I ran a script on my wave height log to plot mean and max set height (per Surfline) by month. The data goes back to mid-2006 and counts a few of the popular SD breaks (Blacks, Cardiff, etc.).

Dark blue is maximum set height. Light blue is average set height. The dots correspond to the right hand axis and represent the number of data points for that category.

I have a feeling the low data point count for June - September means there are a number of flat days that the script skips over. So the light blue line might actually be closer to one.

That aside, the mean wave height doesn't change much by month. This is probably because the big days we get in December are offset by trashy days on account of wind.

Of course, if you're looking for the big days, look no further than December, February, and April.

For anyone interested in the gaseofinancial impact of motorcycle ownership, here are the monthly gas expenses for the past couple years. They're normalized to $4/gallon based on average SD gas price for that month.

I did some quick and dirty averages, discounting May 2006 where 'froading added to the gas expenditure. Also I did not factor in December 2007 as it featured a road trip from Oregon to San Diego.
A few notes: