Update: Cyclone Season 2012: Tropical Cyclone Giovanna (Southern Indian Ocean) 19 February 2012 19h00 SAST

Giovanna has once again changed direction and also increased in intensity. Giovanna is now a Cat. 2 storm. Like I indicated before, Giovanna is one of the weirdest storms I have observed in the South Indian Ocean. What will happen in the next 12 hours. Your guess is as good as mine. Here is the latest prediction by the JTWC. - SAWDOS

191500Z POSITION NEAR 26.0S 51.0E.
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 MULTISPECTRAL SATELLITE IMAGERY SHOWS THAT TC 12S UNDERWENT ANOTHER PERIOD OF INTENSIFICATION OVER THE PAST 12 HOURS, INCLUDING A GROWTH IN HORIZONTAL EXTENT AND THE FORMATION OF A WELL-DEFINED EYE, WHICH HAS RECENTLY COLLAPSED. THE CURRENT POSITION IS EXTRAPOLATED FROM A 190757 TRMM 85GHZ MICROWAVE SATELLITE IMAGE AND IS IN AGREEMENT WITH PGTW AND KNES FIXES. THE CURRENT INTENSITY IS ASSESSED AT 85 KNOTS, WHICH IS AN AVERAGE OF AGENCY FIXES RANGING FROM 77 TO 90 KNOTS. UPPER LEVEL ANALYSIS INDICATES THE SYSTEM IS NOW POLEWARD OF THE
SUBTROPICAL RIDGE AXIS AND BEGINNING TO FEEL THE EFFECTS OF STRONG VERTICAL WIND SHEAR (VWS) ASSOCIATED WITH THE MID-LATITUDE WESTERLY FLOW. ANIMATED WATER VAPOR IMAGERY CLEARLY DEPICTS TC 12S BEING STRETCHED TO THE SOUTHEAST IN RESPONSE TO A DEEP TROUGH APPROACHING
FROM THE WEST, WHICH IS ADDING TO THE VWS. THE SYSTEM HAD BEEN TRACKING ALONG THE SOUTHERN PERIPHERY OF AN ANTICYCLONE TO THE WEST, AND THE PREVIOUS FORECAST HAD CALLED FOR A NORTHWARD TURN IN THE MID- RANGE TAUS. HOWEVER, THIS FORECAST, WHICH TRACKS THE SYSTEM EASTWARD AND THEN TURNS INTO THE WESTERLIES, MARKS A CHANGE IN THE PREVAILING PHILOSOPHY. TC 12S HAS MOVED RAPIDLY EASTWARD, AND THE APPROACHING UPPER-LEVEL TROUGH SHOULD FORCE THE STORM IN A EAST-SOUTHEASTWARD DIRECTION, AFTER WHICH AN ANTICYCLONE TO THE EAST WILL BECOME THE DOMINANT STEERING MECHANISM. AS TC 12S TRACKS MORE POLEWARD, VWS WILL CONTINUE TO INCREASE AND HASTEN THE DISSIPATION. IN LIEU OF THIS FORECAST CHANGE, THE SYSTEM IS NOW EXPECTED TO BEGIN EXTRA- TROPICAL TRANSITION (ETT) AT TAU 48, AND SHOULD COMPLETE ETT BY TAU 72, BY WHICH TIME IT WILL BE FULLY EMBEDDED WITHIN THE BAROCLINIC ZONE. THERE IS SIGNIFICANT DISAGREEMENT AMONG THE NUMERICAL MODEL GUIDANCE REGARDING THE FORECAST TRACK. THE ECMWF MODEL STILL CALLS FOR A NORTHWARD TURN, BUT A REVIEW OF LIMITED MODEL FIELDS INDICATES THE MODEL ACTUALLY DISSIPATES THE SYSTEM BY TAU 48 AND BEGINS TRACKING ANOTHER CIRCULATION. THE GFDN AND NOGAPS MODELS INDICATE N INITIAL BEND EQUATORWARD FOLLOWED BY A RECURVATURE. FINALLY, GFS AND WBAR GENERALLY AGREE ON AN EAST-SOUTHEAST TRACK AND ETT. THE FORECAST TRACK IS BIASED TOWARDS THE GFS SOLUTION. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 191200Z IS 20 FEET.

- CIMSS and JTWC