ZCZC MIATCDEP2 ALL TTAA00 KNHC DDHHMM Tropical Storm Greg Discussion Number 11 NWS National Hurricane Center Miami FL EP072017 900 PM MDT Wed Jul 19 2017 Greg's convective pattern has not improved this evening, with most of the associated shower and thunderstorm activity concentrated to the south and west of the center. Since subjective and objective Dvorak estimates have either remained steady or fallen from six hours ago, the initial intensity is held at 40 kt based on the earlier ASCAT passes. Greg's initial motion is westward, or 270/9 kt. A strong mid- to upper-level ridge axis extending westward from northern Mexico should cause Greg to move westward or west-northwestward for the entire forecast period, but at a slightly faster forward speed beginning in about 24 hours. The biggest forecast challenge for Greg's track is its forward speed, since there is a notable difference between the faster ECMWF and the slower GFS and HWRF models. Longitude-wise, the updated NHC forecast is close to the TVCN multi-model consensus. However, a slight shift in the overall guidance envelope required a bit of a southward nudge compared to the previous forecast. It's not exactly clear why Greg's convection has not become any better organized since the analyzed deep-layer shear is less than 10 kt. However, products from UW-CIMSS do suggest that there is 15-20 kt of mid-level shear extending northeast of Greg's center, which could be disrupting the convection in that quadrant. Assuming that the ambient environment slowly improves over time, Greg should be able to eventually become better organized and strengthen as indicated by most of the intensity models. The updated NHC forecast has been bumped up slightly at 24 hours and beyond to be a little closer to the intensity consensus. However, this new forecast is still 10-15 kt below the usually reliable models like HWRF, HCCA, and Florida State Superensemble, just in case Greg continues to struggle in becoming better organized. FORECAST POSITIONS AND MAX WINDS INIT 20/0300Z 14.1N 113.6W 40 KT 45 MPH 12H 20/1200Z 14.3N 115.0W 45 KT 50 MPH 24H 21/0000Z 14.8N 117.1W 55 KT 65 MPH 36H 21/1200Z 15.2N 119.3W 60 KT 70 MPH 48H 22/0000Z 15.6N 121.7W 65 KT 75 MPH 72H 23/0000Z 15.7N 126.8W 65 KT 75 MPH 96H 24/0000Z 15.3N 131.6W 55 KT 65 MPH 120H 25/0000Z 15.5N 135.5W 45 KT 50 MPH $$ Forecaster Berg NNNN
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