WTXS31 PGTW 270900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/TROPICAL CYCLONE 07S (CHALANE) WARNING NR 006// RMKS/ 1. TROPICAL CYCLONE 07S (CHALANE) WARNING NR 006 01 ACTIVE TROPICAL CYCLONE IN SOUTHIO MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE WIND RADII VALID OVER OPEN WATER ONLY --- WARNING POSITION: 270600Z --- NEAR 18.1S 47.6E MOVEMENT PAST SIX HOURS - 260 DEGREES AT 11 KTS POSITION ACCURATE TO WITHIN 060 NM POSITION BASED ON CENTER LOCATED BY A COMBINATION OF SATELLITE AND SYNOPTIC DATA PRESENT WIND DISTRIBUTION: MAX SUSTAINED WINDS - 025 KT, GUSTS 035 KT WIND RADII VALID OVER OPEN WATER ONLY REPEAT POSIT: 18.1S 47.6E --- FORECASTS: 12 HRS, VALID AT: 271800Z --- 18.9S 45.5E MAX SUSTAINED WINDS - 025 KT, GUSTS 035 KT WIND RADII VALID OVER OPEN WATER ONLY VECTOR TO 24 HR POSIT: 245 DEG/ 09 KTS --- 24 HRS, VALID AT: 280600Z --- 19.7S 43.8E MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT WIND RADII VALID OVER OPEN WATER ONLY VECTOR TO 36 HR POSIT: 255 DEG/ 08 KTS --- 36 HRS, VALID AT: 281800Z --- 20.1S 42.2E MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT WIND RADII VALID OVER OPEN WATER ONLY RADIUS OF 034 KT WINDS - 025 NM NORTHEAST QUADRANT 045 NM SOUTHEAST QUADRANT 035 NM SOUTHWEST QUADRANT 000 NM NORTHWEST QUADRANT VECTOR TO 48 HR POSIT: 270 DEG/ 08 KTS --- EXTENDED OUTLOOK: 48 HRS, VALID AT: 290600Z --- 20.1S 40.5E MAX SUSTAINED WINDS - 040 KT, GUSTS 050 KT WIND RADII VALID OVER OPEN WATER ONLY RADIUS OF 034 KT WINDS - 035 NM NORTHEAST QUADRANT 045 NM SOUTHEAST QUADRANT 040 NM SOUTHWEST QUADRANT 035 NM NORTHWEST QUADRANT VECTOR TO 72 HR POSIT: 270 DEG/ 12 KTS --- 72 HRS, VALID AT: 300600Z --- 20.0S 35.4E MAX SUSTAINED WINDS - 050 KT, GUSTS 065 KT WIND RADII VALID OVER OPEN WATER ONLY RADIUS OF 050 KT WINDS - 000 NM NORTHEAST QUADRANT 030 NM SOUTHEAST QUADRANT 030 NM SOUTHWEST QUADRANT 000 NM NORTHWEST QUADRANT RADIUS OF 034 KT WINDS - 050 NM NORTHEAST QUADRANT 070 NM SOUTHEAST QUADRANT 070 NM SOUTHWEST QUADRANT 050 NM NORTHWEST QUADRANT VECTOR TO 96 HR POSIT: 265 DEG/ 13 KTS --- LONG RANGE OUTLOOK: --- 96 HRS, VALID AT: 310600Z --- 20.2S 29.8E MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT WIND RADII VALID OVER OPEN WATER ONLY DISSIPATING AS A SIGNIFICANT TROPICAL CYCLONE OVER LAND VECTOR TO 120 HR POSIT: 265 DEG/ 12 KTS --- 120 HRS, VALID AT: 010600Z --- 20.5S 24.5E MAX SUSTAINED WINDS - 025 KT, GUSTS 035 KT WIND RADII VALID OVER OPEN WATER ONLY DISSIPATED AS A SIGNIFICANT TROPICAL CYCLONE OVER LAND --- REMARKS: 270900Z POSITION NEAR 18.3S 47.1E. 27DEC20. TROPICAL CYCLONE 07S (CHALANE), LOCATED APPROXIMATELY 48 NM NORTH OF ANTANANARIVO, MADAGASCAR, HAS TRACKED WESTWARD AT 11 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THAT WHILE TC 07S IS OVER CENTRAL MADAGASCAR, IT HAS HELD TOGETHER SURPRISINGLY WELL, WITH WELL DEFINED SPIRAL BANDS WRAPPING INTO A WELL DEFINED LOW LEVEL CIRCULATION CENTER (LLCC). HOWEVER, CONVECTION HAS WANED AND THE MAJORITY OF THE SYSTEM IS NOW COMPRISED OF LOW TO MID-LEVEL CLOUDS. THE INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE BASED ON ANALYSIS OF THE SPIRAL BANDS, WITH SUPPORT FROM A 270543Z AMSU-B 89GHZ MICROWAVE IMAGE, WHICH ALSO CONFIRMS THE OVERALL LOW TO MID-LEVEL NATURE OF THE CIRCULATION. THE INITIAL INTENSITY IS ASSESSED AT 25 KNOTS WITH LOW CONFIDENCE, AND DUE TO THE LACK OF ANY SATELLITE-BASED INTENSITY ESTIMATES, IS BASED PRIMARILY ON THE OVERALL STRUCTURE OF THE SYSTEM AND GENERAL OVERLAND WEAKENING. ENVIRONMENTAL ANALYSIS INDICATES THAT, WITH THE EXCEPTION OF THE SYSTEM BEING OVERLAND, IT LIES WITHIN A FAVORABLE ENVIRONMENT OF LOW (5-10 KTS) VWS AND EASTERLY DIFFLUENT OUTFLOW DUE TO AN UPPER-LEVEL ANTICYCLONE OVER SOUTHERN MADAGASCAR. THE SYSTEM IS TRACKING SOUTHWESTWARD ALONG THE NORTHWESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) POSITIONED TO THE SOUTHEAST. TC 07S IS FORECAST TO CONTINUE TRACKING SOUTHWESTWARD OVER THE NEXT 24 HOURS, EMERGING BACK OVER WATER IN THE EASTERN MOZAMBIQUE CHANNEL BY TAU 24. BY TAU 36, A NEW STR LOCATED TO THE SOUTH OF THE MOZAMBIQUE CHANNEL WILL ASSUME THE DOMINANT STEERING ROLE, DRIVING THE SYSTEM ONTO A WESTWARD TRACK THROUGH THE REMAINDER OF THE FORECAST PERIOD. TC 07S IS EXPECTED TO MAKE LANDFALL NEAR BEIRA, MOZAMBIQUE JUST AFTER TAU 72. ENVIRONMENTAL CONDITIONS ARE EXPECTED TO BE EXCELLENT WITHIN THE CHANNEL, WITH VERY WARM (30-31 CELSIUS) SSTS, HIGH OHC, LOW VWS AND STRONG EQUATORWARD OUTFLOW, WHICH WILL SUPPORT INTENSIFICATION FROM TAU 24 TO TAU 72, REACHING A PEAK OF 50 KNOTS JUST PRIOR TO LANDFALL. AFTER LANDFALL, THE SYSTEM IS FORECAST TO STEADILY WEAKEN DUE TO LAND INTERACTION, DISSIPATING NO LATER THAN TAU 120. NUMERICAL MODEL GUIDANCE IS IN GENERALLY GOOD AGREEMENT ON THE TRACK, WITH ONLY 75NM SPREAD AT TAU 36, INCREASING TO 140NM AT TAU 72. HOWEVER, UNCERTAINTY IN THE AMOUNT OF TERRAIN INTERACTION OVER MADAGASCAR, AND THE INFLUENCE THIS WILL HAVE ON THE ULTIMATE TRACK AND INTENSITY, MEAN THAT THE OVERALL FORECAST HAS A HIGH DEGREE OF UNCERTAINTY, LENDING LOW CONFIDENCE TO THE JTWC FORECAST. NEXT WARNINGS AT 272100Z AND 280900Z.// NNNN