970 
 WTPZ44 KNHC 011434
 TCDEP4
 
 TROPICAL STORM ISELLE DISCUSSION NUMBER   4
 NWS NATIONAL HURRICANE CENTER MIAMI FL       EP092014
 800 AM PDT FRI AUG 01 2014
 
 Recent microwave data indicate that Iselle has a well-defined
 structure with a nearly closed ring of deep convection around the
 center.  In infrared satellite imagery, hints of a possible ragged
 eye have been noted although the convection is a little thin on the
 western side.  Dvorak intensity estimates are T2.5/35 kt from SAB,
 T3.5/55 kt from TAFB, and T3.9/63 kt from the UW-CIMSS ADT.  The
 initial intensity is raised to 55 kt based on a blend of these data.
 
 The subtropical ridge continues to propel Iselle west-northwestward
 with an estimated motion of 295/9 kt.  This motion is expected to
 continue for the next 48 hours.  By day 3, however, a mid- to upper-
 level trough is forecast to amplify off the California coast while a
 fairly strong mid-level high becomes established just to the
 northeast of Hawaii.  This pattern should cause Iselle to move more
 slowly toward the west between days 3 through 5.  The track
 guidance is in good agreement for the first 2 days of the forecast
 but then diverges a bit thereafter, with the GFS and HWRF taking
 Iselle on a more northern trajectory and the ECMWF and GFDL staying
 farther to the south.  The NHC official track forecast is largely
 unchanged from the previous advisory and remains near the
 multi-model consensus TVCE.
 
 UW-CIMSS shear analyses indicate that about 10 kt of northerly
 shear is affecting Iselle, which could be contributing to the thin
 convection on the western side.  The shear is expected to change
 little for the next 24 hours but should then decrease thereafter.
 The thermodynamic environment will become a little more marginal in
 2-3 days when Iselle approaches the 26C sea surface temperature
 isotherm and slightly more stable air.  Therefore, Iselle is likely
 to peak in intensity in the next 36-48 hours and then gradually
 weaken on days 3-5.  The intensity models have come into much better
 agreement compared to yesterday, and no significant changes were
 required to the official intensity forecast.
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  01/1500Z 14.1N 125.7W   55 KT  65 MPH
  12H  02/0000Z 14.6N 126.9W   65 KT  75 MPH
  24H  02/1200Z 15.1N 128.6W   70 KT  80 MPH
  36H  03/0000Z 15.5N 130.4W   75 KT  85 MPH
  48H  03/1200Z 15.9N 132.2W   75 KT  85 MPH
  72H  04/1200Z 16.5N 135.5W   70 KT  80 MPH
  96H  05/1200Z 16.5N 138.0W   60 KT  70 MPH
 120H  06/1200Z 17.0N 141.5W   50 KT  60 MPH
 
 $$
 Forecaster Berg