000 WTPZ42 KNHC 220253 TCDEP2 Tropical Storm Greg Discussion Number 19 NWS National Hurricane Center Miami FL EP072017 800 PM PDT Fri Jul 21 2017 Greg is continuing to experience significant vertical shear, as the deep convection is only observed in the northeastern semicircle and its center is on the edge of the convective overcast. A blend of subjective Dvorak estimates from SAB/TAFB, objective Dvorak from CIMSS, and an ATMS analysis all suggest about 45 kt maximum sustained winds, unchanged from the previous advisory. Vertical shear analysis from CIMSS suggests substantially stronger tropospheric vertical shear than analyzed by either the GFS or ECMWF global models. The southwesterly shear appears to due to a vigorous upper-level trough north-northwest of Greg. While the shear should subside some as the upper trough and Greg move away from each other, the atmosphere that Greg will move through should become progressively drier and more stable. Around day 5, the hostile thermodynamics are expected to cause Greg to lose deep convection completely and thus become a remnant low. The official intensity forecast - showing little to no intensification before a gradual decay starting around day 3 - is based upon the HCCA corrected consensus technique and is slightly lower than that of the previous advisory. Greg is moving toward the west at about 12 kt, as it is moving along the southern periphery of a subtropical ridge. A gradual bend toward the west-northwest is anticipated around day 4 and 5, as a weakening Greg should be advected along by the low-level trades. The model guidance is in good agreement for this scenario - except for the GFS which has a sharp turn toward the northwest. This appears to be due to a stronger, deeper Greg being more affected by an approaching upper-level trough. This GFS solution is not, however, mirrored by most of the GEFS ensemble members which show more of a west to west-northwest track. The official track prediction is based upon the TVCN multi-model consensus with the GFS replaced by the GEFS ensemble mean and is nudged slightly southwest from the previous advisory. The initial wind radii was contracted inward some based upon the ATMS analysis from 2129Z. The official wind radii forecast is closest to the RVCN consensus approach. FORECAST POSITIONS AND MAX WINDS INIT 22/0300Z 15.1N 121.8W 45 KT 50 MPH 12H 22/1200Z 15.3N 123.5W 45 KT 50 MPH 24H 23/0000Z 15.5N 125.7W 45 KT 50 MPH 36H 23/1200Z 15.5N 128.0W 50 KT 60 MPH 48H 24/0000Z 15.5N 130.4W 50 KT 60 MPH 72H 25/0000Z 15.8N 133.6W 45 KT 50 MPH 96H 26/0000Z 17.1N 136.5W 35 KT 40 MPH 120H 27/0000Z 18.0N 139.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Landsea/Ramos