000 WTPZ44 KNHC 210243 TCDEP4 Tropical Storm Roslyn Discussion Number 5 NWS National Hurricane Center Miami FL EP192022 1000 PM CDT Thu Oct 20 2022 Roslyn looks better organized on satellite imagery this evening. Deep convection has increased near and over the estimated center position, and the expanding dense convective overcast has cloud tops colder than -75 to -80 deg C. The objective UW-CIMSS ADT and SATCON estimates have increased to 40-45 kt, and SAB and TAFB provided consensus T3.0/45 kt Dvorak estimates at 00 UTC. Based on these data, the initial intensity is raised to 45 kt for this advisory. Roslyn is moving west-northwestward at 285/7 kt, steered by a mid-level ridge to the north and northwest of the cyclone. As this ridge shifts eastward during the next couple of days, the cyclone will become steered by the flow between the ridge and a deep-layer trough to the northwest, well offshore of southern California. This should induce a turn toward the north and north-northeast this weekend, eventually bringing the center of Roslyn inland along the coast of west-central Mexico. There is still a large spread in the track guidance beyond 48 h regarding how sharply the cyclone recurves and how fast it moves inland. The GFS remains on the right side of the guidance envelope and brings Roslyn inland early Sunday, while several other models show a slower and more gradual recurvature with landfall later in the day. Overall, little change was made to the NHC track forecast, which still lies slightly east of the TVCE and HCCA aids. The cyclone will move over warm sea surface temperatures within a weak deep-layer shear environment during the next couple of days or so. This is expected to support strengthening, and Roslyn is forecast to become a hurricane by late Friday with continued intensification over the weekend. Given the favorable environmental conditions, the NHC intensity forecast lies on the high end of the guidance, generally between the IVCN and HCCA aids. While rapid intensification is not explicitly forecast, the GFS-based DTOPS guidance shows a 44 percent chance of a 25-kt increase in intensity during the next 24 h. Beyond 48 h, the intensity will be dependent on the cyclone's track and whether it remains far enough offshore to avoid the negative influences of land. The official forecast shows Roslyn inland and rapidly weakening by 72 h, with dissipation soon thereafter over the mountains of western Mexico. Key Messages: 1. Roslyn is forecast to become a hurricane before it passes near or over the west-central coast of Mexico late Saturday and Sunday, accompanied by strong winds and a potentially dangerous storm surge. A Hurricane Watch has been issued for the coast of mainland Mexico from Playa Perula northward to San Blas, and additional watches or warnings will likely be required on Friday. 2. Heavy rainfall could lead to flash flooding and possible landslides in areas of rugged terrain over coastal southwestern and west-central Mexico. FORECAST POSITIONS AND MAX WINDS INIT 21/0300Z 15.7N 103.6W 45 KT 50 MPH 12H 21/1200Z 16.0N 104.4W 55 KT 65 MPH 24H 22/0000Z 16.7N 105.3W 65 KT 75 MPH 36H 22/1200Z 17.9N 106.2W 75 KT 85 MPH 48H 23/0000Z 19.5N 106.6W 85 KT 100 MPH 60H 23/1200Z 21.3N 106.5W 85 KT 100 MPH 72H 24/0000Z 23.4N 105.6W 45 KT 50 MPH...INLAND 96H 25/0000Z...DISSIPATED $$ Forecaster Reinhart