WTPN21 PGTW 040430
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE FORMATION ALERT//
RMKS/
1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN
200 NM EITHER SIDE OF A LINE FROM 18.1N 146.9E TO 24.3N 148.2E
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 IMAGERY AT
040400Z INDICATES THAT A CIRCULATION CENTER IS LOCATED NEAR 18.8N
146.8E. THE SYSTEM IS MOVING NORTHWARD AT 04 KNOTS.
2. REMARKS: THE AREA OF CONVECTION (INVEST 98W) PREVIOUSLY LOCATED
NEAR 18.2N 148.5E IS NOW LOCATED NEAR 18.8N 146.8E, APPROXIMATELY
220 NM NORTH-NORTHEAST OF SAIPAN. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) DEPICTS A MONSOON DEPRESSION WITH DEEP CONVECTIVE
BANDING DISPLACED OVER THE SOUTH AND SOUTHEAST PERIPHERY OF AN ILL-
DEFINED, BROAD CENTER. MSI ALSO SHOWS SMALL MESOVORTICES ROTATING
AROUND THE PERIPHERY OF THE MONSOON DEPRESSION; THE CURRENT POSITION
IS BASED ON THE CENTROID RATHER THAN ON THESE SHORT-LIVED
MESOVORTICES. A 032321Z ASCAT IMAGE SHOWS A BAND OF 30-KNOT WINDS
OVER THE SOUTHERN SEMI-CIRCLE AND A RADIUS OF MAXIMUM WINDS OF
APPROXIMATELY 115 NM. A 040003Z METOP-A 89GHZ IMAGE SHOWS FRAGMENTED
BANDING OVER THE SOUTHERN SEMI-CIRCLE WRAPPING INTO THE SOUTHEAST
QUADRANT OF THE LOW-LEVEL CIRCULATION CENTER WITH SHALLOW BANDING
ELSEWHERE. UPPER-LEVEL ANALYSIS CONTINUES TO INDICATE A FAVORABLE
ENVIRONMENT FOR DEVELOPMENT WITH IMPROVING OUTFLOW AND LOW TO
MODERATE (15 TO 20 KNOTS) VERTICAL WIND SHEAR. DYNAMIC MODEL
GUIDANCE SHOWS A GENERAL POLEWARD TRACK MOVEMENT WITH SLOW
CONSOLIDATION INTO A TROPICAL CYCLONE FORECAST WITHIN THE NEXT ONE
TO TWO DAYS. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 25 TO
30 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1000
MB. BASED ON THE INCREASED POTENTIAL FOR THE SYSTEM TO CONSOLIDATE
INTO A TROPICAL CYCLONE, 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
050430Z.//
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