Tomatoes split because of a sudden influx of water sometimes due to a rain burst or if you flooded them with water. This normally happens when the tomatoes are near ripe. The sudden deluge caused the tomatoes to swell up, causing the skin to split. The tomatoes are still fine to eat with a split skin, but should be eaten immediately.

Be careful not to over water the tomatoes. One good watering per week is plenty with a thick layer of mulch. Also, too much water ruins the flavor - creating a watery, bland tasting tomato.

Where in the world do you garden, Bob? In areas with hot summers, in containers, tomatoes may need watering twice a day, as we do here in the desert. Also, if you went away for a week or two, and left the watering to someone else, the sudden influx when you came back may be responsible.