What's happening to my wife's tomatoes?

Southern Ontario, Canada. It has been crazy hot and humid - 33C plus humidity.

Do we need more water? Less? This is happening to about 1/3 of the tomatoes and they are not resting on the ground.

Edit: thanks everyone. She's going to start with a bit of lime and some more attention to how much she's watering.

She may even create a lemmy account now that she's seen how many helpful fellow gardeners around here, so win-win!

Thanks again