TC 20S(BILLY): has peaked just below Typhoon intensity//Remnants of TC 19S(GOMBE): Medium//Invest 91B and Invest 91S: Low,15/15utc

JTWC IS ISSUING 12HOURLY WARNINGS ON TC 20S(BILLY). 3HOURLY SATELLITE BULLETINS ARE ISSUED ON 20S, ON THE REMNANTS OF TC 19S(GOMBE), ON INVEST 91B AND INVEST 91S.

15/1010UTC.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TC 20S (BILLY) IS CURRENTLY TRACKING WESTWARD ON THE NORTHWESTERN PERIPHERY OF A WEAK EXTENSION OF THE SUBTROPICAL RIDGE (STR) AND IS EXPECTED TO TRACK GENERALLY WEST-SOUTHWESTWARD THROUGH 24H. PERSISTENT MODERATE TO HIGH VERTICAL WIND SHEAR COUPLED WITH INCREASING DRY AIR ENTRAINMENT, OFFSET SOMEWHAT BY MODERATE OUTFLOW, WILL STEADILY ERODE CENTRAL CONVECTION AND THE OVERALL STRUCTURE RESULTING IN STEADY WEAKENING. AFTER 24H, A BROAD MIDLATITUDE TROUGH WILL BREAK DOWN AND REORIENT THE STR PRODUCING A SOUTHWESTWARD TRACK THROUGH 48H. THE SYSTEM WILL CONTINUE TO WEAKEN DUE TO HIGH VERTICAL WIND SHEAR AND DRY AIR ENTRAINMENT. AFTER 48H, TC 20S WILL TURN WESTWARD UNDER THE LOW-LEVEL STR, WHICH IS EXPECTED TO BUILD IN TO THE SOUTH WITH DISSIPATION NEAR 72H.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY EXPOSED LOW LEVEL CIRCULATION (LLC) WITH PERSISTENT CORE CONVECTION OBSCURING THE CENTER. A 150252Z 89GHZ AMSU-B MICROWAVE IMAGE SHOWS FRAGMENTED DEEP CONVECTIVE BANDING LIMITED TO THE SOUTHERN SEMICIRCLE, DEFINED SHALLOW BANDING IN ALL QUADRANTS. ANIMATED TOTAL PRECIPITABLE WATER IMAGERY AND MODEL OUTPUT INDICATE EXTENSIVE DRY AIR PRESENT OVER THE WESTERN AND NORTHERN SEMICIRCLES ENTRAINING INTO THE LLC. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON MSI AND MICROWAVE IMAGERY. THE INITIAL INTENSITY OF 55 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE PGTW DVORAK CURRENT INTENSITY ESTIMATE AND THE CIMSS ADT ESTIMATE.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS BIFURCATED WITH TWO DISTINCT MODEL GROUPINGS. NVGI AND ECMI SHOW A SHARPER SOUTHWARD RECURVE INDUCED BY THE AFOREMENTIONED MIDLATITUDE TROUGH'S PASSAGE WHILE THE REMAINDER OF THE GUIDANCE SUPPORTS THE JTWC FORECAST TRACK. RELIABLE INTENSITY GUIDANCE SHOWS A GENERAL CONSENSUS WITH ALL MEMBERS INDICATING VARIOUS DEGREES OF WEAKENING THROUGH THE FORECAST PERIOD RESULTING IN MEDIUM CONFIDENCE.

THE AREA OF CONVECTION (REMNANTS OF TC 19S) PREVIOUSLY LOCATED NEAR 15.3S 37.3E IS NOW LOCATED NEAR 18.5S 37.5E, APPROXIMATELY 360 KM WEST-NORTHWEST OF EUROPA ISLAND. ANIMATED MULTISPECTRAL SATELLITE IMAGERY INDICATES RAPIDLY WEAKENING CONVECTION WITH A THIN CANOPY OF CIRROSTRATUS CLOUDS OBSCURING THE LOW-LEVEL CIRCULATION CENTER (LLCC). A 151124Z AMSR2 89GHZ COLOR COMPOSITE MICROWAVE IMAGE DEPICTS VERY ISOLATED DEEP CONVECTION WITH SHALLOW BANDING WRAPPING INTO A DEFINED LLCC. A 150619Z ASCAT-B IMAGE SHOWS AN ELONGATED CIRCULATION WITH PREDOMINANTLY 15-25 KNOT WINDS EXCEPT FOR A SMALL PATCH OF 30-35 KNOT WINDS OVER THE EASTERN QUADRANT. UPPER-LEVEL ANALYSIS INDICATES A FAVORABLE ENVIRONMENT WITH AN ANTICYCLONE POSITIONED TO THE NORTHWEST AND FAIR EQUATORWARD AND POLEWARD OUTFLOW AS WELL AS LOW VERTICAL WIND SHEAR. THE PRIMARY LIMITING FACTOR IS PROXIMITY TO LAND. ECMWF INITIALIZES THIS SYSTEM BETTER THAN GFS AND MAINTAINS A QUASI-STATIONARY MOTION OVER THE NEXT DAY THEN A SLOW DRIFT INLAND OVER MOZAMBIQUE BY TAU 48 AT TROPICAL DEPRESSION STRENGTH. GFS IS NOT HANDLING THE SYSTEM WELL AND SHOWS A WEAK LOW PRESSURE AREA. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 20 TO 25 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1004 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS REMAINS MEDIUM.

THE AREA OF CONVECTION (INVEST 91B) PREVIOUSLY LOCATED NEAR 2.1N 86.5E IS NOW LOCATED NEAR 3.3N 87.1E, APPROXIMATELY 880 KM EAST-SOUTHEAST OF COLOMBO, SRI LANKA. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS LARGE, DISORGANIZED CLUSTERS OF DEEP CONVECTION FALRING OVER A BROAD LOW-LEVEL CIRCULATION. A 151046Z SSMIS 91GHZ COLOR COMPOSITE MICROWAVE IMAGE SHOWS A BROAD, WEAKLY DEFINED LOW-LEVEL CIRCULATION CENTER WITH POORLY-ORGANIZED DEEP CONVECTIVE ORGANIZATION. NUMERICAL MODELS INDICATE SLOW DEVELOPMENT OVER THE NEXT FEW DAYS AS THE DISTURBANCE TRACKS GENERALLY EASTWARD. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 15 TO 20 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1006 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS DOWNGRADED TO LOW.

GLOBAL MODELS ARE IN AGREEMENT THAT 91B WILL TRACK NORTHWARD WITH GFS AND NAVGEM INDICATING INTENSIFICATION TO WARNING CRITERIA WITHIN 72 TO 96 HOURS.

THE AREA OF CONVECTION (INVEST 91S) PREVIOUSLY LOCATED NEAR 12.1S 50.5E IS NOW LOCATED NEAR 12.5S 50.6E, APPROXIMATELY 640 KM NORTH OF TOAMASINA, MADAGASCAR. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS A FULLY-EXPOSED, WELL-DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC) WITH DISORGANIZED, FLARING CONVECTION. A 150945Z AMSR2 89GHZ COLOR COMPOSITE MICROWAVE IMAGE SHOWS FRAGMENTED, SHALLOW BANDING WRAPPING INTO THE DEFINED LLCC. A 150617Z ASCAT-B IMAGE REVEALS AN ELONGATED, WEAK CIRCULATION WITH 15 TO 20 KNOT WINDS. UPPER-LEVEL ANALYSIS INDICATES A MARGINAL ENVIRONMENT WITH MODERATE TO HIGH (20-25 KNOTS) VERTICAL WIND SHEAR AND WEAKLY DIFFLUENT FLOW ALOFT. SST VALUES ARE CONDUCIVE AT 28C. NUMERICAL MODEL GUIDANCE INDICATES THE SYSTEM WILL TRACK SOUTHWARD ALONG THE EAST COAST OF MADAGASCAR THEN TRACK OVER NORTHERN MADAGASCAR BETWEEN TAU 24 TO TAU 36 WITH NO SIGNIFICANT DEVELOPMENT EXPECTED. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 15 TO 20 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1007 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS DOWNGRADED TO LOW.

GLOBAL MODELS, NAMELY ECMWF, ARE INDICATING A SHORT LIVED OPPORTUNITY FOR INTENSIFICATION BEFORE THE SYSTEM MAKES LANDFALL OVER NORTHERN MADAGASCAR.