(1) AN AREA OF CONVECTION (INVEST 98W) HAS PERSISTED NEAR
15.0N 147.8E, APPROXIMATELY 205 NM EAST-NORTHEAST OF GUAM. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY AND A 012358Z AMSU 89 GHZ IMAGE
DEPICT A BROAD, WEAK LOW-LEVEL CIRCULATION CENTER WITH DISORGANIZED,
FLARING DEEP CONVECTION ALONG THE OUTER PERIPHERY. A RECENT
SCATTEROMETRY PASS REVEALED 15 TO 20 KNOT WINDS ALONG THE SOUTHEAST
PERIPHERY OF THE SYSTEM, AND WEAKER WINDS ELSEWHERE. UPPER-LEVEL
ANALYSIS INDICATES A FAVORABLE ENVIRONMENT FOR DEVELOPMENT WITH GOOD
OUTFLOW AND LOW (10 TO 15 KNOTS) VERTICAL WIND SHEAR. GLOBAL MODEL
GUIDANCE IS IN FAIRLY GOOD AGREEMENT ON THE GRADUAL DEVELOPMENT OF
THE SYSTEM OVER THE NEXT 36 TO 48 HOURS IS IT SLOWLY TRACKS
NORTHWARD. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 15 TO 20
KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1003 MB.
THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE
WITHIN THE NEXT 24 HOURS IS LOW.
B. TROPICAL DISTURBANCE SUMMARY:
(1) THE AREA OF CONVECTION (INVEST 98W) PREVIOUSLY LOCATED
NEAR 15.0N 147.8E, IS NOW LOCATED NEAR 18.2N 148.5E, APPROXIMATELY
365 NM NORTH-NORTHEAST OF GUAM. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY DEPICTS A VERY BROAD AREA OF CYCLONIC CIRCULATION WITH
FLARING DEEP CONVECTION ALONG THE OUTER PERIPHERY. A 022339Z ASCAT
PASS ALSO REVEALS THE BROAD NATURE OF THE CIRCULATION, WITH WEAK
WINDS OBSERVED NEAR THE CENTER AND THE STRONGEST WINDS (15 TO 20
KNOTS) EXTENDING 300 TO 400 NM FROM THE CENTER. UPPER-LEVEL ANALYSIS
CONTINUES TO INDICATE A FAVORABLE ENVIRONMENT FOR DEVELOPMENT WITH
IMPROVING OUTFLOW AND LOW-MODERATE (15 TO 20 KNOTS) VERTICAL WIND
SHEAR. GLOBAL MODEL GUIDANCE IS IN FAIRLY GOOD AGREEMENT ON THE
GRADUAL DEVELOPMENT OF THE SYSTEM INTO A MONSOON DEPRESSION OVER THE
NEXT 24 TO 36 HOURS AS IT TRACKS NORTHWARD. MAXIMUM SUSTAINED
SURFACE WINDS ARE ESTIMATED AT 15 TO 20 KNOTS. MINIMUM SEA LEVEL
PRESSURE IS ESTIMATED TO BE NEAR 1002 MB. BASED ON THE POTENTIAL FOR
THE SYSTEM TO CONSOLIDATE INTO A TROPICAL CYCLONE BEYOND 36 HOURS,
DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24
HOURS IS UPGRADED TO MEDIUM.
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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