Don't know where your "tropical" experience is from, but you may find the air and water about the same in NC in early August. I dived off of Morehead City in May '03 and October '03, wearing a 3 mil over a 1 mil, and got chilled only on the last day of the Oct trip.
But you're more experienced than me, burning less air and calories, more easily chilled. I did 3 dives this weekend in 72oF water, hot air for Surf Int, and finally started getting chilled at the last. While I'd dive NC in early Aug in a 3 mil alone, you may want more. Your heavy vest & hood should make it fine then.
Oh, and do wear the hood. On the last dive there, I G-strided into a sea nettle. Had a scab on my forehead for a month. Rare, but possible.