By the way, I never water my tomatoes overhead, with the spray hitting the fruit or most of the leaves.   I water around the base of the plant with a hand-held hose and sprinkler or use a soaker hose.
However, I live in the Willamette Valley of Oregon, and we do tend to get rain frequently in the early fall, even though tomatoes may continue to grow and ripen through October or beyond (depending on the year), and, yes, when a tomato that's been soaking up the sun for weeks gets rained on, it tends to split.   That's why there are special varieties for this region that are developed not to split in the rain.