WTXS21 PGTW 190100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/TROPICAL CYCLONE FORMATION ALERT (INVEST 97S)// RMKS/ 1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN 120 NM EITHER SIDE OF A LINE FROM 12.8S 76.3E TO 16.1S 76.1E 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 27 TO 33 KNOTS. METSAT IMAGERY AT 190000Z INDICATES THAT A CIRCULATION CENTER IS LOCATED NEAR 12.9S 76.3E. THE SYSTEM IS MOVING SOUTH-SOUTHEASTWARD AT 04 KNOTS. 2. REMARKS: THE AREA OF CONVECTION (INVEST 97S) PREVIOUSLY LOCATED NEAR 12.5S 76.1E IS NOW LOCATED NEAR 12.9S 76.3E, APPROXIMATELY 401 NM SOUTHEAST OF DIEGO GARCIA. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY (EIR) DEPICTS A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) LOCATED APPROXIMATELY 400 NM SOUTHEAST OF DIEGO GARCIA. DEEP CONVECTION HAS BEEN PATCHY WITH LIMITED COVERAGE, PRIMARILY CONFINED SOUTH AND WEST OF THE CENTER DUE TO NORTHEASTERLY WIND SHEAR. WHILE THE VORTEX REMAINS VERTICALLY TILTED DUE TO THIS SHEAR, THE LLCC HAS BECOME BETTER DEFINED AND MORE SYMMETRIC IN RECENT HOURS. AN 182230Z SSMIS MICROWAVE IMAGE REVEALED TIGHTLY COILED LOW-LEVEL CLOUD BANDS AROUND THE LLCC. AN EARLIER 181611Z ASCAT PASS SHOWED 25-30 KNOT WIND BELTS TO THE NORTH AND SOUTH OF THE LLCC, THOUGH THE MAXIMUM WINDS REMAINED SOMEWHAT DISTANT (ABOUT 80 NM) FROM THE CENTER, INDICATING THAT AN ORGANIZED INNER CORE WIND FIELD HAS NOT YET DEVELOPED. THE ENVIRONMENT IS GENERALLY FAVORABLE FOR DEVELOPMENT WITH WARM SEA SURFACE TEMPERATURES (28-29 DEGREES CELSIUS), MODERATE POLEWARD OUTFLOW ALOFT, AND A REGION OF DEEP MOISTURE ENCOMPASSING THE LLCC. MODERATE VERTICAL WIND SHEAR (15-20 KNOTS) IS THE PRIMARY LIMITING FACTOR SHORT-TERM. AS THE SYSTEM BEGINS TO MOVE SOUTHWARD, IT WILL ENTER A REGION OF LIGHTER VERTICAL SHEAR OVER THE NEXT 24 HOURS. WITH THE WELL-DEFINED LLCC AS A FOUNDATION, THIS IS EXPECTED TO ALLOW THE VORTEX TO BECOME MORE VERTICALLY ALIGNED, WITH DEEP CONVECTION GRADUALLY SYMMETRIZING AROUND THE LLCC. PHYSICAL AND AI-BASED MODELS ALIKE ARE DEVELOPING A STRONG CONSENSUS FOR SHORT-TERM DEVELOPMENT. THE ECMWF AND GFS GLOBAL MODELS SHOW THE CYCLONE REACHING WARNING THRESHOLD IN 24 TO 36 HOURS, THE HIGH-RESOLUTION HWRF AND HAFS-A MODELS IN 12 TO 24 HOURS, AND THE GOOGLE DEEPMIND ENSEMBLE MEAN IN 12 TO 24 HOURS. THESE MODELS ALSO GENERALLY AGREE ON A SHORT-TERM SOUTHWARD TRACK, BENDING SOUTH-SOUTHWESTWARD AND THEN SOUTHWESTWARD OVER THE NEXT 48 HOURS. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 27 TO 33 KNOTS.MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 998 MB. THEPOTENTIAL 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 200100Z.// NNNN