Here are several previous discussions about splitting, its cause, and tips on preventing. Thought you might want to read through them for information.

Dave

Here is a link that might be useful: Splitting tomatoes discussions

Thank you digdirt. I did read through the discussions, and it was very helpful. I think I may be watering too much out of concern that with the high temps they would suffer. Will try laying off on the watering to see if that helps the rest of my tomatoes.