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Tropical Storm Greg Discussion Number  11
NWS National Hurricane Center Miami FL       EP072017
900 PM MDT Wed Jul 19 2017

Greg's convective pattern has not improved this evening, with most
of the associated shower and thunderstorm activity concentrated to
the south and west of the center.  Since subjective and objective
Dvorak estimates have either remained steady or fallen from six
hours ago, the initial intensity is held at 40 kt based on the
earlier ASCAT passes.

Greg's initial motion is westward, or 270/9 kt.  A strong mid- to
upper-level ridge axis extending westward from northern Mexico
should cause Greg to move westward or west-northwestward for the
entire forecast period, but at a slightly faster forward speed
beginning in about 24 hours.  The biggest forecast challenge for
Greg's track is its forward speed, since there is a notable
difference between the faster ECMWF and the slower GFS and HWRF
models.  Longitude-wise, the updated NHC forecast is close to the
TVCN multi-model consensus.  However, a slight shift in the overall
guidance envelope required a bit of a southward nudge compared to
the previous forecast.

It's not exactly clear why Greg's convection has not become any
better organized since the analyzed deep-layer shear is less than 10
kt.  However, products from UW-CIMSS do suggest that there is 15-20
kt of mid-level shear extending northeast of Greg's center, which
could be disrupting the convection in that quadrant.  Assuming that
the ambient environment slowly improves over time, Greg should be
able to eventually become better organized and strengthen as
indicated by most of the intensity models.  The updated NHC
forecast has been bumped up slightly at 24 hours and beyond to be
a little closer to the intensity consensus.  However, this new
forecast is still 10-15 kt below the usually reliable models like
HWRF, HCCA, and Florida State Superensemble, just in case Greg
continues to struggle in becoming better organized.

FORECAST POSITIONS AND MAX WINDS

INIT  20/0300Z 14.1N 113.6W   40 KT  45 MPH
 12H  20/1200Z 14.3N 115.0W   45 KT  50 MPH
 24H  21/0000Z 14.8N 117.1W   55 KT  65 MPH
 36H  21/1200Z 15.2N 119.3W   60 KT  70 MPH
 48H  22/0000Z 15.6N 121.7W   65 KT  75 MPH
 72H  23/0000Z 15.7N 126.8W   65 KT  75 MPH
 96H  24/0000Z 15.3N 131.6W   55 KT  65 MPH
120H  25/0000Z 15.5N 135.5W   45 KT  50 MPH

$$
Forecaster Berg

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