I was in Ireland in June 2010- but there was very little rain when I was there. It was not mainly for cycling, but I rented a bike in Dingle and rode around Slea Head on the Dingle peninsula, and borrowed a Dahon folding bike from my friends in Clare. There is a designated cycling route around West Clare- I saw a big display showing the routes when I went to Kilfenora. I also saw a group doing a climb across from Dingle back toward Kerry.
It was just a a bit unsettling for a while riding on the left side of the road, but I eventually got used to it.
It's a beautiful country, and I hope you will get to enjoy some of the incredible traditional music while you're there.
Where is your tour going to be?
2016 Specialized Ruby Comp disc - Ruby Expert ti 155
2010 Surly Long Haul Trucker - Jett 143