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Tropical Storm Greg Discussion Number   9
NWS National Hurricane Center Miami FL       EP072017
900 AM MDT Wed Jul 19 2017

Earlier microwave data indicate that the center of Greg was located
near the northwestern edge of the main convective cloud shield.
However, recent early-light visible satellite images suggest the
system is beginning to become better organized with the center
embedded beneath the cold cloud tops and increased banding over the
western portion of the circulation.  Subjective and objective Dvorak
satellite estimates range from 43 kt to 55 kt, but the initial
intensity will remain 40 kt, in deference to the overnight ASCAT
data which indicated that peak winds were lower than the Dvorak
estimates.

The shear that has been affecting the tropical cyclone during the
past couple of days appears to be decreasing.  This is expected to
allow strengthening while Greg moves over warm SSTs and through a
high moisture environment.  The intensity guidance is a bit higher
than before, with the HWRF, HCCA, and SHIPS guidance making Greg a
hurricane in 2 to 3 days.  The NHC forecast is a little more
conservative and slightly below the model consensus late in the
period due to uncertainties regarding the potential interaction
with TD Eight-E.  The global models have trended over the past 24
hours of indicating Greg will become the dominate cyclone.  If these
trends continue, additional upward adjustments to the NHC intensity
forecast may be needed.

Greg is moving westward or 270/9 kt. A mid- to upper-level ridge
extending westward from northwestern Mexico should steer the
tropical storm westward to west-northwestward during the next day or
two. After that time, Greg is forecast to accelerate westward around
the northern portion of TD Eight's circulation and continue on
that general heading late in the period as the ridge builds westward
to the north of the cyclone. Although the track guidance has come
into better agreement on this scenario, there still remains a fair
amount of uncertainty due to the potential interaction with TD
Eight. The models have trended toward a slower motion in the short
term and the NHC track has been adjusted according.  At 72 hours and
beyond, the official forecast is close to the various consensus
aides, and not too different from the previous NHC track.


FORECAST POSITIONS AND MAX WINDS

INIT  19/1500Z 14.2N 112.0W   40 KT  45 MPH
 12H  20/0000Z 14.3N 113.3W   50 KT  60 MPH
 24H  20/1200Z 14.7N 115.1W   55 KT  65 MPH
 36H  21/0000Z 15.4N 117.4W   60 KT  70 MPH
 48H  21/1200Z 15.9N 119.7W   60 KT  70 MPH
 72H  22/1200Z 16.4N 125.0W   55 KT  65 MPH
 96H  23/1200Z 15.7N 130.1W   45 KT  50 MPH
120H  24/1200Z 15.5N 135.0W   30 KT  35 MPH

$$
Forecaster Brown

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