Also, if your DPS can't survive the lightning phase and they're far away from your healers tell them they need to just stick in an area with healers. There's no excuse for going and dying to dps as dead DPS is no DPS. The enrage timer on this fight is not tight at all, our guild typically kills him after the second storm and we probably have a similar iLVL as you (9/16 last tier). They honestly can't just say well I'm gonna sit in a place so I can DPS just heal me, if I die well then that's your fault. Also I looked at your logs and your two melee dps are a windwalker monk and an enhancement shaman. I don't know much about a windwalker monk but if your enhancement shaman hits his damage reduction cooldown, he should be able to live through the storm with very little healing as long as he doesn't get hit by orbs. You could also sit one healed with the melee and tank to heal them that way.
Just in summary, this fight can be done with some mistakes but things in your logs like anything that ends with conduction, or static wound on people who are not tanks if minimized could make this fight a lot easier to heal.