Why Do Tomatoes Split After Rain Even When the Soil Was Already Moist?

Several ripe tomatoes in my garden split after a heavy rain, even though I’d been watering the plants regularly and the soil didn’t seem especially dry beforehand. Some cracks run down from the stem, while others form rings around the top.

Is this mainly about a sudden change in how much water the fruit takes up, or can ripeness, variety, or uneven watering over previous days matter too? I’m trying to figure out what to watch for before the next stretch of wet weather.