ZCZC MIATCDEP4 ALL TTAA00 KNHC DDHHMM Hurricane Hilary Discussion Number 8 NWS National Hurricane Center Miami FL EP092023 300 AM MDT Fri Aug 18 2023 Hilary's satellite presentation has continued to improve overnight, with a solid ring of cold cloud tops surrounding a warming eye. TAFB and SAB provided consensus Dvorak estimates of T6.0/115 kt while objective estimates are a bit higher, between 125-135 kt. The advisory intensity is therefore set at 125 kt as a blend of the various estimates. Hilary has rapidly intensified by a remarkable 65 kt over the past 24 hours. The hurricane remains large, and the initial wind radii have been adjusted based on a recent ASCAT-C pass. An Air Force Reserve Hurricane Hunter aircraft is scheduled to investigate Hilary around midday and should provide a more precise estimate of the hurricane's intensity. The hurricane continues to move toward the west-northwest, or 300/11 kt. However, with mid-tropospheric high pressure nudging eastward from the Rocky Mountains into the Central Plains, and a cut-off low off the California coast, Hilary is expected to turn northwestward very soon and then turn northward and begin accelerating by 48 hours. The track guidance is more tightly clustered than usual during the first 72 hours of the forecast, and therefore there is relatively high confidence in the NHC track forecast, which is essentially unchanged from the previous advisory. Since Hilary's forecast track parallels the coast from the central Baja California peninsula northward to southern California, it is still nearly impossible to predict an exact landfall location, not to mention that Hilary's exact landfall probably won't make much difference when it comes to the expected hazards and impacts in the region. Hilary could strengthen a little more during the next 12 hours or so. However, once hurricanes reach major hurricane strength, they are prone to fluctuations in intensity, particularly if an eyewall replacement begins. In addition, oceanic heat content will be dropping significantly in 24-36 hours, and it's likely that Hilary's large wind field will mix up cooler water ahead of the arrival of the center. This colder water, as well as potential interaction with the terrain of the Baja California peninsula, is expected to induce faster weakening over the weekend, with Hilary likely to drop below hurricane intensity some time on Sunday. Due to its accelerating motion in 2 to 3 days, Hilary is still expected to be producing tropical-storm-force winds when it reaches southern California. The surface circulation is likely to dissipate soon after moving into California, but a day 4 remnant low point is still shown over the western U.S. for continuity purposes. KEY MESSAGES: 1. Heavy rainfall associated with Hilary may produce areas of flash flooding and result in landslides over portions of the Baja California Peninsula from late today into late Sunday. Rainfall impacts from Hilary within the Southwestern United States are expected to peak this weekend into Monday. Flash, urban, and arroyo flooding is expected with the potential for significant impacts. 2. The threat of hurricane-force wind impacts is increasing along the west-central coast of the Baja California Peninsula, where a hurricane watch is in effect. Tropical storm conditions are expected to begin across the southern portion of the Baja California Peninsula later today and then spread northward through the weekend. 3. The threat of significant wind impacts continues to increase for the northern portions of the Baja California Peninsula and the Southwestern United States, especially in areas of mountainous terrain. Although it is too soon to determine the location and magnitude of these impacts, interests in these areas should monitor the progress of Hilary and updates to the forecast. Watches could be issued for portions of this area, including along the southern California coast, later today. 4. Large swells from Hilary will spread northward along the coast of southwestern Mexico and the Baja California Peninsula. These swells will reach the Gulf of California and northern portions of the Baja California Peninsula later this weekend. FORECAST POSITIONS AND MAX WINDS INIT 18/0900Z 17.2N 110.8W 125 KT 145 MPH 12H 18/1800Z 18.3N 112.0W 130 KT 150 MPH 24H 19/0600Z 20.2N 113.2W 120 KT 140 MPH 36H 19/1800Z 22.4N 114.0W 105 KT 120 MPH 48H 20/0600Z 25.3N 114.7W 85 KT 100 MPH 60H 20/1800Z 28.7N 115.6W 65 KT 75 MPH 72H 21/0600Z 32.9N 116.7W 50 KT 60 MPH...INLAND 96H 22/0600Z 43.6N 117.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 23/0600Z...DISSIPATED $$ Forecaster Berg NNNN