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Tropical Storm Greg Discussion Number   4
NWS National Hurricane Center Miami FL       EP072017
300 AM MDT Tue Jul 18 2017

Deep convection has increased in both intensity and coverage during
the last several hours over and to the southeast of the center of
the cyclone.  The Dvorak classifications from TAFB and SAB at 0600
UTC were 2.0/30 kt, but ADT values and satellite consensus estimates
from CIMSS at the University of Wisconsin suggest a slightly higher
intensity.  Based on the improvement in convective organization
during the past few hours, the initial intensity is increased to 35
kt, making the system Tropical Storm Greg.

The northwesterly shear currently affecting Greg is expected to
gradually lessen, and the upper-level wind pattern will likely
become favorable in the 24- to 60-h time frame.  Therefore, the NHC
intensity forecast continues to show modest strengthening during the
next couple of days.  After that time, however, the shear is
expected to increase out of the south or southwest as the cyclone
approaches an upper-level low. This increase in shear combined with
drier air and cooler waters should end the strengthening trend and
cause weakening.  The depression will likely degenerate to a remnant
low in 4 to 5 days when it moves over SSTs below 26 deg C.  The NHC
intensity forecast is the same as the previous one, and is in line
with the bulk of the guidance.

Greg is moving west-northwestward at 8 kt to the south of a low- to
mid-level ridge.  A westward to west-northwestward motion with some
increase in forward speed is expected during the next few days as
the ridge strengthens a little.  Some of the models show Greg
interacting with the disturbance currently located about 700 n mi
to its west in 4 to 5 days, which could cause the cyclone to turn
south of due west at that time.  The track models are in general
agreement, and the NHC forecast lies closest to the consensus aids.

FORECAST POSITIONS AND MAX WINDS

INIT  18/0900Z 14.6N 107.6W   35 KT  40 MPH
 12H  18/1800Z 14.7N 108.7W   35 KT  40 MPH
 24H  19/0600Z 15.0N 110.6W   40 KT  45 MPH
 36H  19/1800Z 15.4N 112.6W   40 KT  45 MPH
 48H  20/0600Z 15.8N 114.7W   40 KT  45 MPH
 72H  21/0600Z 16.9N 119.7W   35 KT  40 MPH
 96H  22/0600Z 17.1N 124.6W   30 KT  35 MPH
120H  23/0600Z 16.5N 129.5W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Cangialosi

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