WTPA44 PHFO 180931
TCDCP4

TROPICAL STORM GUILLERMO DISCUSSION NUMBER  25
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI   EP102009
1100 PM HST MON AUG 17 2009

A TIMELY QUIKSCAT PASS SHOWED THAT GUILLERMO REMAINS A TROPICAL
STORM. THE WIND FIELD IS HIGHLY ASYMMETRIC...WITH TROPICAL STORM
FORCE WINDS EXTENDING OVER 200 NM TO THE NORTH BUT NO TROPICAL
STORM FORCE WINDS SOUTH OF THE CENTER. WE HAVE MODIFIED THE INITIAL
INFORMATION TO ACCOUNT FOR THE QUICKSCAT INFORMATION AND HAVE ALSO
MODIFIED THE FORECAST TRACK AND INTENSITY.

THE TRACK GUIDANCE REMAINS CLOSELY GROUPED AND I HAVE KEPT THE
FORECAST TRACK NEAR THE CONSENSUS. GUILLERMO IS FORECAST TO
CONTINUE MOVING NORTHWEST FOR THE NEXT 36 HOURS...ALONG THE SOUTH
EDGE OF A SURFACE HIGH FAR TO THE NORTH-NORTHEAST. AFTER 36 HOURS
GUILLERMO WILL CURVE TO THE WEST...THEN SLIGHTLY SOUTH OF WEST...AS
A NEW HIGH FAR NORTH-NORTHWEST OF THE CYCLONE PUSHES SOUTH.

GUILLERMO HAS A VERY WEAK CLOUD SIGNATURE WITH AN EXPOSED LOW LEVEL
CIRCULATION CENTER AND CONVECTION SHEARED WELL TO THE NORTH.
DESPITE THIS...SCATTEROMETER DATA SHOWED TROPICAL STORM FORCE WINDS
EXTENDING FAR NORTH OF THE CENTER. THE MAIN REASON FOR THE STRONGER
THAN EXPECTED WINDS IS A TIGHT PRESSURE GRADIENT BETWEEN THE
CYCLONE AND A STRONG HIGH TO THE NORTH-NORTHEAST. SINCE THIS TIGHT
GRADIENT WILL CONTINUE...WE HAVE MODIFIED THE INTENSITY FORECAST TO
KEEP GUILLERMO AT ITS CURRENT STRENGTH THROUGH 36 HOURS. THE WIND
FIELD WILL REMAIN ASYMMETRIC...WITH TROPICAL STORM FORCE WINDS ONLY
NORTH OF THE CENTER. GUILLERMO WILL THEN GRADUALLY WEAKEN AS IT
TRACKS FARTHER WEST.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      18/0900Z 23.9N 148.9W    40 KT
 12HR VT     18/1800Z 25.4N 151.2W    40 KT
 24HR VT     19/0600Z 27.3N 154.7W    40 KT
 36HR VT     19/1800Z 28.7N 158.3W    40 KT
 48HR VT     20/0600Z 29.7N 162.1W    35 KT
 72HR VT     21/0600Z 29.8N 168.1W    30 KT
 96HR VT     22/0600Z 28.7N 174.9W    30 KT...DISSIPATING
120HR VT     23/0600Z 28.0N 178.6E    25 KT...DISSIPATING
 
$$
FORECASTER DONALDSON