ZCZC MIATCDEP5 ALL
TTAA00 KNHC DDHHMM

TROPICAL STORM DARBY DISCUSSION NUMBER  35
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP052016
200 AM PDT WED JUL 20 2016

Darby has changed little in structure during the past few hours.
Deep convection with cloud tops as cold as -60C continue near the
center, and recent microwave images showed a nearly closed
mid-level ring.  Dvorak Current Intensity numbers remain 3.5 from
TAFB and SAB, and the initial intensity is therefore held at 55 kt.
Darby is over SSTs around 25C and is heading toward warmer waters.
However, vertical shear is expected to increase in the next 24-36
hours.  Interestingly, the intensity models aren't in agreement on
what will happen with Darby's intensity during this period.  While
the SHIPS and LGEM models indicate steady weakening over the next
few days, the HWRF and Florida State Superensemble actually show
some re-intensification in 24-36 hours.  Due to these competing
signals, the NHC official forecast shows little change in intensity
during the next 48 hours, followed by gradual weakening on days
3-5.  This updated forecast is not too different from the previous
one, except that it delays steady weakening until after 48 hours.

Darby is moving westward with an initial motion of 270/11 kt.  The
cyclone is located to the south of the subtropical ridge, which
should maintain a westward motion for the next three days.  After
that time, a retrograding mid- to upper-level low north of the
Hawaiian Islands will create a break in the ridge, causing Darby to
turn northwestward and north-northwestward on days 4 and 5.  With
the exception of the GFDL, there is very little cross-track spread
among the model guidance.  However, there are some noticeable speed
differences, with the ECMWF and UKMET showing more acceleration
after the turn compared to the GFS and HWRF models.  For now, the
NHC official forecast, which is very similar to the previous
forecast, splits the difference and is near a consensus of the GFS
and ECMWF models.

FORECAST POSITIONS AND MAX WINDS

INIT  20/0900Z 20.0N 138.9W   55 KT  65 MPH
 12H  20/1800Z 19.8N 140.6W   50 KT  60 MPH
 24H  21/0600Z 19.5N 142.9W   50 KT  60 MPH
 36H  21/1800Z 19.2N 145.2W   50 KT  60 MPH
 48H  22/0600Z 18.9N 147.5W   50 KT  60 MPH
 72H  23/0600Z 19.0N 151.0W   45 KT  50 MPH
 96H  24/0600Z 20.0N 152.5W   45 KT  50 MPH
120H  25/0600Z 23.0N 154.0W   40 KT  45 MPH

$$
Forecaster Berg

NNNN