Gardening question, do any jellies have tips to stop splitting in Supersweet 100 cherry tomatoes after a heavy rain?

Not much you can do, it is the temp. fluctuation and humidity that causes them to rot/split.
I just got ONE Brandywine heirloom yesterday that was starting to rot/split on the bottom. I had to cut about ⅓rd of it off but it was still deeelicious!
My cherry tomatoes are doing great, just collected a bowl full tonight, they seem resisitant to the funky weather but the heirlooms are so sensitive.

I have a Brandywine, a German heirloom, and one other heirloom coming plus the cherries. They’ve been so good so far.

Would a large umbrella help? It would keep them from getting too much direct rain in the soil immediately around the roots. That extra water may be making the skins split.

You need to spray your tomatoes with water on a regular basis, to get them used to the rain. It has obviously been hot and dry where you are, and then when the rain comes, it shocks the tomatoes and makes them split.