Current Southern Hemisphere Tropical Systems: Tropical Cyclone 13S Felleng

310900Z POSITION NEAR 18.6S 51.1E.
TROPICAL CYCLONE (TC) 13S (FELLENG), LOCATED APPROXIMATELY 300 NM WEST-NORTHWEST OF LA REUNION, HAS TRACKED SOUTHWESTWARD AT 06 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI)INDICATES THAT TC 13S HAS CONTINUED TO WEAKEN OVER THE PAST SIX HOURS AS DEEP CONVECTION HAS CONTINUED TO DECREASE, LOSING ITS EYE
IN THE MSI AND INFRARED IMAGERY. A RECENT 310444Z SSMIS 37GHZ MICROWAVE IMAGE DEPICTS A MICROWAVE EYE FEATURE WITH THE DEEP CONVECTION CONFINED TO THE EASTERN SEMI-CIRCLE. THERE IS HIGH CONFIDENCE IN THE INITIAL POSITION BASED ON THE MICROWAVE IMAGE. THE
INITIAL INTENSITY IS ASSESSED AT 85 KNOTS WHICH IS SLIGHTLY LOWER THAN DVORAK CURRENT INTENSITY ESTIMATES OF 90 KNOTS FROM PGTW AND KNES, BASED ON THE OVERALL WEAKENING TREND. UPPER-LEVEL ANALYSIS REVEALS AMPLE EQUATORWARD AND POLEWARD OUTFLOW WHICH IS BEING OFFSET BY MODERATE VERTICAL WIND SHEAR (10-20 KNOTS). TC 13S IS CURRENTLY
TRACKING SOUTHWESTWARD BUT HAS SLOWED CONSIDERABLY OVER THE PAST SIX HOURS, TRACKING ALONG THE WESTERN PERIPHERY OF A SUBTROPICAL STEERING RIDGE (STR) SITUATED TO THE EAST. DESPITE THE CURRENT MOTION, TC 13S IS FORECAST TO TRACK SOUTH FOR THE NEXT 24 HOURS ALONG THE STR AND THEN MORE SOUTHEASTWARD AS IT ROUNDS THE STR AXIS AND ACCELERATES INTO THE MIDLATITUDE WESTERLIES. TC 13S WILL CONTINUE TO WEAKEN THROUGH THE FORECAST PERIOD AS VERTICAL WIND SHEAR WILL CONTINUE TO HAMPER THE SYSTEM AND COOLER SEA SURFACE TEMPERATURES (SSTS) ARE FORECAST PAST TAU 48. TC 13S WILL BEGIN
EXTRA TROPICAL TRANSITION (ETT) AT TAU 72 AS IT DRIVES INTO COLD (TWENTY SIX DEGREES CELCIUS) EMBEDDED INTO THE MIDLATITUDE WESTERLIES. DYNAMIC MODEL GUIDANCE IS IN TIGHT AGREEMENT THROUGH TAU 72 BUT DIVERGES IN THE EXTENDED TAUS DUE TO MINOR DIFFERENCES IN HOW EACH MODEL DEPICTS THE ORIENTATION AND STRENGTH OF THE STR. THE JTWC FORECAST IS POSITIONED CLOSE TO, BUT SLIGHTLY FASTER THAN, THE MULTI-MODEL CONSENSUS. THERE IS HIGH CONFIDENCE IN THE FORECAST TRACK. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 310600Z IS 32 FEET.

- JTWC + EUMETSAT