You will traveling in summer, so the surf won't be to heavy. Waimea Canyon and the Kalalau Lookout are a must see. If you like hiking, the Kalalau trail on the other side of the island goes along the Napali Coast. it is a difficult but spectacular hike up and down the coast. It is only 2 miles to Hanakapii Beach. It is 13 miles to Kalalau Beach. Too far for a day hike. The currents can be bad, so if the surf is up, do not go in. We went in January a few years ago, and the trail was closed due to bad weather. There are other beaches and caves to explore if the trail is closed or you decide not to go.