WTXS21 PGTW 152100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/TROPICAL CYCLONE FORMATION ALERT (INVEST 99S)// RMKS/ 1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN 140 NM EITHER SIDE OF A LINE FROM 12.1S 67.9E TO 13.4S 61.4E WITHIN THE NEXT 12 TO 24 HOURS. AVAILABLE DATA DOES NOT JUSTIFY ISSUANCE OF NUMBERED TROPICAL CYCLONE WARNINGS AT THIS TIME. WINDS IN THE AREA ARE ESTIMATED TO BE 28 TO 33 KNOTS. METSAT IMAGERY AT 151800Z INDICATES THAT A CIRCULATION CENTER IS LOCATED NEAR 12.3S 67.5E. THE SYSTEM IS MOVING WEST-SOUTHWESTWARD AT 14 KNOTS. 2. REMARKS: THE AREA OF CONVECTION (INVEST 99S) PREVIOUSLY LOCATED NEAR 11.9S 68.9E IS NOW LOCATED NEAR 12.3S 67.5E, APPROXIMATELY 407NM SOUTHWEST OF DIEGO GARCIA. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY AND A 151152Z SSMIS 91GHZ MICROWAVE IMAGE SHOW A CONSOLIDATING LOW LEVEL CIRCULATION (LLC) OBSCURED BY FLARING CONVECTION SHEARED TO THE WEST WITH CONVECTIVE BANDING WRAPPING INTO THE CIRCULATION FROM THE SOUTH. A 1642Z ASCAT METOP-B IMAGE SHOWS 25- 30 KNOT WINDS WRAPPING INTO THE LLC FROM THE SW QUADRANT. INVEST 99S IS IN A FAVORABLE ENVIRONMENT FOR DEVELOPMENT WITH GOOD OUTFLOW ALOFT, LOW TO MODERATE (15-25KTS) VERTICAL WIND SHEAR, AND WARM (28- 29C) SEA SURFACE TEMPERATURES. GLOBAL MODELS ARE IN GOOD AGREEMENT THAT INVEST 99S WILL CONTINUE TO TRACK WEST-SOUTHWESTWARD AS IT SLOWLY INTENSIFIES. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 28 TO 33 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 IS HIGH. 3. THIS ALERT WILL BE REISSUED, UPGRADED TO WARNING OR CANCELLED BY 162100Z.// NNNN