Why are my tomatoes rotting before ready to pick?
First year planting them. Planted June 1st after risk of frost, but planted them way too close together - first timers mistake. Vines grew to about 4 1/2 feet tall. I've watered them at the base only keeping soil moist in dry weather, and fertilized 1x weekly (once tomatoes started to bud). They get full sun. We've had a lot of rain in the past weeks, and very hot humid weather.
They are starting to rot on the vine - before they are even fully ripened and ready to pick. Vines are unaffected, no holes or apparent insect infestation. I had to cut the vines back recently because I could hardly get to the tomatoes - they were that dense.
Why are my tomatoes rotting? Is this a disease, not enough air circulation, or something else?
I didn't plant any hybrids, and none are cherry/roma tomatoes. Cultivars are tomato boy(?), Brandywine, and Beefsteak.