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ZCZC MIATCDEP5 ALL TTAA00 KNHC DDHHMM Hurricane Rosa Discussion Number 18 NWS National Hurricane Center Miami FL EP202018 800 AM PDT Sat Sep 29 2018 Rosa has become significantly better organized during the last several hours, likely due to the completion of an eyewall replacement cycle before the center moved over cold water. The storm now has a 30-40 n mi wide eye, and the eyewall convective tops have become much colder and more symmetric. The initial intensity has been increased to 90 kt based on a blend of various satellite intensity estimates, and it is possible that this intensity is conservative. The hurricane has good to excellent cirrus outflow in the northeastern semicircle. The current re-intensification was poorly anticipated, and it is unclear how much more strengthening will occur before Rosa reaches the 26C isotherm in about 12 h. Even if the hurricane strengthens a little more, the combination of decreasing sea surface temperatures and increasing shear should cause steady to rapid weakening after 12 h, and the new intensity forecast still calls for the cyclone to weaken below hurricane strength before the center reaches the Baja California peninsula between 48-72 h. After landfall, Rosa is expected to weaken even faster, and the surface circulation is forecast to dissipate just after 72 h in agreement with all of the dynamical models. However, the mid-level circulation and the associated rainfall will continue moving across the southwestern United States after the surface circulation dissipates. The initial motion is now 355/10. During the forecast period, the hurricane will recurve into the westerlies between a deep-layer ridge over northern Mexico and a large mid- to upper-level trough over California and the adjacent Pacific. This should result in a continued northward motion through tonight, followed by a turn toward the north-northeast on Sunday. The new forecast track is similar to, but a little faster than, the previous track and lies near the consensus models. On the forecast track, the center of Rosa will move near or over the central and northern portions the Baja California peninsula on Monday and Monday night, and then move into the southwestern United States on Tuesday. 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 starting on Monday. Interests in those locations should monitor the progress of Rosa. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 20.5N 118.4W 90 KT 105 MPH 12H 30/0000Z 22.0N 118.6W 90 KT 105 MPH 24H 30/1200Z 23.9N 118.4W 75 KT 85 MPH 36H 01/0000Z 25.9N 117.6W 60 KT 70 MPH 48H 01/1200Z 27.7N 116.7W 45 KT 50 MPH 72H 02/1200Z 33.0N 114.0W 25 KT 30 MPH...INLAND 96H 03/1200Z...DISSIPATED $$ Forecaster Beven NNNN