Hawaii surf forecast

Hawaii sits in open ocean with nothing upstream of it, which is why it receives swell more cleanly than almost anywhere else on earth. North Pacific storms tracking between Japan and the Aleutians send groundswell south with thousands of miles of unobstructed water to organise in, and it arrives at reefs that rise from deep water almost vertically.

That bathymetry is the second half of the story. There is no gradual continental shelf to bleed energy off — swell goes from deep ocean to shallow reef in a very short distance, which is why Hawaiian waves break with a violence that the same offshore height produces nowhere else.