Yes. Water temperatures around here stay below 70 degrees, which is wonderful. Air temperatures at the end of June should be in the 70s. The normal June gloom might have worn off, so there is a slight chance that it might reach the 80s. If you stay by the coast though, there should be no issues with the heat.
I would definitely reccomend Catalina as a day trip. It is wonderful! The weather might be a little bit warmer out on the island, but it's not going to be ridiculous. The cool ocean winds generally balance out any heat issues.