ABPW10 PGTW 210600
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/SIGNIFICANT TROPICAL WEATHER ADVISORY FOR THE WESTERN AND
/SOUTH PACIFIC OCEANS/210600Z-220600ZSEP2021//
RMKS/
1. WESTERN NORTH PACIFIC AREA (180 TO MALAY PENINSULA):
   A. TROPICAL CYCLONE SUMMARY: NONE.
   B. TROPICAL DISTURBANCE SUMMARY:
      (1) THE AREA OF CONVECTION (INVEST 99W) PREVIOUSLY LOCATED 
NEAR 10.3N 154.6E IS NOW LOCATED NEAR 10.3N 154.7E, APPROXIMATELY 
612 NM EAST-SOUTHEAST OF GUAM. ANIMATED MULTISPECTRAL SATELLITE 
IMAGERY (MSI) REVEALS AN ENLONGATED WAVE AXIS WITH THE LOW LEVEL 
CONVERGENCE OF SOUTHWESTERLY AND EASTERLY WINDS SUPPORTING AN AREA 
OF DEEP CONVECTION ON THE SOUTH SIDE OF THE WAVE AXIS. A 202347Z 
ASCAT-B IMAGE DEPICTS BROAD BELT OF 15-20 KT WINDS ACCOMPANIED BY 
STRONG FLARING CONVECTION IN THE SOUTHERN HALF OF THE AREA. THE 
SCATTEROMETER DATA AND ANIMATED VISIBLE IMAGERY SHOW STRONG LOW 
LEVEL CONVERGENCE ON THE EAST SIDE OF THE WAVE ENVELOPE, AND THIS IS 
THE MOST LIKELY REGION FOR DEVELOPMENT. ENVIRONMENTAL ANALYSIS 
INDICATES A FAVORABLE ENVIRONMENT FOR DEVELOPMENT WITH A COMBINATION 
OF POLEWARD AND EQUATORWARD OUTFLOW, LOW (5-10 KT) VWS AND WARM (30-
31C) SEA SURFACE TEMPERATURES. RECENT ANIMATED WATER VAPOR IMAGERY 
SEEMS TO SUPPORT THE BEGINNINGS OF AN UPPER-LEVEL ANTICYCLONE OVER 
THE SYSTEM, WHICH IS SOMETHING THE GLOBAL MODELS HAVE BEEN DEPICTING 
AS WELL, WHICH IF PROVEN OUT, WILL PROVIDE ADDITIONAL SUPPORT TO THE 
DEVELOPMENT OF THE SYSTEM. GLOBAL MODELS ARE IN AGREEMENT THAT 
INVEST 99W WILL TRACK TO THE NORTHWEST. HOWEVER, THEY ARE SPLIT ON 
THE DEGREE OF DEVELOPMENT. GFS AND ITS ENSEMBLE AND NAVGEM ARE THE 
MOST AGGRESSIVE, SHOWING DEVELOPMENT OF A TROPICAL DEPRESSION WITHIN 
THE NEXT 48 HOURS OR LESS. ECMWF AND ITS ENSEMBLE HOWEVER ARE MUCH 
MORE BEARISH, INDICATING LITTLE TO NO DEVELOPMENT WITH THIS SYSTEM. 
BASED ON THE POTENTIAL FOR ACCELERATED DEVELOPMENT TIMELINE AND 
PROXIMITY TO GUAM AND THE NORTHERN MARIANAS, THE SYSTEM IS UPGRADED 
TO MEDIUM. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 15 TO 
20 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1008 
MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL 
CYCLONE WITHIN THE NEXT 24 HOURS IS UPGRADED TO MEDIUM.
      (2) NO OTHER SUSPECT AREAS.
   C. SUBTROPICAL SYSTEM SUMMARY: NONE.
2. SOUTH PACIFIC AREA (WEST COAST OF SOUTH AMERICA TO 135 EAST):
   A. TROPICAL CYCLONE SUMMARY: NONE.
   B. TROPICAL DISTURBANCE SUMMARY: NONE.
   C. SUBTROPICAL SYSTEM SUMMARY: NONE.//
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