The rot may be blossom end rot which will get better when the soul moisture levels out again. Other fungal rots can also affect plants. I suggest picking and discarding the affected fruit. If the weather will get back to normal the plants should be fine. It may be necessary to spray the foliage with a fungicide labeled for tomatoes a couple of time 10 days apart to get any foliage diseases under control. In fall when the cooler temps return the plants will start setting fruit again and you can get another crop out of them.
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