My son and I are planning a pelagic bird trip out of Hatteras in Aug.
I’ve been to Hatteras once. One thing I didn’t expect at the lighthouse, deer.
Water temps drop as you go up, in summer rarely reaching the mid-seventies north of Rodanthe, Waves and Salvo. Further north toward Currituck, Corolla and Carova, summer water temps in the sixties are not uncommon. Makes for a lot of variety. Certain times of year it's even like the marine layer rolling in and out, that you see on the central and northern coast of CA. Always loved that.
If you're going to be renting a house for more than a few days, you'll want to stop into the Food Lion in Avon. Prices are normal there, not island prices. Gas up before you cross the bridge over the Alligator River if you're driving in via that route, or before the ferry if that route. Island prices are expensive.
It's a beautiful, wild place, outside the few towns and tourist areas. Nature is on full display, wind, water and blowing sand. I love it. If you're into shore birds at all, Pea Island has a reputation of being good for that sort of birding.
Have a great trip.