(3) AN AREA OF CONVECTION (INVEST 99W) HAS PERSISTED NEAR
15.3N 140.6E, APPROXIMATELY 258 NM WEST-NORTHWEST OF GUAM. ANIMATED
ENHANCED INFRARED SATELLITE IMAGERY AND A 170943Z SSMIS 91GHZ
MICROWAVE PASS DEPICT DEEP FLARING CENTRAL CONVECTION AND
UNORGANIZED, SHALLOW, AND FRAGMENTED BANDING AROUND THE LOW LEVEL
CIRCULATION CENTER. UPPER-LEVEL ANALYSIS REVEALS GOOD DIFFLUENCE
ALOFT AND LIGHT TO MODERATE VERTICAL WIND SHEAR OF 10 TO 20 KNOTS.
MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 20 TO 25 KNOTS.
MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1004 MB. THE
POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE
WITHIN THE NEXT 24 HOURS IS LOW.
WTPN21 PGTW 171600
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE FORMATION ALERT//
RMKS/
1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN
300 NM EITHER SIDE OF A LINE FROM 14.9N 139.8E TO 17.6N 148.6E
WITHIN THE NEXT 06 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 20 TO 25 KNOTS. METSAT
IMAGERY AT 171200Z INDICATES THAT A CIRCULATION CENTER IS LOCATED
NEAR 15.2N 140.6E. THE SYSTEM IS MOVING EAST-NORTHEASTWARD AT 06
KNOTS.
2. REMARKS: THE AREA OF CONVECTION (INVEST 99W) PREVIOUSLY LOCATED
NEAR 15.0N 140.0E, IS NOW LOCATED NEAR 15.2N 140.6E, APPROXIMATELY
250 NM WEST-NORTHWEST OF ANDERSEN AFB, GUAM. ANIMATED ENHANCED
INFRARED SATELLITE IMAGERY DEPICTS INCREASED CONVECTION ASSOCIATED
WITH A DEFINED AND PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER
(LLCC). A 171143Z PARTIAL ASCAT PASS SHOWED THE WESTERN SEMI-CIRCLE
OF THE LLCC WITH 20 KNOT WINDS WRAPPING AROUND THE WESTERN SIDE INTO
THE 30 TO 35 KNOT WESTERLY SURGE TO THE SOUTH. AN OLDER 170843Z
CORIOLIS PASS SHOWED SHALLOW FRAGMENTED BANDING ALONG THE WESTERN
SIDE FEEDING THE BULK OF CONVECTION SHEARED JUST WEST OF CENTER.
UPPER LEVEL ANALYSIS INDICATES A MOSTLY FAVORABLE ENVIRONMENT WITH
10 TO 20 KNOT EASTERLY VERTICAL WIND SHEAR BEING OFFSET BY STRONG
DIVERGENT OUTFLOW. DYNAMIC MODE GUIDANCE SHOWS CONTINUED DEVELOPMENT
OF THIS DISTURBANCE AS IT TRACKS NORTHEASTWARD. MAXIMUM SUSTAINED
SURFACE WINDS ARE ESTIMATED AT 20 TO 25 KNOTS. MINIMUM SEA LEVEL
PRESSURE IS ESTIMATED TO BE NEAR 1004 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
181600Z.//
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