000 WTPZ45 KNHC 130240 TCDEP5 Hurricane Darby Discussion Number 15 NWS National Hurricane Center Miami FL EP052022 500 PM HST Tue Jul 12 2022 Darby remains an impressive hurricane in conventional satellite imagery, however the eye is not as defined as it was earlier today. As noted in the previous discussion, the hurricane is more asymmetric with the cloud shield favoring the western semicircle. A 0043 UTC SSMIS microwave overpass revealed some erosion of the convection over the northern semicircle which is suggestive of some dry air entrainment over that portion of the circulation. A blend of the TAFB and SAB subjective Dvorak T- and CI-numbers yields an initial intensity of 95 kt. This is also supported by the latest UW/CIMSS ADT and SATCON estimates which are 95 and 98 kt, respectively. Although the vertical shear is expected to remain quite low during the next 24 hours, Darby will be moving over marginal sea surface temperatures, which is expected to cause gradual weakening. After that time, a sharp increase in vertical wind shear and SSTs of 24 to 25 degrees Celsius should result in continued weakening. Simulated satellite imagery from the global models suggest Darby will cease to produce deep convection in a few days and the NHC forecast calls for the system to become a post-tropical cyclone in about 72 hours. The remnant low is expected to degenerate into a trough by day 5, and this is reflected in the NHC forecast. There is not much spread in the intensity model guidance and the official forecast is in good agreement with the SHIPS, ICON, and HCCA intensity aids. Darby remains on a steady westward motion at about 15 kt. A slightly slower westward to west-northwestward track is expected by Wednesday as the tropical cyclone nears a break in the subtropical ridge. After 48 hours, a weaker Darby should turn back westward as the low-level trade wind flow becomes the more dominant steering layer. Although there is very little cross-track spread in the dynamical model guidance, the envelope has shifted slightly southward this cycle, and the NHC forecast has been adjusted accordingly. The new NHC track forecast is near the GFEX and TVCE consensus models. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 14.6N 132.7W 95 KT 110 MPH 12H 13/1200Z 14.9N 134.8W 85 KT 100 MPH 24H 14/0000Z 15.4N 137.4W 75 KT 85 MPH 36H 14/1200Z 16.1N 140.0W 65 KT 75 MPH 48H 15/0000Z 16.6N 142.4W 55 KT 65 MPH 60H 15/1200Z 16.8N 145.0W 45 KT 50 MPH 72H 16/0000Z 16.9N 148.0W 35 KT 40 MPH...POST-TROPICAL 96H 17/0000Z 16.8N 154.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 18/0000Z...DISSIPATED $$ Forecaster Brown