Some accidents are preventable.

Period. The wave period carrying the most energy, which is the time for two successive crests to pass a fixed point. It is not the time between sets.

Height. The average height of the highest one third of all waves over a twenty minute sample. Buoy readings combine swell and locally generated wind waves.

Direction. The direction the waves at the dominant period are coming from, not the direction they are heading.

Wind. The direction the wind is coming from at the buoy, offshore, with speed averaged over an eight minute period and the highest gust in that time, in miles per hour.

Tides. NOAA's predicted high and low tides for today, in feet above mean lower low water, drawn as the day's tide curve with a marker for now. Tap a station to switch between Half Moon Bay, the Golden Gate and Bodega Harbor. Each beach page shows the tide for its nearest station.

Source: NOAA National Data Buoy Center; NOAA CO-OPS tide predictions