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Tropical Storm Greg Forecast Discussion


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000
WTPZ42 KNHC 202033
TCDEP2

Tropical Storm Greg Discussion Number  14
NWS National Hurricane Center Miami FL       EP072017
200 PM PDT Thu Jul 20 2017

The structure of Greg has not changed much during the past few
hours, consisting of a large curved band feature with the center
located on the inside edge of the banding feature.  The satellite
intensity estimates are the same as 6 hours ago, so the initial wind
speed estimate remains 45 kt.

Greg appears to be in a conducive environment for intensification
for the next couple of days with warm water, low shear, and a moist
mid-level atmosphere.  While a mid/upper-level trough to the
northwest could influence the storm, it is forecast to remain far
enough away to not cause any significant shear.  Thus, the intensity
forecast is raised slightly from the previous advisory, but remains
near or below the intensity consensus since there is still some
uncertainty about how the remnants of TD Eight-E affect the storm.
Gradual weakening should begin in about 3 days due to the cyclone
moving over cooler waters.

The initial motion estimate is 275/9.  A westward to west-
northwestward motion is forecast for the next several days while
Greg is steered by a ridge to the north.  Model guidance is
generally in good agreement through about 72 hours, but then the
model spread grows beyond that time, depending on the respective
model's ridge strength in the western portion of the eastern Pacific
and the latitude of Greg.  The differences in the model fields are
rather subtle, so it seems best to just stay close to the model
consensus at this time.  The consensus aids haven't changed much in
the past 6 hours, and the latest NHC track forecast is basically
just an update of the previous one.

FORECAST POSITIONS AND MAX WINDS

INIT  20/2100Z 14.2N 116.4W   45 KT  50 MPH
 12H  21/0600Z 14.4N 117.8W   50 KT  60 MPH
 24H  21/1800Z 14.9N 119.9W   60 KT  70 MPH
 36H  22/0600Z 15.4N 122.0W   65 KT  75 MPH
 48H  22/1800Z 15.8N 124.3W   70 KT  80 MPH
 72H  23/1800Z 16.0N 129.0W   65 KT  75 MPH
 96H  24/1800Z 16.3N 132.9W   55 KT  65 MPH
120H  25/1800Z 17.0N 136.0W   50 KT  60 MPH

$$
Forecaster Blake