Image: NOAA18 01H08 SAST (Nic Cronje, Nelspruit) Click on image for larger view.
180300Z POSITION NEAR 26.4S 43.5E.
TROPICAL CYCLONE 12S (GIOVANNA), LOCATED APPROXIMATELY 495 NM SOUTH-SOUTHWEST OF ANTANANARIVO, MADAGASCAR, HAS TRACKED SOUTHEASTWARD AT 03 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY SHOWS A WELL DEFINED LOW LEVEL CIRCULATION CENTER (LLCC)WITH GOOD POLEWARD OUTFLOW SUPPORTING THE CURRENT 55 KNOT INTENSITY. OVER THE PAST 12 HOURS, TC 12S HAD SEEN A BRIEF PERIOD OF WEAKENING, HOWEVER IN THE LAST SIX HOURS IMPROVING LOW LEVEL INFLOW AND ENHANCED POLEWARD OUTFLOW HAS LED TO A BRIEF INTENSIFICATION OF THE LLCC. TC 12S HAS BEEN TRACKING SLOWLY OVER THE PAST 12 HOURS AS THE COMPETING STEERING INFLUENCES FROM THE SUBTROPICAL RIDGE (STR) LOCATED OVER SOUTHERN AFRICA AND THE STR LOCATED OVER MADAGASCAR HAVE REMAINED EQUALLY INFLUENTIAL. UPPER LEVEL ANALYSIS SHOWS THE STRONG POLEWARD OUTFLOW PRESENT OVER THE PAST 48 HOURS IS BEGINNING TO BE IMPINGED BY A WESTERLY JET OUT OF SOUTH AFRICA, AND WILL FURTHER WEAKEN THE SYSTEM AS VERTICAL WIND SHEAR (VWS) INCREASES. TC 12S IS EXPECTED TO MAINTAIN A GENERALLY EASTWARD TRACK AS BOTH STRS INTERACT, WITH THE STR OVER MADAGASCAR BEING SLIGHTLY MORE DOMINANT. INTENSITY WILL DECREASE BASED ON MARGINAL LOW LEVEL SUPPORT AND INCREASING VWS HAMPERING UPPER LEVEL OUTFLOW. MODEL AND INTENSITY GUIDANCE ARE IN FAIR AGREEMENT WITH THIS FORECAST. THE OUTLIERS ARE NGPS AND WBAR SHOWING TC 12S TRACKING INTO THE MID-LATITUDE FLOW VICE A RECURVATURE TO THE NORTH AS DEPICTED BY EGRR, GFS, AND ECMF. THIS FORECAST DISSIPATES TC 12S BY TAU 48, AND FAVORS THE GFS AND ECMF SOLUTION. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 180000Z IS 15 FEET.
- Joint Typhoon Warning Center (JTWC)
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