I've read that the the Hawaiian islands disrupted ocean swells in ways that Polynesians could detect even 1000+ miles away. In addition, the Hawaiian islands are huge and lush, and dumped a large amount of plant debris into the water, some of which Polynesian sailors would occasionally notice while at sea. I'm skeptical that those signs would have been noticable all the way from the Marquessas islands, but the Marquessas Polynesians were likely ranging 1000+ into the ocean themselves, which evidently was enough for them to deduce the existence of large islands in the general direction of Hawaii long before they discovered it. Evidently according to oral tradition, the discoverers of Hawaii arrived equipped with plants, animals and other gear to establish a new settlement- they knew the islands were there before anyone set foot on them.