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Tropical Storm Greg Forecast Discussion


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000
WTPZ42 KNHC 222037
TCDEP2

Tropical Storm Greg Discussion Number  22
NWS National Hurricane Center Miami FL       EP072017
200 PM PDT Sat Jul 22 2017

Similar to the past few days, deep convection from the morning
hours has weakened, with the center of Greg peeking out of the
cirrus canopy on the southern side of the central dense overcast.
Although the latest satellite estimates have risen a bit, the
initial wind speed will remain 45 kt after considering the recent
degradation of the cloud pattern.

It seems like dry air has been getting into the central core of
Greg, with some outflow boundaries present in the southern
semicircle.  This dry air presents a problem for future
intensification, since it would take some time to mix out of
the storm's circulation and additional environmental dry and
stable air is in the forecast path.  Thus, the window for
strengthening may have ended, and it is becoming more likely that
Greg will just slowly weaken as environmental conditions gradually
deteriorate.  None of the historically reliable guidance strengthen
the cyclone now, and the NHC forecast is decreased from the previous
one, consistent with the latest model consensus guidance.

Greg continues moving westward or 270/11 kt.  A mid-level ridge to
the north of the tropical cyclone is likely to maintain the westward
motion for the next couple of days.  In 3-5 days, the ridge is
predicted to weaken somewhat, and this should result in Greg slowing
down and turning west-northwestward.  The GFS-based guidance has
made a large westward shift toward the ECMWF/UKMET on this cycle,
similar to its overnight trend.  Thus, the NHC forecast is shifted
westward as well and remains near or west of the model consensus at
long range.



FORECAST POSITIONS AND MAX WINDS

INIT  22/2100Z 15.1N 125.2W   45 KT  50 MPH
 12H  23/0600Z 15.0N 126.9W   45 KT  50 MPH
 24H  23/1800Z 14.9N 129.2W   45 KT  50 MPH
 36H  24/0600Z 15.0N 131.3W   40 KT  45 MPH
 48H  24/1800Z 15.2N 133.1W   40 KT  45 MPH
 72H  25/1800Z 16.3N 135.9W   35 KT  40 MPH
 96H  26/1800Z 17.3N 138.6W   30 KT  35 MPH
120H  27/1800Z 18.0N 141.5W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Blake