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Hurricane Rosa Forecast Discussion Number 17
2018-09-29 10:40:20| National Hurricane Center (East Pacific)
Issued at 200 AM PDT Sat Sep 29 2018 651 WTPZ45 KNHC 290840 TCDEP5 Hurricane Rosa Discussion Number 17 NWS National Hurricane Center Miami FL EP202018 200 AM PDT Sat Sep 29 2018 Rosa's satellite appearance has degraded significantly since the previous advisory with an eye no longer evident in infrared imagery. However, a well-defined low-level eye is evident in recent passive microwave imagery. A comparison of the two data sources indicate that the upper-level circulation is tilted to the east of the low-level eye by 12-18 nmi due to westerly shear of about 15 kt as assessed by UW-CIMSS. The initial intensity of 85 kt is based on a blend of satellite intensity estimates form TAFB, SAB, and UW-CIMSS ADT and SATCON. Rosa is moving northward now and the initial motion estimate is 350/08 kt. During the next 72 hours, the hurricane is forecast to move around the western periphery of a deep-layer ridge that extends from the Gulf of Mexico westward to Baja California, resulting in a northward motion today, and a turn toward the north-northeast at a faster forward speed on Monday and Tuesday as a mid-latitude trough approaches from the west. The latest NHC model guidance is tightly packed about the previous forecast track, so no significant changes were required. The new NHC track forecast lies close to a blend of the consensus models HCCA, FSSE, and IVCN. Rosa's intensity has decreased 40 kt during the past 24 hours, with the bulk of the weakening having occurred during the past 18 hours, and additional weakening is expected due to the cyclone moving over cooler water and into a regime of increasing southwesterly vertical wind shear of more than 30 kt by 48 hours. Although Rosa is currently located over 28 deg C SSTs, the depth of the warm water is quite shallow, so cold upwelling occurring beneath the hurricane will act to hasten the weakening process today. Rosa is forecast to approach Baja California as a tropical storm, and then quickly degenerate into a tropical and a remnant low as the cyclone moves across the mountainous terrain of northern Baja California and northwestern mainland Mexico. The official intensity forecast closely follows the intensity consensus models IVCN and HCCA. Key Messages: 1. The main hazard expected from Rosa or its remnants is very heavy rainfall in Baja California, northwestern Mexico, and the Desert Southwest. These rains are expected to produce life-threatening flash flooding and debris flows in the deserts, and landslides in mountainous terrain. For more information about potential rainfall in that area, please see products from the Weather Prediction Center and your local NWS forecast office. 2. Rosa could also bring tropical storm conditions to portions of the central and northern Baja California peninsula in a couple of days. Interests in those locations should monitor the progress of Rosa. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 19.2N 118.2W 85 KT 100 MPH 12H 29/1800Z 20.5N 118.4W 75 KT 85 MPH 24H 30/0600Z 22.5N 118.5W 65 KT 75 MPH 36H 30/1800Z 24.4N 118.1W 55 KT 65 MPH 48H 01/0600Z 26.2N 117.3W 45 KT 50 MPH 72H 02/0600Z 30.9N 115.0W 30 KT 35 MPH...INLAND NRN BAJA CALIF 96H 03/0600Z 38.0N 111.0W 15 KT 15 MPH...POST-TROP/REMNT LOW 120H 04/0600Z...DISSIPATED INLAND $$ Forecaster Stewart
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