DEG/ 10 KTS --- EXTENDED OUTLOOK: 48 HRS, VALID AT: 300600Z --- 19.4S 168.1W MAX SUSTAINED WINDS - 040 KT, GUSTS 050 KT WIND RADII VALID OVER OPEN WATER ONLY EXTRATROPICAL --- REMARKS: 280900Z POSITION NEAR 14.5S 173.0W. TROPICAL CYCLONE (TC) 04P (TUNI), LOCATED APPROXIMATELY 157 NM WEST OF PAGO PAGO, AMERICAN SAMOA HAS TRACKED EAST-SOUTHEASTWARD AT 11 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS AN ELONGATED CLOUD STRUCTURE WITH A SLIGHT INCREASE IN CENTRAL CONVECTION AND SIGNIFICANT BROKEN CONVECTIVE BANDING WRAPPING INTO THE CENTER FROM THE NORTHERN PERIPHERY. A 280641Z SSMIS 91GHZ MICROWAVE IMAGE SHOWS THAT ALL SIGNIFICANT CENTRAL CONVECTION IS BEING SHEARED ALONG THE SOUTHEASTERN PERIPHERY DUE TO THE MODERATE NORTHWESTERLY VERTICAL WIND SHEAR (VWS) ASSOCIATED WITH A HIGH AMPLITUDE MID-LATITUDE TROUGH TO THE WEST. ADDITIONALLY, THE TROUGH IS PROVIDING AN ENHANCED POLEWARD OUTFLOW CHANNEL THAT IS SUSTAINING THE CURRENT CONVECTION. THE INITIAL POSITION IS BASED ON THE AFOREMENTIONED IMAGERY AS WELL AS A 280512Z AMSU-B 89GHZ MICROWAVE IMAGE WITH FAIR CONFIDENCE. THE INTENSITY HAS BEEN HELD AT 40 KNOTS BASED ON A PREVIOUS ASCAT PASS SHOWING 40 KNOT WINDS AND UNCHANGED DVORAK INTENSITY ESTIMATES FROM PGTW, PHFO, AND ABRF. TC 04P IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A NEAR- EQUATORIAL RIDGE (NER). THE NER WILL REMAIN THE DOMINANT STEERING MECHANISM OVER THE NEXT 12 TO 24 HOURS, PRIOR TO THE SYSTEM TRANSITIONING TO A BUILDING SUB-TROPICAL RIDGE TO THE SOUTHEAST. TC TUNI WILL STRENGTHEN SLIGHTLY DUE TO THE ENHANCED OUTFLOW CHANNEL; HOWEVER, THE INCREASING VWS ASSOCIATED WITH THE STRONG MID-LATITUDE WESTERLY WIND FLOW WILL HAMPER ANY SIGNIFICANT INTENSIFICATION. IN ADDITION, SEA SURFACE TEMPERATURES WILL CONTINUE TO DROP OFF AS THE CYCLONE GAINS LATITUDE. TC 04P WILL BEGIN TO EMBED WITHIN THE BAROCLINIC ZONE AND START EXTRA-TROPICAL TRANSITION (ETT) BY TAU 36 AND COMPLETE ETT BY THE END OF THE FORECAST PERIOD AS THE SYSTEM GAINS FRONTAL CHARACTERISTICS. DYNAMIC MODEL GUIDANCE REMAINS MOSTLY UNCHANGED WITH NVGM AND GFDN REMAINING SIGNIFICANTLY SLOW AND WESTERN OUTLIERS. BASED ON THE FORECASTED MID-LATITUDE PATTERN AND ASSOCIATED STEERING FLOW, THIS SOLUTION SEEMS UNLIKELY. HOWEVER, DUE TO THE CONTINUED SPREAD IN MODEL GUIDANCE AND THE BROAD NATURE OF THE CYCLONE, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 280600Z IS 13 FEET. NEXT WARNINGS AT 281500Z, 282100Z, 290300Z AND 290900Z.//