It can be pretty hot in August depends on the cycle of the weather. Can be like 85-90 or so and a little humid sometimes. Some night and morning fog if it is cool enough.
Winter in San diego doesn't start til like december but then it is still ok, can be hot or rain, depends on the weather cycle..... . like 70-80 day and 40-50 at nght. Even if it is raining, it is like over 70 deg.
Sea World is neat, they put Shamu and a few others in a new stadium and don't forget to go see the Clydsdales in the eastern part of the park. sometimes they hook them up to the wagon and tool them around a bit.
If you are able to go to sea world on a weekday, like monday or turesday, almost any of them has less crowds.
Remember to also go to the world famous San Diego Zoo. there are alot of interresting animals in there, pretty big... ... .
Have fun and don't forget the sunscreen!!