Wedding Wardrobe Help?

Hubby and I will be in coastal, northern California in early May for a wedding. I checked the forecast and it is expected to be in the 50s-60s. That reads cold to my southern blood! My closet is underprepared? So what would you wear? The wedding is at 5pm in a home on the coast. Knowing the couple, it should veer more casual than formal. Suggestions?