I've been to Guernsey a couple of times, both at Easter - but I have been to Jersey in October and had reasonable weather. To be honest the weather is similar to the south of England and equally unpredictable at that time of year.

We loved both islands, particularly Guernsey. There are some lovely beaches, scenic stretches of coastal path and pretty villages to explore. I'd recommend it and will certainly visit again myself. If you're looking for some reasonably priced accommodation, we stayed here.

http://www.peninsulahotelguernsey.com/