000 WTPZ44 KNHC 202036 TCDEP4 Tropical Storm Roslyn Discussion Number 4 NWS National Hurricane Center Miami FL EP192022 400 PM CDT Thu Oct 20 2022 Satellite imagery shows that Roslyn has become a little more organized this afternoon, with the formation of a curved convective band near the center in the eastern semicircle. The various subjective and objective satellite intensity estimates have increased a little since the last advisory, and the initial intensity is increased to 40 kt in best agreement with the CIMSS satellite consensus. It should be noted that Roslyn looks a little sheared, with the center near the western edge of the convection and a lot of curved low cloud lines apparent west of the convection. It is uncertain why the cyclone looks this way since the analyzed vertical wind shear is less than 10 kt. The initial motion is now 280/6 kt. A mid- to upper-level ridge is located over Mexico north and northwest of Roslyn, while a deep-layer low pressure area is located several hundred miles southwest of the coast of southern California. The large-scale models forecast both of these features to move eastward, with Roslyn expected to recurve to the north and northeast between them. While the track guidance is in good agreement with this general scenario, there is a significant spread in the guidance regarding how far west the cyclone will move before recurvature. The GFS is on the right side of the envelope, bringing the center near Cabo Corrientes in roughly 60 h and inland over mainland Mexico thereafter. On the other hand, the ECMWF and UKMET are about 150 n mi west of the GFS at that time, keeping the center farther offshore and showing a more northerly landfall point in mainland Mexico. Overall, the guidance envelope has shifted a little to the west since the last advisory. The new forecast track is also shifted west of the previous track, but it lies to the east of the consensus models out of deference to the previous forecast and the GFS. Roslyn remains over warm sea surface temperatures in a moist, light-shear environment. These conditions are likely to persist for the next 60-72 h, and they should allow Roslyn to steadily intensify. After that time, the intensity forecast becomes more uncertain due to a forecast increase in shear, the possibility of dry air entrainment, and the uncertainty of how much land interaction will occur. The new intensity forecast is again similar to the previous forecast and calls for a peak intensity of 85 kt before landfall in mainland Mexico. After landfall, rapid weakening is expected, with the cyclone dissipating over the mountains of Mexico between 96-120 h. 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. Interests along the coast of southwestern and west-central Mexico should closely monitor the progress of this system. A tropical storm watch has been issued for part of this area, and additional hurricane or tropical storm watches could be required tonight or on Friday. 2. Heavy rainfall could lead to flash flooding and possible landslides in areas of rugged terrain over coastal southwestern Mexico. FORECAST POSITIONS AND MAX WINDS INIT 20/2100Z 15.5N 103.0W 40 KT 45 MPH 12H 21/0600Z 15.8N 103.7W 45 KT 50 MPH 24H 21/1800Z 16.3N 104.6W 55 KT 65 MPH 36H 22/0600Z 17.2N 105.7W 65 KT 75 MPH 48H 22/1800Z 18.5N 106.3W 75 KT 85 MPH 60H 23/0600Z 20.0N 106.5W 85 KT 100 MPH 72H 23/1800Z 21.8N 106.0W 85 KT 100 MPH 96H 24/1800Z 25.0N 104.5W 25 KT 30 MPH...INLAND 120H 25/1800Z...DISSIPATED $$ Forecaster Beven