WTPS21 PGTW 171830
MSGID/GENADMIN/NAVPACMETOCCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE FORMATION ALERT//
RMKS/
1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN
145 NM EITHER SIDE OF A LINE FROM 12.9S 157.9E TO 17.6S 161.7E
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 25 TO 30 KNOTS. METSAT IM-
AGERY AT 171200Z INDICATES THAT A CIRCULATION CENTER IS LOCATED
NEAR 13.4S 158.3E.  THE SYSTEM IS MOVING SOUTHEASTWARD AT 11
KNOTS.
2. REMARKS: THE AREA OF CONVECTION PREVIOUSLY LOCATED NEAR 12.7S
158.4E, IS NOW LOCATED NEAR 13.4S 158.3E, APPROXIMATELY 255 NM
SOUTH-SOUTHWEST OF HONIARA, SOLOMON ISLANDS. RECENT ANIMATED
INFRARED SATELLITE IMAGERY SHOWS THAT A BURST OF DEEP CONVECTION
HAS DEVELOPED OVER LOW LEVEL CIRCULATION CENTER (LLCC) OVER THE
PAST 06 HOURS. ADDITIONALLY, A 171439Z AMSU MICROWAVE IMAGE
INDICATES THE LLCC IS CONSOLIDATING. THE MOST RECENT 170737Z
QUIKSCAT PASS SHOWS 20-KNOT UNFLAGGED WINDS AT THE CORE. AN
ANTICYCLONE IS SITUATED ALOFT OF THE DISTURBANCE AND IS
PROVIDING EXCELLENT DIFFLUENCE ALOFT AND LOW VERTICAL WIND SHEAR,
AND COULD FACILITATE RAPID DEVELOPMENT. MAXIMUM SUSTAINED SURFACE
WINDS ARE ESTIMATED AT 20 TO 25 KNOTS. MINIMUM SEA LEVEL PRESSURE
IS ESTIMATED TO BE NEAR 1005 MB. DUE TO THE IMPROVED CONVECTIVE
SIGNATURE OVER THE LLCC AND THE FAVORABLE UPPER LEVEL ENVIRONMENT,
THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE
WITHIN THE NEXT 24 HOURS IS UPGRADED TO GOOD.
3. THIS ALERT WILL BE REISSUED, UPGRADED TO WARNING OR CANCELLED
BY 181830Z.//