I'd have to go along with RainbowGardener. Be a good idea to first check for the borer. As he said they can do a lot of damage almost overnight.
I'm not sure sure this would be the reason for the tomatoes issues.
I guess we assume you have been keeping the crops properly.
I live in GA, and we have 20 days in a row between 95 & 100 (a few days over) and had no rain. I watered me garden about every three days with a sprinkler for about 4 hours each time.
All my plants are doing wonderful. I only have 5 tomato plants, but I picked almost 7 gallons of tomatoes this morning.
As you said it's been very hot there, and no doubt the ground is dry (not just on top but deep down also)
The reason I mention this is a few weeks ago Day dug up a spot in his garden and it was dry much deeper than he assumed, and so he went to watering more and longer to get some water back down into the ground deeper to help the crops.
If the other crops are all doing well... I'd guess it's the borers, but if anything else looks wilted or is drooping, I'd give them more water.
OH.. I almost forgot. I assume you know WHEN you water makes a difference. I Never water (overhead) during the day. If the plants are hot, and you spray in water in the daytime; it can damage the plants. I water mine just before sundown when they are much cooler. Dad goes a step further, every day just before dark he sprays all his plants for just a little while so it will cool them off... and not take well into the middle of the night for them to cool of 'naturally'. According to him this helps stress the plants less. I can't say that it don't work because he always has a wonderful garden.