Do you know what the pH of your rain is? I know mine is fairly alkaline (which I find totally weird)... If you're convinced it's a pH problem from the rain you've been getting and you KNOW your rain is acidic (below, say, 6.0), you might want to erect some kind of tent over it to prevent a lot of that water from getting to your roots... But I'm also wondering about the heat... this, to me, doesn't really look like a pH problem - I think you'd see some nutrient deficiencies (calcium, phosphorus, maybe some potassium issues) as the pH would start to lock those nutrients out... and I don't see that kind of damage. So perhaps it's heat? And again, if you could rig up some kind of shade for the middle part of the day, it might help. The only OTHER thing I can think of is that the rain might have been pretty heavy and caused some stems to be bent/injured in some way? If you find that kind of damage, a gentle taping back into position could help enormously although it might be too late - but you could/should always try...
Good luck - looks to be a beautiful grow otherwise!