Update: Cyclone Season 2012: Tropical Cyclone Giovanna (Southern Indian Ocean) 20 February 2012 11h00 SAST

200300Z POSITION NEAR 26.4S 53.7E.
TROPICAL CYCLONE 12S (GIOVANNA), LOCATED APPROXIMATELY 455 NM SOUTH-SOUTHEAST OF ANTANANARIVO, MADAGASCAR, HAS TRACKED EASTWARD AT 14 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED (IR) SATELLITE IMAGERY SHOWS THE ORGANIZATION OF THE BANDING CONVECTION OVER THE LOW LEVEL CIRCULATION CENTER (LLCC) HAS STARTED TO BREAK DOWN AS TC 12S HAS MOVED SOUTH OF AN UPPER LEVEL SUBTROPICAL RIDGE (STR) AXIS INTO HIGH VERTICAL WIND SHEAR (VWS) (30 KNOTS PLUS). THE EQUATORWARD OUTFLOW CHANNEL HAS BEEN RAPIDLY WEAKENING, HOWEVER THE POLEWARD OUTFLOW CHANNEL REMAINS VERY FAVORABLE WITH SUPPORT FROM A DEEP MID-LATITUDE TROUGH AMPLIFYING THE WESTERLY OUTFLOW GRADIENT. THE CURRENT POSITION IS BASED ON LOOPING IR IMAGERY AND FIXES FROM PGTW AND KNES, BUT AS CENTRAL CONVECTION HAS LOST ORGANIZATION, THERE IS ONLY MARGINAL CONFIDENCE IN THE POSITION. THE CURRENT INTENSITY IS BASED ON DVORAK ESTIMATES FROM PGTW AND KNES INDICATING 65 KNOTS. TC 12S IS CURRENTLY TRACKING ALONG THE LEADING EDGE OF A DEEP MID-LATITUDE TROUGH AND THE SOUTHWESTERN PERIPHERY OF A DEEP STR BUILDING TOWARDS MADAGASCAR. TC 12S IS EXPECTED TO CONTINUE TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF THE STR THROUGH TAU 48. INTENSITIES WILL RAPIDLY DECREASE AS THE MID-LATITUDE TROUGH TRACKS EASTWARD LEADING TO INCREASED VWS. ADDITIONALLY, TC 12S WILL TRACK OVER DECREASING SEA SURFACE TEMPERATURES, WEAKENING THE LLCC. THE SYSTEM IS EXPECTED TO START EXTRA-TROPICAL TRANSITION BY TAU 36 AND SHOULD BE COMPLETE BY TAU 48. MODEL GUIDANCE IS IN FAIR AGREEMENT WITH THE SOUTHEASTERN TRACK, HOWEVER THE MAJORITY SLOW THE SYSTEM
BETWEEN TAU 12 AND 36. THIS IS LIKELY DUE TO MODELS SHOWING TC 13S AS A MORE INTENSE SYSTEM THAN CURRENTLY FORECAST, WHICH LEADS TO A WEAKER STEERING RIDGE ALONG THE STRS WESTERN PERIPHERY. BASED ON THE CURRENT INTENSITIES FOR TC 13S BEING LESS THAN MODEL GUIDANCE SUGGESTS, THE TRACK SPEED FOR TC 12S HAS BEEN KEPT HIGHER THAN CONSENSUS INDICATES. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 200000Z IS 20 FEET.

- JTWC