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Tropical Depression GREG Forecast Discussion


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Tropical Depression Greg Discussion Number  34
NWS National Hurricane Center Miami FL       EP072017
200 PM PDT Tue Jul 25 2017

Greg is only producing patchy deep convection, and its center is
becoming increasingly difficult to locate.  Subjective and
objective Dvorak CI numbers have all fallen below 2.5, and Greg is
therefore downgraded to a 30-kt depression.  Southerly shear
continues to increase over the cyclone due to a sharp upper-level
shear axis located to its southwest, and that shear is expected to
increase further and turn out of the northwest during the next 48
hours.  In addition, Greg is moving into a drier, more stable air
mass, and over increasingly cooler waters.  Therefore, continued
weakening is expected, and Greg could also end up losing all
organized deep convection by 36 hours.  The NHC forecast calls for
Greg to degenerate into a remnant low at that time, but it could
certainly occur sooner.  The remnant low is likely to open up into
a trough by day 5.

Greg is moving west-northwestward, or 295/10 kt.  Low- to mid-level
troughing north of the depression should maintain a northwestward
or west-northwestward motion for the next 24 hours.  After that
time, the remnant low should turn westward and then west-
southwestward, steered by the low-level trade winds.  The spread in
the track models continues to be speed related (bounded by the
slower GFS and faster ECMWF), and the NHC track forecast lies close
to the various consensus models.  This updated forecast is a little
faster than the previous one.

FORECAST POSITIONS AND MAX WINDS

INIT  25/2100Z 16.2N 137.9W   30 KT  35 MPH
 12H  26/0600Z 16.9N 138.9W   30 KT  35 MPH
 24H  26/1800Z 17.6N 140.4W   30 KT  35 MPH
 36H  27/0600Z 17.8N 142.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  27/1800Z 17.7N 143.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  28/1800Z 16.9N 146.6W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  29/1800Z 16.0N 149.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  30/1800Z...DISSIPATED

$$
Forecaster Berg

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