WTXS21 PGTW 201830 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/TROPICAL CYCLONE FORMATION ALERT (INVEST 90S)// RMKS/ 1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN 80 NM EITHER SIDE OF A LINE FROM 9.5S 84.2E TO 10.5S 80.3E 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 23 TO 27 KNOTS. METSAT IMAGERY AT 201700Z INDICATES THAT A CIRCULATION CENTER IS LOCATED NEAR 9.5S 84.2E. THE SYSTEM IS MOVING SOUTHWARD AT 10 KNOTS. 2. REMARKS: THE AREA OF CONVECTION (INVEST 90S) PREVIOUSLY LOCATED NEAR 9.9S 84.1E IS NOW LOCATED NEAR 9.5S 84.2E. ANIMATED ENHANCED INFRARED IMAGERY DEPICTS AN EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) WITH FLARING CONVECTION DISPLACED TO THE SOUTH. A 1454 ASCAT- A IMAGE SHOWS WRAPPING 25 KT WINDS IN THE SOUTHERN SEMICIRCLE. ENVIRONMENTAL ANALYSIS REVEALS MARGINALLY UNFAVORABLE CONDITIONS WITH HIGH (30-40 KT) VWS OFFSET BY PRONOUNCED RADIAL OUTFLOW AND HIGH SEA SURFACE TEMPERATURES (29-30C). GLOBAL MODELS ARE IN AGREEMENT THAT INVEST 90S WILL TRACK TO THE SOUTHWEST WITH THE GFS DETERMINISTIC MODEL SHOWING THE MOST AGGRESSIVE PREDICTION. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 23 TO 27 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 HIGH. 3. THIS ALERT WILL BE REISSUED, UPGRADED TO WARNING OR CANCELLED BY 211830Z. // NNNN