• Pacific-SW: Yasa W21

    From Weather Alert@21:1/175 to All on Thursday, December 17, 2020 14:24:00
    WTPS31 PGTW 171500
    MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
    SUBJ/TROPICAL CYCLONE 05P (YASA) WARNING NR 021//
    RMKS/
    1. TROPICAL CYCLONE 05P (YASA) WARNING NR 021
    01 ACTIVE TROPICAL CYCLONE IN SOUTHPAC
    MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
    WIND RADII VALID OVER OPEN WATER ONLY
    ---
    WARNING POSITION:
    171200Z --- NEAR 17.2S 179.9W
    MOVEMENT PAST SIX HOURS - 120 DEGREES AT 14 KTS
    POSITION ACCURATE TO WITHIN 050 NM
    POSITION BASED ON CENTER LOCATED BY A COMBINATION OF
    SATELLITE AND RADAR
    PRESENT WIND DISTRIBUTION:
    MAX SUSTAINED WINDS - 115 KT, GUSTS 140 KT
    WIND RADII VALID OVER OPEN WATER ONLY
    RADIUS OF 064 KT WINDS - 055 NM NORTHEAST QUADRANT
    050 NM SOUTHEAST QUADRANT
    045 NM SOUTHWEST QUADRANT
    045 NM NORTHWEST QUADRANT
    RADIUS OF 050 KT WINDS - 100 NM NORTHEAST QUADRANT
    095 NM SOUTHEAST QUADRANT
    085 NM SOUTHWEST QUADRANT
    080 NM NORTHWEST QUADRANT
    RADIUS OF 034 KT WINDS - 175 NM NORTHEAST QUADRANT
    170 NM SOUTHEAST QUADRANT
    155 NM SOUTHWEST QUADRANT
    145 NM NORTHWEST QUADRANT
    REPEAT POSIT: 17.2S 179.9W
    ---
    FORECASTS:
    12 HRS, VALID AT:
    180000Z --- 18.4S 178.3W
    MAX SUSTAINED WINDS - 105 KT, GUSTS 130 KT
    WIND RADII VALID OVER OPEN WATER ONLY
    RADIUS OF 064 KT WINDS - 030 NM NORTHEAST QUADRANT
    030 NM SOUTHEAST QUADRANT
    030 NM SOUTHWEST QUADRANT
    030 NM NORTHWEST QUADRANT
    RADIUS OF 050 KT WINDS - 070 NM NORTHEAST QUADRANT
    070 NM SOUTHEAST QUADRANT
    060 NM SOUTHWEST QUADRANT
    060 NM NORTHWEST QUADRANT
    RADIUS OF 034 KT WINDS - 160 NM NORTHEAST QUADRANT
    170 NM SOUTHEAST QUADRANT
    140 NM SOUTHWEST QUADRANT
    130 NM NORTHWEST QUADRANT
    VECTOR TO 24 HR POSIT: 150 DEG/ 09 KTS
    ---
    24 HRS, VALID AT:
    181200Z --- 19.9S 177.3W
    MAX SUSTAINED WINDS - 095 KT, GUSTS 115 KT
    WIND RADII VALID OVER OPEN WATER ONLY
    RADIUS OF 064 KT WINDS - 020 NM NORTHEAST QUADRANT
    030 NM SOUTHEAST QUADRANT
    030 NM SOUTHWEST QUADRANT
    020 NM NORTHWEST QUADRANT
    RADIUS OF 050 KT WINDS - 060 NM NORTHEAST QUADRANT
    060 NM SOUTHEAST QUADRANT
    060 NM SOUTHWEST QUADRANT
    050 NM NORTHWEST QUADRANT
    RADIUS OF 034 KT WINDS - 150 NM NORTHEAST QUADRANT
    160 NM SOUTHEAST QUADRANT
    140 NM SOUTHWEST QUADRANT
    100 NM NORTHWEST QUADRANT
    VECTOR TO 36 HR POSIT: 160 DEG/ 07 KTS
    ---
    36 HRS, VALID AT:
    190000Z --- 21.2S 176.8W
    MAX SUSTAINED WINDS - 085 KT, GUSTS 105 KT
    WIND RADII VALID OVER OPEN WATER ONLY
    RADIUS OF 064 KT WINDS - 020 NM NORTHEAST QUADRANT
    020 NM SOUTHEAST QUADRANT
    030 NM SOUTHWEST QUADRANT
    010 NM NORTHWEST QUADRANT
    RADIUS OF 050 KT WINDS - 050 NM NORTHEAST QUADRANT
    060 NM SOUTHEAST QUADRANT
    060 NM SOUTHWEST QUADRANT
    040 NM NORTHWEST QUADRANT
    RADIUS OF 034 KT WINDS - 130 NM NORTHEAST QUADRANT
    150 NM SOUTHEAST QUADRANT
    130 NM SOUTHWEST QUADRANT
    090 NM NORTHWEST QUADRANT
    VECTOR TO 48 HR POSIT: 190 DEG/ 06 KTS
    ---
    EXTENDED OUTLOOK:
    48 HRS, VALID AT:
    191200Z --- 22.4S 177.0W
    MAX SUSTAINED WINDS - 070 KT, GUSTS 085 KT
    WIND RADII VALID OVER OPEN WATER ONLY
    RADIUS OF 064 KT WINDS - 020 NM NORTHEAST QUADRANT
    020 NM SOUTHEAST QUADRANT
    020 NM SOUTHWEST QUADRANT
    010 NM NORTHWEST QUADRANT
    RADIUS OF 050 KT WINDS - 040 NM NORTHEAST QUADRANT
    060 NM SOUTHEAST QUADRANT
    060 NM SOUTHWEST QUADRANT
    040 NM NORTHWEST QUADRANT
    RADIUS OF 034 KT WINDS - 120 NM NORTHEAST QUADRANT
    140 NM SOUTHEAST QUADRANT
    130 NM SOUTHWEST QUADRANT
    080 NM NORTHWEST QUADRANT
    VECTOR TO 72 HR POSIT: 215 DEG/ 04 KTS
    ---
    72 HRS, VALID AT:
    201200Z --- 23.7S 178.0W
    MAX SUSTAINED WINDS - 045 KT, GUSTS 055 KT
    WIND RADII VALID OVER OPEN WATER ONLY
    BECOMING SUBTROPICAL
    RADIUS OF 034 KT WINDS - 090 NM NORTHEAST QUADRANT
    140 NM SOUTHEAST QUADRANT
    120 NM SOUTHWEST QUADRANT
    070 NM NORTHWEST QUADRANT
    VECTOR TO 96 HR POSIT: 235 DEG/ 06 KTS
    ---
    LONG RANGE OUTLOOK:
    ---
    96 HRS, VALID AT:
    211200Z --- 25.1S 179.7E
    MAX SUSTAINED WINDS - 040 KT, GUSTS 050 KT
    WIND RADII VALID OVER OPEN WATER ONLY
    SUBTROPICAL
    RADIUS OF 034 KT WINDS - 090 NM NORTHEAST QUADRANT
    140 NM SOUTHEAST QUADRANT
    120 NM SOUTHWEST QUADRANT
    070 NM NORTHWEST QUADRANT
    VECTOR TO 120 HR POSIT: 250 DEG/ 06 KTS
    ---
    120 HRS, VALID AT:
    221200Z --- 25.9S 177.2E
    MAX SUSTAINED WINDS - 040 KT, GUSTS 050 KT
    WIND RADII VALID OVER OPEN WATER ONLY
    SUBTROPICAL
    RADIUS OF 034 KT WINDS - 090 NM NORTHEAST QUADRANT
    140 NM SOUTHEAST QUADRANT
    120 NM SOUTHWEST QUADRANT
    070 NM NORTHWEST QUADRANT
    ---
    REMARKS:
    171500Z POSITION NEAR 17.5S 179.5W.
    17DEC20. TROPICAL CYCLONE 05P (YASA), LOCATED APPROXIMATELY 111
    NM EAST-NORTHEAST OF SUVA, FIJI, HAS TRACKED EAST-SOUTHEASTWARD
    AT 14 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED
    (EIR) SATELLITE IMAGERY DEPICTS A DRAMATICALLY WEAKENED SYSTEM, WITH
    THE PREVIOUSLY WELL ESTABLISHED EYE HAVING FULLY FILLED IN AND
    DISSIPATED BY THE 0600Z HOUR, AFTER PASSING OVER THE ISLAND OF VANUA
    LEVU. THE INITIAL POSITION IS PLACED WITH MODERATE CONFIDENCE DUE TO
    THE OBSCURED NATURE OF THE LOW-LEVEL CIRCULATION CENTER (LLCC) AND
    THE LACK OF ANY RECENT MICROWAVE IMAGERY. FIJI RADAR DATA WAS NOT
    CONCLUSIVE, BUT DID PROVIDE SOME ADDITIONAL CLARITY TO THE INITIAL
    POSITION. THE INITIAL INTENSITY IS ASSESSED AT 115 KNOTS BASED ON A
    PGTW/KNES DVORAK CURRENT INTENSITY ESTIMATES OF T6.0 (115 KTS), AND
    AN ADVANCED DVORAK TECHNIQUE (ADT) ESTIMATE OF T5.5 (102 KTS). UPPER-
    LEVEL ANALYSIS INDICATES RADIAL OUTFLOW WITH ENHANCED, BUT
    WEAKENING, POLEWARD OUTFLOW INTO THE MID-LATITUDE WESTERLIES TO THE
    SOUTH, WITH MODERATE (15-25 KTS) VWS. SEA SURFACE TEMPERATURES
    REMAIN WARM (27-28C). TC 05P IS FORECAST TO CONTINUE TRACKING
    SOUTHEASTWARD THROUGH TAU 24 UNDER THE STEERING INFLUENCE OF THE
    DEEP-LAYER NEAR EQUATORIAL-SUBTROPICAL RIDGE (NER-STR) COMPLEX
    LOCATED TO THE EAST. AFTER TAU 24, A RELATIVELY STRONG MID-LATITUDE
    TROUGH WILL PASS BY TO THE SOUTH, WEAKENING THE STEERING RIDGE TO
    THE EAST, ALLOWING FOR THE SYSTEM TO SLOW DOWN AND TURN SOUTH
    THROUGH TAU 48. THEREAFTER ANOTHER STR DEVELOPS AND BUILDS NORTH OF
    THE NEW ZEALAND, BECOMING THE DOMINATE STEERING MECHANISM AND
    PUSHING TC 05P ONTO A SOUTHWESTWARD TRACK BY TAU 72. THE COMBINATION
    OF STEADILY INCREASING VWS AND DECREASING SSTS WILL OFFSET THE
    CONTINUED ROBUST OUTFLOW, LEADING TO STEADY WEAKENING THROUGH TAU
    96. AROUND TAU 72, AS THE SYSTEM MOVES OVER WATERS COOLER THAN 26C
    AND BEGINS TO INTERACT WITH AN UPPER-LEVEL 200MB LOW, IT IS FORECAST
    TO TRANSITION TO A SUBTROPICAL STORM, COMPLETING THE TRANSITION BY
    TAU 96. NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 48
    AND THIS PORTION OF THE JTWC FORECAST IS LAID NEAR THE MULTI-MODEL
    CONSENSUS WITH HIGH CONFIDENCE. IN THE TAU 72-120 RANGE HOWEVER,
    THERE IS HIGH UNCERTAINTY IN THE TIMING AND STRENGTH OF THE TURN TO
    THE SOUTHWEST, WITH GFS BEING THE SHARPEST AND FASTEST TURN, WHILE
    THE ECMWF IS THE SLOWEST AND TURNS THE SYSTEM TOWARDS THE EAST,
    LEADING TO A NEARLY 600NM SPREAD BY TAU 120. THIS PORTION OF THE
    JTWC FORECAST TRACK LIES FAIRLY CLOSE THE GFS SOLUTION, TO THE WEST
    AND SLIGHTLY SLOWER THAN THE CONSENSUS TRACK WITH LOW CONFIDENCE DUE
    TO THE HIGH UNCERTAINTY IN THE TRACK GUIDANCE.MAXIMUM SIGNIFICANT
    WAVE HEIGHT AT 171200Z IS 30 FEET. NEXT WARNINGS AT 172100Z,
    180300Z, 180900Z AND 181500Z.//
    NNNN
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