Tropical Cyclone 12S (Giovanna) Active Tropical Cyclone in South Indian Ocean

110300Z POSITION NEAR 16.9S 59.8E.
TROPICAL CYCLONE (TC) 12S (GIOVANNA), LOCATED APPROXIMATELY 365 NM NORTHEAST OF LA REUNION, HAS TRACKED SOUTHWESTWARD AT 11 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY SHOWS THE SYSTEM HAS MAINTAINED DEEP, HIGHLY-SYMMETRICAL AND VERY COMPACT CONVECTIVE BANDING AROUND A 15-NM DIAMETER EYE. RECENT WATER VAPOR SATELLITE ANIMATION DISPLAYS EXCELLENT RADIAL OUTFLOW WITH A VERY EFFICIENT POLEWARD CHANNEL. THE INITIAL POSITION IS PLACED OVER THE EYE FEATURE WITH HIGH CONFIDENCE AND THE INITIAL INTENSITY IS SUPPORTED BY DVORAK ESTIMATES FROM FMEE, PGTW AND KNES. UPPER LEVEL ANALYSIS INDICATES TC 12S IS IN A VERY FAVORABLE ENVIRONMENT OF LOW VERTICAL WIND SHEAR IN A DIFFLUENT ZONE UNDER A RIDGE AXIS. IT IS EXPECTED TO CONTINUE TRACKING ALONG THE NORTHWEST PERIPHERY OF A 
DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE SOUTHEAST. AFTER TAU 12, AN EXTENSION OF A SECONDARY STR CURRENTLY ANCHORED OVER MOZAMBIQUE CHANNEL WILL ASSUME STEERING. THE TRANSITION WILL CAUSE A SLIGHTLY MORE WESTWARD DIRECTION IN THE FORECAST TRACK. TC GIOVANNA WILL CONTINUE TO INTENSIFY OVER THE NEXT 48 HOURS PEAKING AT 135 KNOTS BEFORE MAKING LANDFALL IN MADAGASCAR AND EXITING INTO THE MOZAMBIQUE CHANNEL JUST BEFORE TAU 96. THE AVAILABLE NUMERICAL GUIDANCE IS IN 
VERY TIGHT AGREEMENT WITH THIS TRACK FORECAST WITH WBAR AS THE SOLE LEFT OUTLIER AFTER TAU 36. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 110000Z IS 26 FEET.

DUE TO THE FAVORABLE ENVIRONMENT, TC 12S (GIOVANNA) IS FORECAST TO STRENGHTHEN TO A PEAK OF 135 KNOTS. THE SYSTEM IS EXPECTED TO WEAKEN SIGNIFICANTLY AS IT TRACKS ACROSS MADAGASCAR; HOWEVER, RE-DEVELOPMENT IS EXPECTED IN THE MOZAMBIQUE CHANNEL AFTER TAU 120.

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