In August it'll be hot, no lying to you about that. But it is much better than Orlando. Unless there is an immediate thunderstorm, there will be low humidity in Anaheim. The heat can average in the 80's and 90's but there is the once in a blue moon heatwave where it'll be well into the 100's. But still, without the humidity it beats Orlando hands down.
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Just plan on drinking LOTS of water, staying in the shade whenever you can, have small breaks to sit & cool off (more & more queues are indoors these days which helps), and if you are like me (sweats if it's over 75 degrees) carry a small fan or mister bottle with you.