Brown spots sounds like mildew, which may have been going to happen regardless of the rain. Look up rhododendron mildew.

Ditch them to provide drainage. This means digging trenches adjacent to the planting to drain away surface water so the rhododendron planting doesn't become saturated.

If you were very ambitious you could make a raised bed, but that is lots of work. Drainage is the most important thing with rhododendrons. Good Luck!

Yellowing of leaves surfaces, often with brownish burned areas, occurring on leaves that are more exposed to sun, is caused by more sun exposure than the plant is able to tolerate. Some varieties need shade, while all plants that have been protected from direct sun will be tender until hardened off by gradual exposure to sun light. Possible solutions are to give the plant more shade or move it to a more protected site.

After pruning rhododendrons, they normally show this sun scald because the newly exposed areas are tender.

Turning yellow and/or orange is also what leaves do when the plant is shedding older leaves. When the plant is not healthy, it sheds its older leaves sooner.