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Tropical Storm Greg Discussion Number   8
NWS National Hurricane Center Miami FL       EP072017
300 AM MDT Wed Jul 19 2017

The increased convective organization of Greg proved to be
short-lived.  Although the SHIPS-analyzed shear remains low, the
cloud pattern now resembles that of a sheared tropical cyclone.  A
0458 UTC ASCAT-B overpass caught the eastern half of the
circulation, showing no winds above 30 kt, while  Dvorak-based
estimates of the current intensity range from 45 to 57 kt.  The
initial intensity has only been lowered to 40 kt since the ASCAT
pass missed the western half of the circulation, but this could be
generous.

Based on the aforementioned ASCAT pass, the analyzed center of the
tropical storm has been shifted farther south, and the overall
track forecast nudged southward accordingly.  While the reasoning
behind the forecast is unchanged, the model spread is still fairly
high, and run-to-run consistency is low.  For instance, the 120-h
forecast points from the 18Z and 00Z GFS model differ by nearly 300
nmi. The CMC, ECMWF, GFS, and UKMET global models still show Greg
and TD Eight-E interacting to various degrees, with each cyclone
beginning to affect the others track in about 36 hours.  This
interaction should ultimately cause Greg to accelerate toward the
west-northwest.  After about 72 hours it is still assumed that Greg
will be the dominant cyclone, so only a slight turn back toward the
west-southwest is forecast. If TD Eight-E instead becomes dominant,
then a more pronounced southern turn would be expected.

Although the initial intensity is a little lower than the previous
advisory, most of the guidance still suggests that Greg will
gradually strengthen within a warm-SST, high-moisture, low-shear
environment for the next 24-36 hours. Thus little change has been
made to the intensity forecast, which remains near the IVCN and HCCA
consensus aids.  If TD Eight-E becomes the dominant cyclone, an
alternate scenario is that Greg will dissipate much sooner than
currently forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  19/0900Z 14.3N 111.0W   40 KT  45 MPH
 12H  19/1800Z 14.4N 112.4W   45 KT  50 MPH
 24H  20/0600Z 14.8N 114.3W   50 KT  60 MPH
 36H  20/1800Z 15.4N 116.4W   55 KT  65 MPH
 48H  21/0600Z 16.0N 118.9W   55 KT  65 MPH
 72H  22/0600Z 16.9N 124.0W   40 KT  45 MPH
 96H  23/0600Z 15.8N 129.1W   30 KT  35 MPH
120H  24/0600Z 15.0N 134.0W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Zelinsky

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