May Gray and June Gloom
Aviara platinum is weeks 24-40, the rest is gold.
I have lived in the San Diego area for the past 30 years and we have the two phrases "May Gray" and "June Gloom". It refers to a weather condition along the coast where most of the day has fog. Sometimes very heavy overcast or fog. So, if you are traveling to Aviara in May and June you could have all day fog. But it is still pretty nice albeit a bit cool. On days when it is overcast, consider going to the SD Safari Park, Palomar Mtn., Anza Borrego state park (its a desert), and Temecula (wine country). All of these locations are inland and typically don't have the problem with being overcast.
I think that the weather along the coast is really pretty nice from July through the end of October and some years into November. The ocean temperature never gets really warm. The warmest is perhaps 74 degrees (only some years). So if you're in the water over an hour or hour and a half you might feel a bit chilled. But typically it doesn't get up to 70 until August IIRC. I've rented a wet suit when I've been in Hawaii in the winter. I would think that it would make ocean swimming much more enjoyable in the San Diego area.
So I would think that chosing a Gold week on the edges of the Platinum week would be pretty good. I would tend to avoid weeks 24, 25 and 26. But it varies from year to year. Last year was a cool year and we had a lot of overcast days in July. This year is "supposedly" going to be a warmer year.