Update: Cyclone Season 2012: Tropical Cyclone Giovanna (Southern Indian Ocean) 12 February 2012 20h00 SAST

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121500Z POSITION NEAR 17.7S 56.0E.
TROPICAL CYCLONE (TC) 12S (GIOVANNA), LOCATED APPROXIMATELY 200 NM NORTH-NORTHEAST OF LA REUNION, HAD TRACKED WESTWARD AT 10 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS THAT TC 12S IS STRUGGLING TO MAINTAIN A CLOUD-FREE EYE. A 121108Z AMSU-B IMAGE INDICATES AN APPROXIMATELY 35 NM WIDE EYE. COMPARISON OF THIS AMSU-B IMAGE TO AMSU-B IMAGES IN THE PAST 6-12 HOURS REVEALS A WEAKENING IN THE DEEP CENTRAL CONVECTION SURROUNDING THE LOW-LEVEL CIRCULATION CENTER (LLCC). THE CURRENT POSITION IS BASED ON AGREEABLE PGTW, KNES, FMEE, AND FIMP CENTER FIXES ALONG WITH THE AMSU-B IMAGE WITH HIGH CONFIDENCE. THE CURRENT INTENSITY IS BASED ON DVORAK ESTIMATES OF 90-102 KNOTS FROM THESE REPORTING AGENCIES. UPPER-LEVEL ANALYSIS CONTINUES TO SHOW A SELF-INDUCED MESO-ANTICYCLONE OVER THE LLCC WHICH IS PRODUCING EXCELLENT DIVERGENCE ALOFT AND WEAK VERTICAL WIND SHEAR (VWS). ANIMATED WATER VAPOR IMAGERY ALSO CONTINUES TO SHOW EXCELLENT RADIAL OUTFLOW. TC GIOVANNA'S TRACK SPEED HAD ACCELERATED OVER THE PAST SIX HOURS AS A DEEP-LAYERED SUBTROPICAL RIDGE (STR) BUILDS IN FROM THE SOUTH. THE SYSTEM WILL TRACK WESTWARDS ALONG THE NORTHERN PERIPHERY OF THIS STR DURING THE NEXT TWO DAYS. DURING THIS TIME TC 12S SHOULD SLIGHTLY INTENSIFY AS IT MAKES LANDFALL OVER CENTRAL MADAGASCAR JUST AFTER TAU 36. DURING TAU 48 THE LLCC WILL WEAKEN SIGNIFICANTLY DUE TO THE FRICTIONAL FORCES OF TOPOGRAPHIC INTERACTION. BY TAU 72 THE SYSTEM SHOULD EMERGE OVER THE WARM WATERS OF THE MOZAMBIQUE CHANNEL AND TRACK SOUTHWESTWARDS ALONG THE WESTERN PERIPHERY OF THE STR. BY TAU 96, THE LLCC MAY HEAD TOWARDS A SLIGHT COL REGION IN BETWEEN THE STR TO THE EAST AND A BUILDING RIDGE OVER SOUTHERN AFRICA. BY TAU 120 THE NEW STEERING INFLUENCE OF THE STR OVER SOUTHERN AFRICA MAY DEFLECT TC 12S ON A MORE WEST-NORTHWESTWARDS TRACK INTO SOUTHERN MOZAMBIQUE WHERE THE SYSTEM WILL BEGIN TO DISSIPATE OVERLAND. DURING ITS TRANSIT OVER THE MOZAMBIQUE CHANNEL THE SYSTEM SHOULD ONLY SLIGHTLY RE-INTENSIFY DUE TO THE UNFAVORABLE INFLUENCES OF VWS AND LIMITED TIME OVER WATER. NUMERICAL MODEL GUIDANCE IS IN TIGHT AGREEMENT UNTIL THE LLCC TRACKS OVER MADAGASCAR AND EMERGES OVER THE CHANNEL AND IS SPLIT INTO TWO MAIN GROUPINGS. THE ECMWF, NOGAPS, AND GFS LIE RIGHT OF CONSENSUS AND THE GFDN AND EGRR LIE TO THE LEFT. THIS FORECAST FAVORS THE FIRST GROUPING TO THE RIGHT OF CONSENSUS BASED ON MORE MEMBERS AND PAST MODEL PERFORMANCE. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 121200Z IS 26 FEET.

- Joint Typhoon Warning Center (JTWC)