733 
 WTPZ44 KNHC 010258
 TCDEP4
 
 HURRICANE GUILLERMO DISCUSSION NUMBER   9
 NWS NATIONAL HURRICANE CENTER MIAMI FL       EP092015
 800 PM PDT FRI JUL 31 2015
 
 Both microwave and conventional satellite imagery indicate that
 Guillermo has not become any better organized during the past
 several hours. In fact, the satellite presentation appears to have
 deteriorated since earlier today with microwave data showing the
 northwestern portion of the eyewall eroding.  Satellite intensity
 estimates from TAFB and SAB and the latest objective intensity
 estimate from UW-CIMSS ADT suggest that initial intensity remains 90
 kt.
 
 Guillermo continues to move rapidly to the west-northwest, with an
 initial motion estimate of 285/18 kt. Little change to this motion
 is expected for the next 24 hours, with the cyclone remaining to the
 south of a mid-level subtropical ridge. Beyond 24 hours to around
 72 hours, a deepening mid- to upper-level trough over the central
 Pacific is forecast to create a break in the subtropical ridge,
 which should cause the tropical cyclone to slow down and turn more
 toward the northwest. The spread in the guidance suite increases
 beyond 72 hours, but most of the models maintain a general
 west-northwestward motion.  The new forecast track is basically an
 update of the previous track through 72 hours, and is then nudged
 slightly to the right or north of the previous track toward the
 multi-model consensus thereafter.
 
 The intensity forecast has become somewhat problematic. The reason
 for the recent arrested development is unclear, although it might be
 related to dry air entrainment into the northwestern quadrant of the
 cyclone. However, there is still the opportunity for Guillermo to
 strengthen a bit more during the next 12 to 24 hours, while the
 system remains within a low-shear environment and over warm sea
 surface temperatures. The new intensity forecast is adjusted
 slightly downward to 95 kt at the 12- and 24-hour forecast times.
 Thereafter, the cyclone is forecast to move into an upper-level
 deformation zone between subtropical ridges to the east and west,
 which is a less favorable environment.  Also, sea surface
 temperatures gradually cool along the forecast track. We have
 followed the previous forecast trend of gradual weakening, which is
 in good agreement with the latest SHIPS/LGEM and IVCN consensus
 guidance. When Guillermo approaches the Hawaiian Islands, it is
 expected to encounter increasing westerly shear, and the new
 intensity forecast follows the previous forecast in weakening
 Guillermo to tropical storm strength.
 
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  01/0300Z 13.2N 136.1W   90 KT 105 MPH
  12H  01/1200Z 13.7N 138.5W   95 KT 110 MPH
  24H  02/0000Z 14.3N 141.1W   95 KT 110 MPH
  36H  02/1200Z 15.0N 143.2W   90 KT 105 MPH
  48H  03/0000Z 15.8N 145.0W   80 KT  90 MPH
  72H  04/0000Z 17.0N 147.5W   65 KT  75 MPH
  96H  05/0000Z 19.0N 150.5W   60 KT  70 MPH
 120H  06/0000Z 20.5N 153.5W   50 KT  60 MPH
 
 $$
 Forecaster Beven/Jacobson