WTXS21 PGTW 270900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/TROPICAL CYCLONE FORMATION ALERT (INVEST 98S)// RMKS/ 1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN 120 NM EITHER SIDE OF A LINE FROM 10.0S 65.2E TO 10.3S 68.8E 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 270830Z INDICATES THAT A CIRCULATION CENTER IS LOCATED NEAR 10.2S 65.6E. THE SYSTEM IS MOVING EAST-SOUTHEASTWARD AT 04 KNOTS. 2. REMARKS: THE AREA OF CONVECTION (INVEST 98S) PREVIOUSLY LOCATED NEAR 9.9S 64.9E IS NOW LOCATED NEAR 10.2S 65.6E, APPROXIMATELY 439 NM WEST-SOUTHWEST OF DIEGO GARCIA. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS A WELL-DEFINED LOW LEVEL CIRCULATION CENTER (LLCC) LOCATED NEAR THE NORTHEAST EDGE OF A MASS OF CONVECTION THAT HAS EXHIBITED PULSING BURSTS DURING THE PAST 6 HOURS. SATELLITE IMAGERY INDICATES THAT THE MID-LEVEL CIRCULATION CENTER IS DISPLACED WEST OF THE LLCC AS A RESULT OF 10-15 KTS OF EASTERLY VERTICAL WIND SHEAR, AND THE LLCC IS PARTIALLY EXPOSED ON THE NORTHEAST SIDE. HOWEVER, A 270533Z ASCAT-C IMAGE REVEALS A COMPACT CIRCULATION THAT HAS SEEN ITS RADIUS OF MAXIMUM WIND CONTRACT SUBSTANTIALLY TO AROUND 20 NM DURING THE PAST 12 HOURS, WITH A BAND OF 30 KT WINDS ENCOMPASSING THE ENTIRE NORTHWESTERN SEMICIRCLE. HEALTHY UPPER-LEVEL OUTFLOW IS OBSERVED IN ALL QUADRANTS EXCEPT NORTHEAST. INVEST 98S IS LOCATED IN A MOSTLY FAVORABLE ENVIRONMENT WITH SEA SURFACE TEMPERATURES AROUND 29C AND LIGHT-MODERATE VERTICAL WIND SHEAR. WATER VAPOR SATELLITE IMAGERY AND PRECIPITABLE WATER DATA INDICATE A BAND OF DRY AIR LOCATED ABOUT 200 NM SOUTHWEST OF THE SYSTEM, BUT DOES NOT APPEAR TO BE WRAPPING INTO THE CIRCULATION AT PRESENT. NUMERICAL MODELS HAVE MIXED OPINIONS ON DEVELOPMENT, WITH MOST SHOWING ONLY SLIGHT INTENSIFICATION OF 98S IN THE SHORT TERM. HOWEVER, MOST MODELS DEPICT 98S WITH A BROADER AND WEAKER CIRCULATION THAN IS BEING OBSERVED, SUGGESTING THAT DEVELOPMENT CHANCES ARE HIGHER. INVEST 98S IS EXPECTED TO TRACK EAST-SOUTHEASTWARD AND THEN TURN EASTWARD UNDER THE INFLUENCE OF A WESTERLY WIND BAND TO ITS NORTH. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 28 TO 33 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 HIGH. 3. THIS ALERT WILL BE REISSUED, UPGRADED TO WARNING OR CANCELLED BY 280900Z.// NNNN