Assuming the plant has sun scald, consider these two short/long term suggestions.

Short term...Try to purchase a 70% shade cloth from a local nursery to temporarily protect the plant. You can also improvise. I had to protect a hydrangea after a thunderstorn damaged a Crape Myrtle; I used cardboard to create a contraption that lasted thru what was left of summer.

Long term....You may need to transplant the shrub to an area that where it will receive less sun. For ideas of where to move it to, walk around your garden around 11am-1pm and observe which area(s) receive shade starting at that time. Then review the plant label and determine the plant size at maturity (height and width). Determine if the shaded area will be appropriate based on the shrubs' height and width at maturity. Next, determine if the area is also appropriate. Make sure the sprinkler or drip irrigation reach there so you can water during dry times. Make sure the area is not water logged for long periods after it rains. I assume your soil drains well and has acidic soil.

Can I ask you some questions? What is the name of this variety? Could you post a detailed description of the problem that you see happen with the leaves and then some pictures? I suggest one picture of the whole bush that shows the affected areas. Then a couple more showing the leaf damage (leaf close ups, top and bottom of leaves)? Lastly, can you indicate where are you located (Zone and city-state) and when exactly does the shrub get sun (starting when; until when)?

The pictures can allow others to confirm your the diagnosis. Most shrubs can withstand sun if they get afternoon shade and I am puzzled as to why yours is suffering from sunscald if it gets afternoon shade. Record heat without rain, on the other hand, may suggest a moisture issue nor sunscald.

Thanks,
Luis

Thank you for your response Luis. I'm sorry, but I do not know the name of this variety. It is about 26 years old and was here when we bought the house. I live outside of Philadelphia, PA, zone 6, I believe. I felt that sun scald seemed like a reasonable diagnosis because growth that was not previously exposed to light is now being affected. Perhaps it is a moisture issue though. I will try to get some pictures posted in a few minutes.

So, I am having trouble with my camera but I searched around and found an old post with pictures that look like my plant (the pictures at the top). The leaves have rust colored blotches that primarily start in the center of the leaves but there are a couple leaves with spots on the edges. The spots seem to be spreading quickly and appear on areas that have been pruned.

Here is a link that might be useful: Sun scald pictures

There isn't much you can to. The damage is not reversible. To prevent further damage you can put on a white netting until the newly exposed leaves get a chance to toughen.

Whenever you prune an rhdodendron or azalea you are exposing the newly exposed leaves to sun scald. That is a good reason to prune immediately after blooming when the sun/heat stress is less.

It will be just fine when new leaves come out next year. But until then it will look a little scorched.