WTPN21 PGTW 250530
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
120 NM EITHER SIDE OF A LINE FROM 11.2N 113.8E TO 12.7N 110.6E
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 250000Z INDICATES THAT A CIRCULATION CENTER IS LOCATED
NEAR 11.2N 113.7E. THE SYSTEM IS MOVING WESTWARD AT 12 KNOTS.
2. REMARKS: THE AREA OF CONVECTION (INVEST 99W) PREVIOUSLY LOCATED 
NEAR 10.5N 117.8E IS NOW LOCATED NEAR 11.2N 113.7E, APPROXIMATELY 
311 NM WEST-NORTHWEST OF PUERTO PRINCESA, PHILIPPINES. ANIMATED 
MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS CURVED DEEP CONVECTIVE 
BANDING THAT APPEARS TO BE WRAPPING INTO A PARTIALLY-EXPOSED LLC. 
THIS BANDING CAN ALSO BE SEEN IN A 242334Z 91GHZ SSMIS IMAGE, BUT A 
250008Z ASCAT-A IMAGE INDICATES THAT THE BROAD AREA OF 20-25 KT 
WINDS UNDER THE BANDING IS PART OF THE COLD SURGE EVENT TO THE NORTH 
AND NOT ASSOCIATED WITH THE BROAD CIRCULATION. ENVIRONMENTAL 
ANALYSIS INDICATES FAVORABLE CONDITIONS FOR DEVELOPMENT, WITH 
MODERATE EQUATORWARD OUTFLOW, LOW (10-15 KTS) VERTICAL WIND SHEAR 
(VWS) AND WARM (29-30 C) SEA SURFACE TEMPERATURES (SST). GLOBAL 
NUMERICAL MODELS ARE IN GOOD AGREEMENT THAT INVEST 99W WILL TRACK 
WEST-NORTHWESTWARD AND MAKE LANDFALL OVER VIETNAM WITHIN THE NEXT 36 
HOURS. THE MODELS INDICATE THE POSSIBILITY OF A WEAK TROPICAL 
DEPRESSION BEFORE LANDFALL, BUT THE CURRENT TRACK SPEED OF INVEST 
99W, WHICH IS FASTER THAN IN MODEL GUIDANCE, INDICATES THE SYSTEM 
MAY MAKE LANDFALL SOONER WITH LESS TIME OVER WATER TO REACH WARNING 
CRITERIA. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 18 TO 23 
KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1009 MB. 
THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE 
WITHIN THE NEXT 24 HOURS IS UPGRADED TO HIGH.
3. THIS ALERT WILL BE REISSUED, UPGRADED TO WARNING OR CANCELLED BY 
260530Z.
//
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