We have festivals in May, like the Moor and Coast Festival in Whitby on the first weekend in May (including a National Holiday on the Monday). That might be useful if you're planning to go through Whitby and Robin Hood's Bay. The weather will be like it always is - variable. Whitby seems to have its own weather - it's often doing different things to the rest of the country! But plenty of people camp at the festival, if that's a measure of the weather at that time. Ear-muffs should not been required! And the daffodils have been out for ages here.