Tropical Cyclone Activity: Indian Ocean

Tropical Cyclone Formation (East of Madagascar) Alert WTXS21 Issued at 31/0000Z

WTXS21 PGTW 310000
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE FORMATION ALERT//
REF/A/JOINT TYPHOON WRNCEN PEARL HARBOR HI/292351Z DEC 12//
AMPN/REF IS TROPICAL CYCLONE FORMATION ALERT (WTXS21 PGTW 300000)//
RMKS/
1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN
150 NM EITHER SIDE OF A LINE FROM 10.3S 59.5E TO 12.9S 55.8E WITHIN
THE NEXT 06 TO 24 HOURS. AVAILABLE DATA DOES NOT JUSTIFY ISSUANCE OF
NUMBERED TROPICAL CYCLONE WARNINGS AT THIS TIME. WINDS IN THE AREA
ARE ESTIMATED TO BE 25 TO 30 KNOTS. METSAT IMAGERY AT 302330Z
INDICATES THAT A CIRCULATION CENTER IS LOCATED NEAR 10.5S 58.7E. 
THE SYSTEM IS MOVING WESTWARD AT 08 KNOTS.
2. REMARKS: THE AREA OF CONVECTION PREVIOUSLY LOCATED NEAR 10.5S
59.6E IS NOW LOCATED NEAR 10.5S 58.7E, APPROXIMATELY 665 NM NORTH-
NORTHEAST OF LA REUNION. ANIMATED INFRARED SATELLITE IMAGERY
DEPICTS A PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC)
POSITIONED ALONG THE NORTHEASTERN EDGE OF A LARGE, PERSISTENT AREA
OF DEEP CONVECTION. A 302144Z AMSU IMAGE DEPICTS A BROAD LLCC WITH A
CURVED CONVECTIVE BAND OVER THE WESTERN SEMI-CIRCLE AND DEFINED
SHALLOW BANDING ELSEWHERE. A 301715Z ASCAT IMAGE ALSO SHOWED AN
ELONGATED CIRCULATION WITH AN EXTENSIVE AREA OF 25 TO 30 KNOT WINDS
OVER THE NORTHERN SEMI-CIRCLE. THE DISTURBANCE IS LOCATED
EQUATORWARD OF THE UPPER-LEVEL SUBTROPICAL RIDGE AXIS AND IS UNDER
MODERATE TO STRONG, EASTERLY VERTICAL WIND SHEAR (VWS), WHICH HAS
DECREASED OVER THE PAST 24 HOURS. DYNAMIC MODELS CONTINUE TO
AGGRESSIVELY DEVELOP THE SYSTEM AS VWS IS EXPECTED TO DECREASE OVER
THE 12 TO 24 HOURS. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT
25 TO 30 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR
1000 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL
CYCLONE WITHIN THE NEXT 24 HOURS IS HIGH. THIS SUPERSEDES REF A.
3. THIS ALERT WILL BE REISSUED, UPGRADED TO WARNING OR CANCELLED BY
010000Z.//
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ABIO10 PGTW 310300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/SIGNIFICANT TROPICAL WEATHER ADVISORY FOR THE INDIAN
/OCEAN REISSUED/310300Z-311800ZDEC2012//
REF/A/MSG/JOINT TYPHOON WRNCEN PEARL HARBOR HI/302351ZDEC2012//
AMPN/REF A IS A TROPICAL CYCLONE FORMATION ALERT.//
RMKS/
1. NORTH INDIAN OCEAN AREA (MALAY PENINSULA WEST TO COAST OF AFRICA):
A. TROPICAL CYCLONE SUMMARY: NONE.
B. TROPICAL DISTURBANCE SUMMARY: NONE.
2. SOUTH INDIAN OCEAN AREA (135E WEST TO COAST OF AFRICA):
A. TROPICAL CYCLONE SUMMARY: NONE.
B. TROPICAL DISTURBANCE SUMMARY:
(1) THE AREA OF CONVECTION PREVIOUSLY LOCATED NEAR 10.5S
59.6E IS NOW LOCATED NEAR 10.5S 58.7E, APPROXIMATELY 665 NM NORTH-
NORTHEAST OF LA REUNION. ANIMATED INFRARED SATELLITE IMAGERY
DEPICTS A PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC)
POSITIONED ALONG THE NORTHEASTERN EDGE OF A LARGE, PERSISTENT AREA
OF DEEP CONVECTION. A 302144Z AMSU IMAGE DEPICTS A BROAD LLCC WITH A
CURVED CONVECTIVE BAND OVER THE WESTERN SEMI-CIRCLE AND DEFINED
SHALLOW BANDING ELSEWHERE. A 301715Z ASCAT IMAGE ALSO SHOWED AN
ELONGATED CIRCULATION WITH AN EXTENSIVE AREA OF 25 TO 30 KNOT WINDS
OVER THE NORTHERN SEMI-CIRCLE. THE DISTURBANCE IS LOCATED
EQUATORWARD OF THE UPPER-LEVEL SUBTROPICAL RIDGE AXIS AND IS UNDER
MODERATE TO STRONG, EASTERLY VERTICAL WIND SHEAR (VWS), WHICH HAS
DECREASED OVER THE PAST 24 HOURS. DYNAMIC MODELS CONTINUE TO
AGGRESSIVELY DEVELOP THE SYSTEM AS VWS IS EXPECTED TO DECREASE OVER
THE 12 TO 24 HOURS. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT
25 TO 30 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR
1000 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL
CYCLONE WITHIN THE NEXT 24 HOURS REMAINS HIGH. SEE REF A (WTXS21
PGTW 310000) FOR FURTHER DETAILS.
(2) THE AREA OF CONVECTION PREVIOUSLY LOCATED NEAR 9.4S 85.2E
IS NOW LOCATED NEAR 9.3S 85.8E, APPROXIMATELY 790 NM EAST OF DIEGO
GARCIA. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS AN EXPOSED
LOW-LEVEL CIRCULATION CENTER (LLCC) WITH FLARING DEEP CONVECTION
OVER THE WEST QUADRANT. A 301534Z METOP-A IMAGE INDICATES AN
IMPROVING, DEFINED LLCC WITH CONVECTIVE BANDING WRAPPING INTO THE
BROAD CENTER. A 301534Z ASCAT IMAGE DEPICTS AN ELONGATED CIRCULATION
WITH 20 TO 25 KNOT WINDS. OVER THE PAST 24 HOURS, THE UPPER-LEVEL
ENVIRONMENT HAS IMPROVED SLIGHTLY WITH A WEAK ANTICYCLONE POSITIONED
NEAR THE LLCC AND IMPROVED POLEWARD OUTFLOW INTO A DEEP SHORTWAVE
TROUGH TO THE SOUTH. HOWEVER, VERTICAL WIND SHEAR HAS REMAINED
MODERATE TO STRONG (20 TO 30 KNOTS). MAXIMUM SUSTAINED SURFACE WINDS
ARE ESTIMATED AT 20 TO 25 KNOTS. MINIMUM SEA LEVEL PRESSURE IS
ESTIMATED TO BE NEAR 1004 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A
SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS REMAINS MEDIUM.
(3) NO OTHER SUSPECT AREAS./
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- JTWC