This is a bird that is difficult to photograph. They will appear out of no where and mix in with other storm-petrels. They are slightly larger but certainly longer winged than the ever present Wilson's SP and they have a unique flight style frequently compared to a Nighthawk. The sightings are usually fairly quick as they do not stay behind boats like other SPs will.
This one was photographed on a Patteson pelagic out of Hatteras. Note the forked tail and long wings.