ZCZC MIATCDEP5 ALL
TTAA00 KNHC DDHHMM

TROPICAL STORM DARBY DISCUSSION NUMBER  33
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP052016
200 PM PDT TUE JUL 19 2016

Although Darby continues to exhibit a well-defined circulation, deep
convection, in the form of ragged bands, continues to gradually
diminish in coverage.  The initial intensity is subsequently lowered
to 55 kt and reflects the Dvorak intensity estimates from both TAFB
and SAB.  The cyclone is forecast to move over marginal SSTs and
into a drier, more stable air mass with increasing modest
southwesterly shear during the next several days.  The official
forecast indicates slight weakening during the next day or so, with
very little change in strength through 96 hours as Darby traverses
a slightly warmer ocean.  Thereafter, Darby is expected to again
weaken as it gains latitude and moves into a region of strong
southwesterly shear.  The official forecast is weighed heavily on
the IVCN consensus and lies above the LGEM and Decay SHIPS.  It
should be noted that longer-range, i.e. day 4 and 5, intensity
predictions have little skill.

A series of microwave images reveal an apparent northward
tilt with height of the cyclone.  Consequently, the conventional
satellite position estimates have been consistently a little north
of the microwave fixes.  Using a blend of these fixes, the initial
motion is estimated at 280/11 kt.  The synoptic reasoning for the
track forecast has not changed, as Darby will be steered generally
westward during the next 4 days.  Through the remaining portion of
the forecast, the cyclone is expected to decrease its forward speed
and gradually begin to recurve northwestward into a growing weakness
caused by an amplifying mid- to upper-level trough north of the
Hawaiian Islands.  The ECMWF global model has shifted farther south
than the previous runs.  This shift has also nudged the multi-model
consensus south as well, and the official forecast follows suit and
is close the GFS and ECMWF ensemble mean guidance.

FORECAST POSITIONS AND MAX WINDS

INIT  19/2100Z 19.9N 136.6W   55 KT  65 MPH
 12H  20/0600Z 20.0N 138.3W   50 KT  60 MPH
 24H  20/1800Z 20.0N 140.6W   45 KT  50 MPH
 36H  21/0600Z 19.7N 142.8W   45 KT  50 MPH
 48H  21/1800Z 19.4N 145.1W   45 KT  50 MPH
 72H  22/1800Z 19.2N 149.3W   45 KT  50 MPH
 96H  23/1800Z 19.9N 152.0W   45 KT  50 MPH
120H  24/1800Z 21.6N 153.7W   40 KT  45 MPH

$$
Forecaster Roberts

NNNN