You can book as early as 330 days out, on some carriers...depending on the carrier you might get your best airfare now. I could have gotten flights for $226 pp in August for our March trip(on United), on SWA I got tickets(on Thurs) for my friend(going the same time) for $280 pp(but it was non-stops/she travels with 3 young children alone).
You never know But SWA traditionally does a sale of tickets around July 1-4 that I think includes dates in August. You have to weigh the variables: seating, non-stop vs stops, price, planning window, and the cost of second choice. If you are at all close enough to poss drive- I think I would wait for the SWA summer sale, or buy a refundable ticket on any airline you like.