Tropical Storm Activity: South Indian Ocean (16 January 2013)

Tropical Cyclone 09S (Emang) Issued at 16/0900Z

160900Z POSITION NEAR 14.3S 77.3E.
TROPICAL CYCLONE (TC) 09S (EMANG), LOCATED APPROXIMATELY 515 NM
SOUTHEAST OF DIEGO GARCIA, HAS TRACKED WESTWARD AT 03 KNOTS OVER THE
PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY SHOWS
RECENT FLARING DEEP CONVECTION NEAR THE LOW LEVEL CIRCULATION CENTER
(LLCC), HOWEVER OVERALL IMPROVEMENTS IN THE STRUCTURE HAVE BEEN SLOW
TO DEVELOP. AN OLDER 151855Z OSCAT PASS SHOWED A WELL DEFINED LLCC,
WITH WEAKER WINDS IN THE NORTHERN HALF OF THE SYSTEM AND A BROADER
SWATH OF 30 TO 35 KNOT WINDS IN THE SOUTHERN QUADRANTS. UPPER LEVEL
ANALYSIS INDICATES TC 09S REMAINS NEAR THE AXIS OF A SUBTROPICAL
RIDGE (STR). THIS ENVIRONMENT IS SUPPORTING LOW TO MODERATE LEVELS OF
VERTICAL WIND SHEAR (VWS) (10 TO 15 KNOTS). THE SYSTEM IS LOCATED IN
A REGION OF MODERATELY FAVORABLE SEA SURFACE TEMPERATURES (SSTS) (27
TO 28 CELSIUS). TC 09S IS TRACKING MORE WESTWARD AS A LOW- TO MID-
LEVEL STR BUILDS BACK TO THE SOUTH OF THE SYSTEM IN RESPONSE TO A
TRANSITORY DEEP-LAYERED TROUGH MOVING FURTHER TO THE SOUTHEAST, AWAY
FROM THE STR. MODEL GUIDANCE INDICATES TC 09S WILL REMAIN ON A
GENERALLY WEST-SOUTHWESTWARD TRACK AROUND THE STR. A BRIEF PERIOD OF
IMPROVING UPPER LEVEL ENVIRONMENT WILL ALLOW FOR SLOW INTENSIFICATION
OVER THE NEXT 48 HOURS, BUT INCREASING VWS BEYOND TAU 72 WILL CAUSE
WEAKENING OF THE SYSTEM THROUGH THE END OF THE FORECAST PERIOD.
NUMERICAL MODEL GUIDANCE IS LIMITED BUT IN FAIR AGREEMENT LENDING
HIGH CONFIDENCE TO THE TRACK FORECAST. MAXIMUM SIGNIFICANT WAVE
HEIGHT AT 160600Z IS 15 FEET.

- JTWC + EUMETSAT