WTPZ42 KNHC 211500

Tropical Storm Greg Discussion Number 17
NWS National Hurricane Center Miami FL EP072017
800 AM PDT Fri Jul 21 2017

Satellite images indicate that the central convection associated with Greg has become more compact over the last several hours, though it is mostly on the northern side of the circulation. Microwave data also show an increase in organization with a thin mid-level eye feature now apparent. Although the conventional satellite estimates haven't changed, based on the increased structure in microwave data, the initial wind speed is bumped up to 50 kt, a blend of the latest CI estimates from TAFB/SAB.

The initial motion is a more confident 285/9. A trough to the northwest of Greg is forecast to lift northward during the next couple of days, which will probably cause Greg to shift to a more westward track by Sunday as a ridge builds in slightly. The short-term forecast has been shifted northward, similar to the model consensus. In the longer range, the storm should turn to the west-northwest or northwest due to a small low- to mid-level trough dropping out of the mid-latitudes, weakening the periphery of the aforementioned ridge. Model guidance, however, is not in good agreement on the long range forecast, with many of the differences due to the strength of the storm. It is probably prudent to wait until the 12Z models come in to see if the ECMWF continues its previous solution, which the prior NHC forecast weighted heavily. Thus the new NHC track forecast is basically an update of the last forecast, on the western side of the model consensus at days 4 and 5.

Greg has a couple of days over warm water left to strengthen. However, the environment is less than optimal, with light-to- moderate southerly shear and a drying mid-level atmosphere forecast. On the other hand, Greg is finally displaying a more solid inner core, which would generally promote strengthening. Overall, these factors support some intensification during the next couple of days, and that is the solution shown in the latest NHC forecast. Gradual weakening should begin by day 4 due to colder waters.


INIT 21/1500Z 15.1N 119.2W 50 KT 60 MPH 12H 22/0000Z 15.4N 120.7W 55 KT 65 MPH 24H 22/1200Z 15.7N 122.8W 60 KT 70 MPH 36H 23/0000Z 15.9N 125.1W 65 KT 75 MPH 48H 23/1200Z 16.0N 127.4W 65 KT 75 MPH 72H 24/1200Z 16.2N 130.8W 60 KT 70 MPH 96H 25/1200Z 17.1N 133.9W 50 KT 60 MPH 120H 26/1200Z 18.5N 136.5W 40 KT 45 MPH

$$ Forecaster Blake