Its driest here (statistically) between April and June. But even during this period there can be wet spells and it can be cold particularly if its dry and sunny during the day the temperature will plummet at night best book a B&B (near a pub) or Hotel rather than camp. Frosts in April are not uncommon. If you can, the best option is to see if there is a stable high coming in, in May or June and go for it (it was great this year in June it got up to 30+ centigrade which is very rare) and not much rain from February until now. I've been doing "look for high pressure and go for it", for years for trips to Scotland (though it's harder to get accomodation in North West Scotland at short notice now since the NC500!) September and October here can be wet and windy as can February March. It's generally more Stormy around the equinox's than at other times of the year. That said we are a smallish Island at the edge of the Atlantic so if you don't like the weather...........just wait a minuteDid it earlier this year, went from Cairnryan to Belfast, did the Titanic museum which I found an excellent experience.
Did an anti-clockwise route using routes i copied from the official guide onto basecamp, took two weeks in all with a mixture of camping and air b&b saw an awful lot of rain which was the main turn off for me and if I’m honest not somewhere I’d be in a hurry to return to any time soon.
.It can create its own drama mind
"Knockalla" Co.Donegal February

Not least (and this is a very poor excuse) the French are very good at putting signs on their many rivers.