* WHAT...For the High Surf Advisory, large breaking waves of 20 to 26 feet, including breakers near 30 feet at favored spots such as Mavericks. For the High Surf Warning, dangerously large breaking waves of 30 to 35 feet, including breakers up to 40 feet at favored spots such as Mavericks.

* WHERE...San Francisco, Coastal North Bay Including Point Reyes National Seashore, San Francisco Peninsula Coast, Northern Monterey Bay and Southern Monterey Bay and Big Sur Coast.

* WHEN...For the High Surf Advisory, until 4 PM PST this afternoon. For the High Surf Warning, from 4 PM this afternoon to noon PST Tuesday.

* IMPACTS...Life-threatening swimming and surfing conditions and significant beach erosion can be expected. Large waves can sweep across the beach without warning, pulling people into the sea from rocks, jetties and beaches. Sudden immersion in cold water can result in cold water shock even for the most experienced swimmers. Cold water shock can result in dramatic changes in breathing, heart rate and blood pressure, greatly increasing the risk of drowning in rough open waters.