Hi Andrew. Sounds like it is the combination of heat and to much moisture.
Morning sun should be good. Sounds like you are fluctuating between to much water/rain and then not enough. Protect them from the rain and afternoon sun.
Twit should come along soon and have more thoughts on what you should do.
Meanwhile, can you post some photos so we can see what they are looking like?
Hi Andrew. Sounds like it is the combination of heat and to much moisture. 
