Quite rare but annual. There have been a few reports by the local sea watch, coming all from a particular magician of a birder. The reports were of birds out over the open ocean and during migration so it’s unlikely this is the same individual.
At this point I could add to the discussion, for what it’s worth, at a great distance on a rocking boat, it immediately and continuously rejected the notion of northern gannet to me. I was the only person who saw the bird. The bold contrast pattern suggested by all of the photos consistently was evident to me in the field although the distance made it difficult to precisely ascertain the pattern. It did look clean cut as far as I could tell.