WTPN21 PGTW 051930
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
150 NM EITHER SIDE OF A LINE FROM 15.0N 146.6E TO 21.8N 146.5E
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 051800Z INDICATES THAT A CIRCULATION CENTER IS LOCATED
NEAR 15.2N 146.6E. THE SYSTEM IS MOVING NORTHWARD AT 10 KNOTS.
2. REMARKS: THE AREA OF CONVECTION (INVEST 99W) PREVIOSULY LOCATED NEAR 
11.8N 148.6E IS NOW LOCATED NEAR 15.2N 146.6E, APPROXIMATELY 132NM 
NORTHEAST OF GUAM. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A 
CONSOLIDATING LOW LEVEL CIRCULATION CENTER WITH MODERATE FLARING 
CONVECTION IN THE NORTHERN PERIPHERY OF THE SYSTEM. A 051409Z OSCAT3 
SCATTEROMETER PASS REVEALS MODERATE TO STRONG (25-30 KNOTS) WINDS IN THE 
NORTHERN QUADRANT DIRECTLY ASSOCIATED WITH THE AFOREMENTIONED ASSOCIATED 
CONVECTION, HOWEVER, 15-20 KNOT WINDS HAVE CONTINUED TO LOOSELY WRAP INTO 
THE LOW-LEVEL CIRCULATION CENTER OVER THE PAST 24-36 HOURS. ENVIRONMENTAL 
ANALYSIS INDICATED THAT 99W IS IN AN OVERALL MARGINAL ENVIRONMENT FOR 
FURTHER DEVELOPMENT WITH WARM (29-30C) SEA SURFACE TEMPERATURES, WEAK 
RADIAL OUTFLOW, AND LOW TO MODERATE (15 TO 20 KNOTS) VERTICAL WIND SHEAR 
(VWS). THE ECMWF AND GFS ENSEMBLE MODELS ARE IN GOOD AGREEMENT THAT 99W 
WILL GENERALLY TRACK NORTHWARD OVER THE NEXT 24-36 HOURS. GLOBAL 
DETERMINISTIC MODELS ARE IN GOOD AGREEMENT WITH 99W TRACKING NORTHWARD 
WITH SLOW AND STEADY INTENSIFICATION IN THE NEXT 24-36 HOURS TO 23-28 
KNOTS. 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 
061930Z.//
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