San Onofre State Beach • Statistics for December

December: Peak Season at San O

December is the pinnacle of the surf year at San Onofre. The average swell height is 3.3ft (1.0m), and the average period is a solid 12.6s, but the real story is the wind and swell alignment. W swell leads at 55%, WSW at 29%, and SW at 11%, giving the exposed southwest-facing beach a healthy mix of groundswell and western hemi energy. Wave heights are centered in the 2-5ft (0.5-1.5m) range, with a meaningful 7% in the 5-7ft (1.5-2m) bracket and occasional 7-8ft (2-2.5m) sets. This is classic, powerful, lined-up Southern California winter surf.

Wind quality is tied with January for the best of the year, with ideal conditions 53% of the time. The offshore quadrant N, NNE, NE and ENE represents about 34% of all wind observations, and onshore winds are down to just 17%. These frequent offshore/drainage events groom the surf and keep the faces clean, especially in the morning. Air temperatures average 13.1°C, water temperature is 14.6°C, and rainfall picks up to 1.70 mm/day. When winter storms in the North Pacific fire up, December gives you those glassy, long-period, offshore days that make San Onofre legendary.