For some reason, about 90% of my customers seem to have me detailing their cars in areas that have no available shade. And summer here in Central Florida is easilly hitting the high 90s regularly.
I agree with Beemerboy...keep that car wet and wash in panels. Don't let the soap sit long. And keep going back and re-wetting the places you've already washed.
I have a quick shade and I like it.... 12' X 12' - $130 at Lowes. I also keep a 10 X10 tarp with some bungees so I can extend it when I have to for large vehicles.
And I currently use a drying agent in my water tank called "Ultra Shine" from Flash products. It is advertised to dry spot free even in the hot sun...but I still notice spots if I let it dry on its own. However, the spots seem easier to remove than normal water spots. (Anyone know of a better product?)
And I also QD while I'm drying. I learned that trick right here on Detail City! It definitely makes a difference.