WTPZ42 KNHC 230851

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.


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