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Tropical Storm Greg Discussion Number  10
NWS National Hurricane Center Miami FL       EP072017
300 PM MDT Wed Jul 19 2017

Deep convection associated with Greg has thinned out again this
afternoon, with the low-level center evident near the northwestern
portion of a loosely curved convective band.  Although Dvorak
satellite intensity estimates suggest maximum winds of 45 to 55 kt,
recent ASCAT data continued to support a lower intensity of around
40 kt.  The cirrus outflow and current structure of the tropical
cyclone continue to suggest that there is moderate shear over the
system which may be coming from a layer below 200 mb since the
analyzed 850 to 200 mb shear is low.  The global models predict
that there should be a better upper-level wind pattern over Greg
within the next couple of days, and as a result, strengthening is
forecast.  However, the NHC forecast remains below much of the
guidance and the intensity consensus since the shear has failed to
abate thus far. After 48 hours, the GFS and ECWMF show Greg in very
different upper-level environments with the GFS being much more
conducive than the ECMWF.  Due to this uncertainty, the NHC forecast
again is below the intensity consensus at 72 hours and beyond, and
it is a low confidence forecast.

Greg is moving westward at about 9 kt. There has been no
significant change to the track forecast reasoning.  Greg is
forecast to move west-northwestward during the next couple of days
to the south of a mid- to upper-level ridge that extends westward
from northern Mexico.  Greg should turn westward and accelerate
around the northern portion of TD Eight-E's circulation in a few
days.  The dynamical model guidance is in good agreement on this
overall scenario, but there are large along-track or speed
differences with the GFS being much slower than the ECMWF.  Overall,
the track guidance has again trended slower so the NHC forecast has
been adjusted accordingly.


FORECAST POSITIONS AND MAX WINDS

INIT  19/2100Z 14.3N 112.7W   40 KT  45 MPH
 12H  20/0600Z 14.4N 113.9W   45 KT  50 MPH
 24H  20/1800Z 14.9N 115.9W   50 KT  60 MPH
 36H  21/0600Z 15.5N 118.2W   55 KT  65 MPH
 48H  21/1800Z 16.0N 120.5W   60 KT  70 MPH
 72H  22/1800Z 16.2N 125.5W   60 KT  70 MPH
 96H  23/1800Z 16.0N 130.5W   50 KT  60 MPH
120H  24/1800Z 16.0N 135.0W   40 KT  45 MPH

$$
Forecaster Brown

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