WTPN21 PGTW 211230 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/TROPICAL CYCLONE FORMATION ALERT (INVEST 99W)// RMKS/ 1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN 140 NM EITHER SIDE OF A LINE FROM 11.1N 151.6E TO 13.6N 146.6E 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 18 TO 23 KNOTS. METSAT IMAGERY AT 211200Z INDICATES THAT A CIRCULATION CENTER IS LOCATED NEAR 11.2N 151.5E. THE SYSTEM IS MOVING WEST-NORTHWESTWARD AT 11 KNOTS. 2. REMARKS: THE AREA OF CONVECTION (INVEST 99W) PREVIOUSLY LOCATED NEAR 10.3N 154.6E IS NOW LOCATED NEAR 11.2N 151.5E. A 211052Z METOP- B PASS SHOWS THAT A DISCREET LOW-LEVEL CIRCULATION CENTER (LLCC) HAS CONSOLIDATED OVER THE PAST 12 HOURS, WITH A SMALL BUT WELL-DEFINED CIRCULATION SURROUNDED BY 12-17 KNOT WINDS. A BAND OF 20-25 KNOT WINDS EXTENDS FROM SOUTH TO SOUTHEAST OF THE CENTER. ANIMATED ENHANCED INFRARED IMAGERY AND A 210811Z SSMIS 91GHZ IMAGE DEPICTS FLARING DISORGANIZED CONVECTION PRIMARILY ON THE SOUTH AND EAST SIDE OF THE ROTATION. ENVIRONMENTAL ANALYSIS INDICATES A FAVORABLE ENVIRONMENT FOR DEVELOPMENT WITH A COMBINATION OF STRONG OUTFLOW ALOFT WITH A POINT SOURCE OR ANTICYCLONE ALOFT DIRECTION OVERHEAD THE LLCC, LOW (10 KT) VERTICAL WIND SHEAR (VWS) AND VERY WARM (30- 31C) SEA SURFACE TEMPERATURES (SST). GLOBAL MODELS ARE GOOD IN AGREEMENT THAT INVEST 99W WILL CONTINUE TRACKING NORTHWESTWARD OVER THE NEXT 24-48 HOURS HOWEVER, THEY ARE SPLIT ON THE DEGREE OF DEVELOPMENT. GFS, ITS ENSEMBLE, AND NAVGEM ARE THE MOST AGGRESSIVE, INDICATING FAIRLY RAPID CONSOLIDATION AND INTENSIFICATION, REACHING TROPICAL DEPRESSION STRENGTH WITHIN THE NEXT 24 HOURS AND TROPICAL STORM STRENGTH WITHIN THE NEXT 48 HOURS OR LESS, PRIOR TO PASSAGE THROUGH THE MARIANAS ISLAND CHAIN. ECMWF AND ITS ENSEMBLE ARE MUCH MORE RESERVED, INDICATING LITTLE TO NO DEVELOPMENT UNTIL AFTER TAU 48, WELL TO THE WEST OF THE MARIANAS. OF NOTE, THE ASCAT PASS VERIFIED THE 1200Z GFS MODEL FORECAST POSITION AND WIND FIELD WITH HIGH CONFIDENCE, LENDING INCREASED CONFIDENCE TO THE GFS FORECAST. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 18 TO 23 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1005 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 221230Z. // NNNN