000 WTPZ42 KNHC 210236 TCDEP2 Tropical Storm Greg Discussion Number 15 NWS National Hurricane Center Miami FL EP072017 800 PM PDT Thu Jul 20 2017 Greg's center is embedded between a large and persistent band of convection to the south and newly developing convection to the northeast, but the banding continues to have a tough time wrapping around the northwestern side of the circulation. Since Dvorak estimates from TAFB and SAB have not changed all day, and final-T ADT numbers have actually decreased, the initial intensity will remain 45 kt. Greg is located to the south of anomalously strong low- to mid-level ridging, which is pushing the cyclone westward with an initial motion of 275/9 kt. Greg is forecast to move on a westward or west-northwestward course for the rest of the forecast period, and there is good model agreement through 48 hours. After 48 hours, however, the spread in the model guidance is larger than normal. The GFS and HWRF, for example, show a stronger Greg moving more slowly toward the northwest by day 5. On the other hand, the ECMWF and UKMET have a weaker Greg moving faster and staying farther south, with some interaction with the remnants of T.D. Eight-E still possible. As a compromise between these two scenarios, the updated official forecast is just a little slower and south of the previous forecast on days 3 through 5, and it is not too far from the various model consensus aids. The environment seems as though it should be conducive for strengthening. However, Greg has defied that thought for the past day or so, as it seems that something about its structure has prevented it from benefiting from relatively low shear and warm SSTs. However, microwave data suggests that the cyclone has recently developed some improved low-level banding around the center, which could be a harbinger of a gradual intensification trend. The new NHC intensity forecast is basically the same as the previous one, showing Greg becoming a hurricane in 36 hours and then weakening on days 3 through 5 as it moves over progressively cooler waters. This forecast generally lies between the less aggressive statistical-dynamical models and the stronger HWRF and HCCA models. FORECAST POSITIONS AND MAX WINDS INIT 21/0300Z 14.3N 117.4W 45 KT 50 MPH 12H 21/1200Z 14.6N 118.8W 50 KT 60 MPH 24H 22/0000Z 15.1N 120.9W 60 KT 70 MPH 36H 22/1200Z 15.5N 123.0W 65 KT 75 MPH 48H 23/0000Z 15.7N 125.3W 70 KT 80 MPH 72H 24/0000Z 15.8N 129.9W 65 KT 75 MPH 96H 25/0000Z 16.1N 133.4W 55 KT 65 MPH 120H 26/0000Z 17.0N 136.0W 50 KT 60 MPH $$ Forecaster Berg