Sholin, it was very hot in Seville which is where I spent the most time. It was in the mid 90s during the day and wasn't too humid. I'd say nights were in the upper 60s. It didn't seem to get dark until around 10.30 or so and that let me get in a lot of things after the hottest part of the day. I heard one tourist at the bullring saying the weather reminded her of Amarillo Texas in the summer.

If you go I'd recommend a private guide for at least one day. These guides know what tourists like and dislike because they work with so many on a daily basis. They also know hidden places and where to eat when every restaurant seems to be closed closed at midday. You pay more upfront but then there's a lot of things you'll visit that are absolutely free that most tourists never see.