Indian Ocean: 3 Invest Areas: Invest 93S up-graded to Medium//Invest 91B over the BOB//Invest 94S: slow development expected,19/09utc

JTWC IS ISSUING 3HOURLY SATELLITE BULLETINS ON INVEST 93S, INVEST 91B AND INVEST 94S.

19/0920UTC.

THE AREA OF CONVECTION (INVEST 93S) PREVIOUSLY LOCATED NEAR 10.9S 120.1E IS NOW LOCATED NEAR 11.7S 118.7E, APPROXIMATELY 570 KM NORTH-NORTHWEST OF BROWSE ISLAND. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY (EIR) AND A 182000Z SSMIS 91GHZ MICROWAVE PASS DEPICT A DEEP CONVECTIVE CORE FLARING AND OBSCURING A LOW LEVEL CIRCULATION (LLC). THE ENVIRONMENT IS CONDUCIVE FOR DEVELOPMENT WITH GOOD POLEWARD OUTFLOW ONLY EXPECTED TO GET BETTER AS 93S TAPS INTO THE UPPER LEVEL WESTERLIES ASSOCIATED WITH A MID-LATITUDE TROUGH PASSING TO THE SOUTH, LOW (5-15KT)VERTICAL WIND SHEAR AND WARM (30- 31C) SEA SURFACE TEMPERATURES. GLOBAL NUMERICAL MODELS AGREE THAT INVEST 93S WILL CONTINUE ON ITS WEST SOUTHWESTWARD TRACK HOWEVER, THE DEVELOPMENT TIMELINES HAVE SIGNIFICANT DISPARITY BETWEEN GFS AND ECWMF, WITH ECMWF HOLDING 93S AS A TROPICAL DEPRESSION STRENGTH SYSTEM BEYOND 72 HOURS, WHILE GFS ACCELERATES INTENSIFICATION TO A TROPICAL STORM WITHIN 36-48 HOURS. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 20 TO 25 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1002 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS UPGRADED TO MEDIUM.

GLOBAL NUMERICAL MODELS AGREE THAT INVEST 93S WILL CONTINUE ON ITS WEST SOUTHWESTWARD TRACK HOWEVER, THE DEVELOPMENT TIMELINES HAVE SIGNIFICANT DISPARITY BETWEEN GFS AND ECWMF, WITH ECMWF HOLDING 93S AS A TROPICAL DEPRESSION STRENGTH SYSTEM BEYOND 72 HOURS, WHILE GFS ACCELERATES INTENSIFICATION TO A TROPICAL STORM WITHIN 36-48 HOURS.

THE AREA OF CONVECTION (INVEST 91B) PREVIOUSLY LOCATED NEAR 7.5N 91.1E IS NOW LOCATED NEAR 7.8N 91.3E, APPROXIMATELY 520KM NORTH-NORTHEAST OF PORT BLAIR. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY (EIR) AND A 181213Z SSMIS 91GHZ MICROWAVE PASS DEPICT DISORGANIZED CONVECTION OBSCURING A BROAD LOW LEVEL CIRCULATION. THE ENVIRONMENT IS CONDUCIVE FOR DEVELOPMENT WITH FAIR EQUATORWARD OUTFLOW, LOW (10-15 KT) VERTICAL WIND SHEAR (VWS) ON THE NORTHEAST SIDE, AND MODERATE TO HIGH (20-30KT) SHEAR TO THE SOUTH, OFFSET BY WARM (29-30C) SSTS. GLOBAL MODELS AGREE THAT INVEST 91B WILL TRACK NORTHWARD OVER THE NEXT 24-48 HOURS. HOWEVER, THE DEVELOPMENT TIMELINES HAVE SIGNIFICANT DISPARITY BETWEEN GFS AND ECWMF. ECWMF AND THE ENSEMBLE KEEP THE SYSTEM UNDER TROPICAL STORM STRENGTH THROUGH 48-72 HOURS, WHILE GFS AND THE ENSEMBLE ACCELERATE THE INTENSIFICATION TO TROPICAL STORM STRENGTH WITHIN 24-36 HOURS. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 15 TO 20 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1008 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS REMAINS LOW.

GLOBAL NUMERICAL MODELS AGREE THAT INVEST 93S WILL CONTINUE ON ITS WEST SOUTHWESTWARD TRACK HOWEVER, THE DEVELOPMENT TIMELINES HAVE SIGNIFICANT DISPARITY BETWEEN GFS AND ECWMF, WITH ECMWF HOLDING 93S AS A TROPICAL DEPRESSION STRENGTH SYSTEM BEYOND 72 HOURS, WHILE GFS ACCELERATES INTENSIFICATION TO A TROPICAL STORM WITHIN 36-48 HOURS.

AN AREA OF CONVECTION (INVEST 94S) HAS PERSISTED NEAR 7.3S 94.5E, APPROXIMATELY 590 KM NORTHWEST OF COCOS ISLAND. EIR AND A 181209Z SSMIS 91GHZ MICROWAVE PASS DEPICT FRAGMENTED CONVECTIVE BANDING FORMING NORTH AND SOUTHEAST OF A BROAD LLC. UPPER-AIR ANALYSIS SHOWS THAT INVEST 94S IS UNDER HIGH (30-40KT) VWS, WITH SLIGHT EQUATORWARD OUTFLOW OFFSET BY FAVORABLE (29-30C) SEA SURFACE TEMPERATURES. GLOBAL NUMERICAL MODELS AGREE THAT INVEST 94S WILL GRADUALLY DEVELOP AS THE SYSTEM TRACKS WEST-SOUTHWESTWARD BUT IS NOT EXPECTED TO REACH TROPICAL STORM STRENGTH UNTIL BEYOND 72-96 HOURS. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 15-20 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 LOW.

GLOBAL NUMERICAL MODELS AGREE THAT INVEST 94S WILL GRADUALLY DEVELOP AS THE SYSTEM TRACKS WEST-SOUTHWESTWARD BUT IS NOT EXPECTED TO REACH TROPICAL STORM STRENGTH UNTIL BEYOND 72-96 HOURS.