WTPN21 PGTW 171330
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE FORMATION ALERT (INVEST 91W)//
RMKS/
1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN
175 NM EITHER SIDE OF A LINE FROM 27.3N 157.8E TO 33.5N 162.4E
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 171200Z INDICATES THAT A CIRCULATION CENTER IS LOCATED
NEAR 27.6N 157.8E. THE SYSTEM IS MOVING NORTHWARD AT 06 KNOTS.
2. REMARKS: THE AREA OF CONVECTION (INVEST 91W) PREVIOUSLY LOCATED NEAR
27.1N 156.7E IS NOW LOCATED NEAR 27.6N 157.8E, APPROXIMATELY 700 NM
NORTHWEST OF WAKE ISLAND. RECENT PHASE CLASSIFICATION WORKSHEETS INDICATE
THE SYSTEM HAS TRANSITIONED FROM SUBTROPICAL TO TROPICAL SYSTEM AND THUS
IS NO LONGER CLASSIFIED AS A SUBTROPICAL DEPRESSION. ANIMATED ENHANCED
INFRARED (EIR) SATELLITE IMAGERY DEPICTS A LOW LEVEL CIRCULATION CENTER
(LLCC) THAT HAS BECOME ALIGNED WITH STRONG CONVECTION THAT WAS PREVIOUSLY
PUSHED OFF TO THE EAST. A 171106Z ASCAT METOP-B BULLSEYE CONFIRMS THE
TROPICAL CONVERSION WITH A SYMMETRICAL LLCC, BUT THE WIND FIELD REMAINS
LOPSIDED, WITH LIGHT WINDS IN THE WESTERN HALF OF THE SYSTEM, AND
EMBEDDED AREAS OF 25-30 KNOT WINDS ALONG THE EASTERN PERIPHERY, UNDER THE
FLARING CONVECTION, WHICH ARE NOT CONSIDERED TO BE REPRESENTATIVE OF THE
OVERALL INTENSITY OF THE SYSTEM. ENVIRONMENTAL ANALYSIS REVEALS AN
IMPROVEMENT IN CONDITIONS DUE TO A DECREASE IN VWS (DOWN TO 5-10 KNOTS),
AN INCREASE IN POLEWARD OUTFLOW, BUT NOT MUCH A CHANGE IN THE SSTS
DEPARTMENT (27-28C). GLOBAL MODELS ARE IN AGREEMENT THAT 91W HAS A BRIEF
WINDOW OF 6-12 HOURS TO INTENSIFY BEFORE TROUGHING OUT AND GETTING PICKED
UP BY AN APPROACHING LONGWAVE TROUGH AND TRANSITIONING ONCE AGAIN TO A
SUBTROPICAL THEN EXTRATROPICAL LOW. 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
181330Z.//
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