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Tropical Storm Greg Forecast Discussion


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000
WTPZ42 KNHC 230851
TCDEP2

Tropical Storm Greg Discussion Number  24
NWS National Hurricane Center Miami FL       EP072017
200 AM PDT Sun Jul 23 2017

The center of Greg has been difficult to locate tonight, but earlier
microwave data and an ASCAT pass that just barely caught the center
indicate that the tropical storm remains sheared.  At the time of
those passes, the center was located just southeast of the main
convective mass and there is no reason to believe that has changed.
Although the ASCAT pass missed the western portion of the
circulation, it still showed winds of 38 kt in the northeast
quadrant.  Assuming the winds are a little higher within the
convection, the initial intensity has been held at 45 kt.

Although Greg is moving away from an upper-level low and the worst
of the vertical shear, the near-storm environment is still fairly
dry, as diagnosed in the GFS and ECMWF-based SHIPS.  This should
be enough to prevent the cyclone from strengthening, and very
gradual weakening is supported by most of the guidance.  After
about 48 hours, cooler SSTs and increasing shear should result in
additional weakening, and Greg is forecast to become a remnant low
by day 4.  The new intensity forecast is very similar to the
previous advisory.

The aforementioned ASCAT pass suggested that the center of Greg is a
little farther south than previously estimated, and the track
forecast has been adjusted accordingly.  Aside from that, little
change has been made and the official forecast is near the middle
of the tightly clustered guidance.  All of the global models still
show Greg moving along the southern periphery of a low- to mid-level
ridge for the next couple of days, followed by a turn toward the
northwest as the ridge weakens slightly.  By the end of the
forecast period a turn back to the west as a remnant low is
expected, when Greg becomes steered primarily by low-level trade
winds.


FORECAST POSITIONS AND MAX WINDS

INIT  23/0900Z 14.7N 127.7W   45 KT  50 MPH
 12H  23/1800Z 14.6N 129.5W   45 KT  50 MPH
 24H  24/0600Z 14.6N 131.9W   40 KT  45 MPH
 36H  24/1800Z 14.8N 133.9W   40 KT  45 MPH
 48H  25/0600Z 15.2N 135.5W   35 KT  40 MPH
 72H  26/0600Z 16.1N 138.0W   30 KT  35 MPH
 96H  27/0600Z 16.9N 140.4W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  28/0600Z 17.0N 143.5W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Zelinsky