ZCZC MIATCDEP4 ALL TTAA00 KNHC DDHHMM Hurricane Hilary Discussion Number 13 NWS National Hurricane Center Miami FL EP092023 900 AM MDT Sat Aug 19 2023 Although Hilary continues to maintain a well-defined circular eye, the convective pattern has become increasingly asymmetric during the past several hours. Deep convection has been eroding on the system's west side as dry and stable air has been wrapping into that portion of the circulation. A blend of the latest satellite intensity estimates supports nudging the initial intensity downward to 110 kt for this advisory. The Air Force Hurricane Hunters are scheduled to investigate the system later today, and the data they collect will provide a better assessment of Hilary's intensity and structure. The major hurricane continues to turn to the right, and the latest initial motion is north-northwestward, or 345/14 kt. The steering currents are well established and consist of a strong mid-level high pressure area over the south-central U.S. and a mid- to upper-level low off the central California coast. The flow between these features should cause Hilary to accelerate to the north-northwest or north during the next day or two, with the core of the system reaching the central portion of the Baja California Peninsula tonight and southern California Sunday afternoon or evening. Users are reminded that the exact details of the track forecast, including where Hilary might make landfall, are of little overall importance since strong winds and heavy rainfall will extend far from the center. These hazards will also begin well in advance of the arrival of the center. Hilary is expected to weaken quickly while it moves northward due to significantly cooler waters, drier air, and an increase in vertical wind shear. Even though weakening is anticipated, Hilary is still expected to be a hurricane when it moves near or over the central portion of the Baja California peninsula, but is expected to decay to a tropical storm before it moves over southern California. The intensity models are in good agreement, and the NHC forecast is near the middle of the guidance envelope. KEY MESSAGES: 1. Preparations for flooding impacts should be completed as soon as possible, as heavy rainfall will begin well in advance of the center. In the Southwestern U.S., the potentially historic amount of rainfall is expected to cause flash, urban, and arroyo flooding including landslides, mudslides, and debris flows. Dangerous to locally catastrophic flooding impacts are expected late tonight through early Monday. 2. Hurricane conditions are expected along the west-central coast of the Baja California Peninsula within the hurricane warning area tonight and Sunday morning, and are possible in the Hurricane Watch area on Sunday. 3. Tropical storm conditions are expected to begin Sunday afternoon in portions of the southwestern U.S. within the Tropical Storm Warning area. Winds could be particularly strong and gusty in and near areas of higher terrain. 4. Large swells generated by Hilary will affect portions of the Baja California Peninsula and southern California over the next couple of days. These swells are likely to cause life-threatening surf and rip current conditions. FORECAST POSITIONS AND MAX WINDS INIT 19/1500Z 22.3N 113.5W 110 KT 125 MPH 12H 20/0000Z 24.6N 114.1W 90 KT 105 MPH 24H 20/1200Z 28.3N 115.2W 70 KT 80 MPH 36H 21/0000Z 33.4N 116.7W 50 KT 60 MPH...INLAND 48H 21/1200Z 39.6N 117.4W 30 KT 35 MPH...POST-TROP/INLAND 60H 22/0000Z...DISSIPATED $$ Forecaster Cangialosi NNNN
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Page last modified: Monday, 18-Dec-2023 12:10:11 UTC