WTPS21 PGTW 272130
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE FORMATION ALERT (INVEST 91P)//
RMKS/
1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN
120 NM EITHER SIDE OF A LINE FROM 14.7S 170.6E TO 16.8S 174.1E
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 28 TO 33 KNOTS. METSAT
IMAGERY AT 271800Z INDICATES THAT A CIRCULATION CENTER IS LOCATED
NEAR 14.7S 170.9E. THE SYSTEM IS MOVING EAST-SOUTHEASTWARD AT 08
KNOTS.
2. REMARKS: THE AREA OF CONVECTION (INVEST 91P) HAS PERSISTED NEAR 
14.7S 170.9E, APPROXIMATELY 233 NM NORTHEAST OF PORT VILA. ANIMATED 
HIMAWARI-9 INFRARED SATELLITE IMAGERY INDICATES A COMPACT BUT WELL-
FORMED AREA OF DEEP CONVECTION EMBEDDED WITHIN THE SOUTH PACIFIC 
CONVERGENCE ZONE (SPCZ) HAS BEEN RAPIDLY DEVELOPING OVERNIGHT. THE 
FIRST FEW FRAMES OF DAYLIGHT IN THE VISIBLE CHANNEL REVEALS PULSATING 
OVERSHOOTING CLOUD TOPS NEAR THE CENTER OF THE CENTRAL DENSE OVERCAST, 
WITH FORMATIVE BANDING STRUCTURES TRYING TO BECOME ESTABLISHED.  THE 
CURRENT INTENSITY IS ASSESSED TO BE 30 KTS BASED ON THE LIMITED DATA 
AVAILABLE, INCLUDING A 271800Z PGTW DVORAK ANALYSIS WHICH YIELDED A 
T2.5 (35 KTS). AN INITIAL 271800Z T1.5 KNES FIX ESTABLISHED AN 
INITIAL INTENSITY OF 25 KTS FROM THAT AGENCY. A PGTW REANALYSIS OF 
271200Z IMAGERY YIELDED A T2.0 (30 KTS). UNFORTUNATELY, THERE IS NO 
CURRENT SCATTEROMETRY OR OTHER OCEAN SURFACE WIND DATA TO CORROBORATE 
THE LIMITED DVORAK ESTIMATES. 91P IS CURRENTLY IN A NARROW CHANNEL OF 
FAVORABLE ENVIRONMENTAL CONDITIONS CHARACTERIZED BY LOW VWS (05-10KT), 
GOOD DIVERGENT POLEWARD OUTFLOW, MOIST MID-LEVEL RELATIVE HUMIDITY, 
AND WARM SST (29-30C). NUMERICAL GUIDANCE DOES NOT CALL FOR TROPICAL 
CYCLONE FORMATION, HOWEVER THE AVAILABLE 12Z GLOBAL MODELS ARE NOT 
HANDLING THE CURRENT ANALYSIS WELL, WHICH IS OFTEN TYPICAL OF SYSTEMS 
WITHIN THE SPCZ. THAT SAID, IT IS POSSIBLE INVEST 91P MAY HAVE ALREADY 
REACHED ITS PEAK AND HAS ONLY A LIMITED WINDOW FOR ADDITIONAL 
DEVELOPMENT AS IT TRACKS SOUTHEASTWARD, DUE TO DRIER AIR THAT SHOULD 
BEGIN TO ENCROACH OVER THE NEXT 24 TO 36 HOURS. MAXIMUM SUSTAINED 
SURFACE WINDS ARE ESTIMATED AT 28 TO 33 KNOTS. MINIMUM SEA LEVEL 
PRESSURE IS ESTIMATED TO BE NEAR 1004 MB. 
MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 28 TO 33 KNOTS.
MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 998 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 
282130Z.
//
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