It appears you bought mature plants,if you only planted this year and they're this large. The cause of the red leaves dropping off will not have been wet and wind - red leaves on this plant are new growth, so they will have fallen because of insufficient water at the roots. Plants this size will have had a large rootball, and in order to soak all the roots, a lot of rain is needed. Suggest you keep them well watered when the rain stops, couple of gallons each plant per week as a minimum, more if its hot, until next winter.
The plants are obviously coming into flower - I'd be inclined to wait for the flowers to fade and then do any pruning you want to do. Bear in mind that mature plants have much more difficulty settling into a new situation, and require much more care and attention to feeding and watering.

Thanks Bamboo.

Yes they are mature plants and although I have watered them regularly it's obviously not been enough so I will give them more water and on a regular basis and may give them a feed soon as the last feed was when they were planted at the end of Jan. The man that planted them for us mixed some Vitax Q4 in with the compost so I will use some more of that.

Is there an easy way to tell when they have been overwatered?

Well obviously at the moment they appear to be getting enough because there's new growth and flowers are forming. But once the weather's recovered and stopped raining all the time, that's when you need to water. Remember the rules though - water a lot occasionally, NOT little and often. Give them a good soaking of a couple of gallons a week in dry weather, as I said, and in particular, when the weather is hot, they may need more. You can't overwater plants in open ground, unless there's a solid layer of something beneath the soil and drainage is poor, and you'd know because you'd be splashing when you went to water.