What you have is a dry to wet problem tomatoes have. They are splitting since the skin dry's out with dry conditions and with a large amount of water they swell and split. Like a stretchmark gone bad.
Consitent watering is the key. As soon as you figure that out, hit me back. I always have splits as well. They are still edible, but if mine get to the moldy stage they become seed tomatoes.
Good luck in this heat it is very hard to keep it even.