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TROPICAL STORM DARBY DISCUSSION NUMBER  34
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP052016
800 PM PDT TUE JUL 19 2016

Darby continues to maintain deep convection near its center, and in
fact the convective cloud tops have cooled a bit over the past
several hours.  The current intensity estimate, 55 kt, is unchanged
from the past advisory and is consistent with the latest Dvorak
estimate from TAFB.  The storm should encounter modestly increasing
vertical shear and drier air over the next several days, but will be
moving over slightly warmer waters.  These factors should result in
only a slow rate of weakening over the forecast period, and this is
reflected in the official intensity forecast, which is near the
model consensus and above the latest SHIPS and LGEM guidance.  It
is worth noting however, that longer-range intensity prediction has
little skill.

Based on geostationary and microwave fixes, the westward motion,
280/11 kt, continues.  The track forecast reasoning has not
changed.  A mid-level subtropical ridge extending westward from the
southern Great Plains should continue to steer Darby on a westward
or slightly south-of-westward heading for the next few days.  In the
latter part of the forecast period, a mid-level cyclone to the north
of the Hawaiian Islands should cause Darby to turn toward the
northwest.  The official forecast is very close to the multi-model
consensus.  However, the GFS and ECMWF ensemble tracks show
considerable spread on days 3-5, indicating a significant amount of
uncertainty in the forecast track late in the period.

FORECAST POSITIONS AND MAX WINDS

INIT  20/0300Z 20.0N 137.8W   55 KT  65 MPH
 12H  20/1200Z 20.0N 139.5W   50 KT  60 MPH
 24H  21/0000Z 19.8N 141.8W   50 KT  60 MPH
 36H  21/1200Z 19.5N 144.1W   50 KT  60 MPH
 48H  22/0000Z 19.2N 146.3W   45 KT  50 MPH
 72H  23/0000Z 19.1N 150.2W   45 KT  50 MPH
 96H  24/0000Z 20.2N 152.2W   45 KT  50 MPH
120H  25/0000Z 22.0N 154.0W   40 KT  45 MPH

$$
Forecaster Pasch

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