San Diego is temperate water diving. Temperatures range from the low 70's to the low 50's depending on conditions and time of year. The best diving is usually in the fall. The water temperatures are warmer, but the visibility is still good. In shore visibility is usually 10 to 15 feet. Offshore vis is typically 30 feet.
Generally speaking, you'll need a largish amount of artifical blubber. A 6mm wetsuit, booties, hood and gloves are the usual. All this neoprene requires weight. If you're used to tropical diving, adjust accordingly. 2 piece suits need more weight than the one piece suits.
We highly recommend you carry a compass, light, and knife.
When you get to your dive site, spend a few minutes watching the waves. Knowing the sets, heights, and breaker zone will make the difference between a pleasant entry, and a ride through the washing machine ["getting Maytagged" is the local term].
The San Diego Lifeguard Service operates a beach and weather report that provides diving conditions for La Jolla Shores, and La Jolla Cove.You should check the report at 619-221-8824 before doing any shore diving. Conditions in other parts of La Jolla will be comparable to La Jolla Cove.
Unfortunately, you need to pay particular attention to areas closed due to contamination. These are almost always Children's Pool, frequently inside Mission Bay, or can also be along the ocean due to sewage spills.
Boat diving is more reliable than shore diving. We have several wrecks, and the kelp beds are a "must do," particularly if you've never dived in kelp before. OES members are very partial to the Lois Ann. We recommend her to all.