I live near Atlanta (hot & humid). After 14 years we have no problem with our solid wood Wood Harbor doors. I think it is because they are made with different layers with poplar being the top veneer. If they were solid pine or alder they would be more susceptible to warping.

Rarely do you see solid wood doors anymore, so the questions becomes if you are painting or staining your doors. If you are staining then a veneered door is your ultimate choice with an engineered particle core like Barbara is mentioning. If you are painting, then here are some reasons why MDF is used in residences and hotels across the nation. 1) Finishes fantastically - since there is no "grain" to MDF, you get a extremely smooth finish. 2) Sound control - since MDF is quite dense, you get a greater sound barrier between rooms, 3) Environmentally sound - MDF is typically pre-consumer recycled material. 4) Extended warranty - in our case we warranty the doors for life, a rarity for real wood doors.

By the way - excellent choice to go with an 8 ft tall door, it'll make such a difference over the 6'8" and 7'0" tall that most people opt for. The 4 panel look would work well in your vision, and take a look at using flat panels and a "shaker" profile vs raised panels and an ogee sticking. Also you'll end up choosing between 1-3/8" and 1-3/4" thick doors - I'd opt for the thicker door since you are doing the 8'0 tall doors.

Best of luck!, and I'm sure you'll make the best choice. Kudos for thinking about this BEFORE the doors are installed :-)