922 
 WTPZ44 KNHC 041436
 TCDEP4
 
 HURRICANE ISELLE DISCUSSION NUMBER  17
 NWS NATIONAL HURRICANE CENTER MIAMI FL       EP092014
 800 AM PDT MON AUG 04 2014
 
 Iselle continues to intensify and has reached category 4 strength.
 Convective cloud tops as cold as -75C surround the eye, which has
 grown to a diameter of 25-30 n mi.  Dvorak estimates were a
 consensus T6.0/115 kt from TAFB and SAB at 1200 UTC, and the
 objective UW-CIMSS ADT has crept up to T6.3/122 kt since that time.
 Based on these estimates, the initial intensity is raised to 120
 kt. Vertical shear is expected to remain light for the next 24 hours
 or so while Iselle moves over gradually cooler SSTs.  Since Iselle
 has some characteristics of an annular hurricane, it is likely to
 change little in intensity during the next day or so, and even when
 it begins to weaken, the trend should be gradual.  On day 3, Iselle
 will be moving over the coldest water (between 25 and 26C) along
 its forecast track, and vertical shear is expected to increase to
 about 15-20 kt.  Both factors should induce quicker weakening at
 that time.  The NHC intensity forecast remains above all of the
 typically used intensity models during the first 24 hours, is very
 close to the consensus on days 2-3, and then more closely follows
 the decay shown by the LGEM model toward the latter part of the
 forecast period.
 
 Iselle's initial motion is 275/9 kt.  A mid- to upper-level
 shortwave trough is swinging by to the north of the hurricane and
 eroding the subtropical ridge, which should cause Iselle to slow
 down a bit during the next 24 hours.  After that time, a mid-level
 high is forecast to develop and strengthen between Hawaii and
 California, forcing Iselle to turn west-northwestward and accelerate
 as it approaches and moves near the Hawaiian Islands.  The track
 guidance has been stable and tightly clustered for a few cycles now,
 and no significant changes were required to the NHC track forecast.
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  04/1500Z 16.2N 136.5W  120 KT 140 MPH
  12H  05/0000Z 16.2N 137.7W  115 KT 135 MPH
  24H  05/1200Z 16.3N 139.2W  110 KT 125 MPH
  36H  06/0000Z 16.8N 141.4W   95 KT 110 MPH
  48H  06/1200Z 17.4N 144.2W   80 KT  90 MPH
  72H  07/1200Z 19.0N 150.5W   60 KT  70 MPH...EAST OF HAWAII
  96H  08/1200Z 21.0N 157.0W   50 KT  60 MPH...NEAR HAWAII
 120H  09/1200Z 22.5N 162.0W   45 KT  50 MPH...WEST OF HAWAII
 
 $$
 Forecaster Berg