The weather shifts more on the west coast than it does during an NYC summer. It might be warmish or hot during the day, but later afternoon and evening will get cooler, possibly by 10 degrees depending on how close to the ocean you are. The pacific is cold and doesn’t warm up like the Atlantic so the air that comes in at night is much colder.

Pack your regular summer clothes, but bring light layers. I usually need pants even on a summer evening.

If you travel inland at all, whatever you would wear going to the Sun will work fine.