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.//
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