Update: Cyclone Season 2012: Tropical Cyclone Giovanna (Southern Indian Ocean) 15 February 2012 21H00 SAST

151500Z POSITION NEAR 23.7S 41.3E.
TROPICAL CYCLONE (TC) 12S (GIOVANNA), LOCATED APPROXIMATELY 405 NM SOUTHWEST OF ANTANANARIVO, MADAGASCAR, HAS TRACKED SOUTHWESTWARD AT 12 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) REVEALS THE LOW LEVEL CIRCULATION CENTER (LLCC) BECAME DISPLACED FROM THE DEEP CONVECTION WHILE CROSSING MADAGASCAR DUE TO THE LEE-SIDE JUMP PHENOMENON. THE LLCC IS NOW PARTIALLY EXPOSED, WITH THE DEEPEST CONVECTION BUILDING ALONG THE NORTHERN SEMICIRCLE. NOW THAT TC 12S IS TRACKING OVER THE OPEN WATER OF THE MOZAMBIQUE CHANNEL, THE TIGHTLY CURVED SPIRAL BANDING IS CONSOLIDATING AND THE SYSTEM IS REGENERATING. A 150626Z AMSU-B LOW LEVEL COLOR COMPOSITE SUPPORTS THIS ASSESSMENT. THE CURRENT POSITION IS BASED ON THE EXPOSED LLCC IN THE MSI WITH EXCELLENT CONFIDENCE. UPPER LEVEL ANALYSIS INDICATES TC 12S IS NOW APPROXIMATELY TWO DEGREES EQUATORWARD OF THE SUBTROPICAL RIDGE (STR) AXIS, WITH FAVORABLY LOW VERTICAL WIND SHEAR (VWS), WHICH SHOULD PERSIST FOR THE NEXT SEVERAL DAYS. ADDITIONALLY, TC 12S IS BENEFITTING FROM VIGOROUS EQUATORWARD UTFLOW OVER THE AFRICAN CONTINENT AS WELL AS AN IMPROVING POLEWARD CHANNEL. SEA SURFACE TEMPERATURES ARE A FAVORABLE 29-30 DEGREES CELSIUS. GIVEN THE ENVIRONMENTAL CONDITIONS, THE INTENSITY IS EXPECTED TO STEADILY INCREASE OVER THE NEXT 72 HOURS TO A PEAK OF 65 KNOTS, AFTER WHICH VWS VALUES SHOULD CAUSE THE SYSTEM TO SLOWLY WEAKEN. TC 12S IS CURRENTLY TRACKING ALONG THE WESTERN PERIPHERY OF A DEEP LAYER STR LOCATED TO THE EAST. THERE IS CONSIDERABLE DISAGREEMENT IN THE NUMERICAL MODEL GUIDANCE, WITH NO CLEAR GROUPINGS. THIS MAY BE DUE IN PART TO THE LEE-SIDE JUMP AND POOR PLACEMENT OF THE LLCC WITHIN THE MODEL INITIALIZATIONS. THE OTHER FACTOR IS THE DEPTH AT WHICH TC 12S WILL BE STEERED. THE MODELS WHICH BUILD THE SYSTEM TO 60-65 KNOTS FOLLOW THE DEEP LAYER STEERING, WHICH WOULD CONTINUE THE SOUTHWESTWARD MOTION ALONG A WEAKNESS IN THE STR, UNTIL FINALLY TURNING THE SYSTEM BACK TO THE SOUTHEAST AROUND TAU 96. MODELS THAT INDICATE WEAK DEVELOPMENT ARE TRACKING MORE WESTWARD OR EVEN EQUATORWARD. GIVEN THE FAVORABLE ENVIRONMENTAL CONDITIONS NOTED AND THE PERSISTENCE OF THE ECMWF MODEL OVER SEVERAL DAYS TO INDICATE A SOUTHEASTWARD TURN, THE FORECAST IS BIASED TOWARDS THAT SOLUTION VERSUS THE CONSENSUS, WHICH INDICATES EQUATORWARD MOTION. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 151200Z IS 15 FEET.

- Joint Typhoon Warning Center (JTWC) + CIMSS Tropical Cyclones