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Tropical Storm GREG Forecast Discussion


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000
WTPZ42 KNHC 231433
TCDEP2

Tropical Storm Greg Discussion Number  25
NWS National Hurricane Center Miami FL       EP072017
800 AM PDT Sun Jul 23 2017

Greg's convective pattern is looking a little better this morning,
with two distinct bursts of thunderstorm activity located near and
to the west of the center.  The latest Dvorak intensity estimates
range from T2.0 to T3.0, and the initial intensity will remain 45
kt since the cyclone's structure has improved somewhat during the
past several hours.

Vertical shear over Greg is less than 10 kt at the moment, but the
cyclone's biggest challenge is dry air in the surrounding
environment.  GOES-16 lower-level water vapor imagery shows that
Greg is running into a very dry low- to mid-level air mass to its
west, and this environment will likely curtail strengthening.  Greg
is forecast to maintain its intensity for another 24 hours,
followed by gradual weakening due to the dry air, increasing shear,
and cooler sea surface temperatures after 48 hours.  This scenario
is captured by all of the intensity guidance, and Greg is likely to
degenerate into a remnant low by 96 hours.

A little more southward adjustment of the center location was needed
based on additional ASCAT and other microwave data received since
the last advisory.  Still, low- to mid-level ridging to the north
of Greg is expected to maintain a westward motion through 36 hours.
The ridge is forecast to weaken after 36 hours, which should allow
the cyclone to gain a little more latitude on days 2 through 4.
The low-level trade winds are then expected to push the remnant low
west-southwestward by day 5.  Except for a southward adjustment in
the track forecast to account for the initial position, the model
guidance is in good agreement, and no other significant changes
were required from the previous advisory.

FORECAST POSITIONS AND MAX WINDS

INIT  23/1500Z 14.3N 129.0W   45 KT  50 MPH
 12H  24/0000Z 14.3N 130.7W   45 KT  50 MPH
 24H  24/1200Z 14.5N 133.0W   45 KT  50 MPH
 36H  25/0000Z 14.7N 134.8W   40 KT  45 MPH
 48H  25/1200Z 15.0N 136.2W   35 KT  40 MPH
 72H  26/1200Z 16.1N 138.6W   30 KT  35 MPH
 96H  27/1200Z 16.5N 141.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  28/1200Z 15.9N 143.6W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Berg