I've heard that exposure to cooler temperatures can cause tomato flesh to break down. That's why you shouldn't store tomatoes in the refrigerator. Especially if cool temperatures are endured, you might take trouble to pick at first blush instead of fully red, and let them get red indoors. Really no reason to leave tomatoes on the vine until they are fully red.

But watering once a day sure sounds like a lot for the PNW. Why would you do that? The threat from that is more likely root rot than mushy tomatoes, though. If the soil is moist one finger deep, don't water.

It's a tough question to answer, and watering a lot can indeed help with that, but it's not the only cause. Nutrition has some role to play but I don't know which exact element is involved.

Once a day in soil is a lot, depends how raised you beds are also, but I'd switch to max once 2-3 days.

Thanks for your comments. They are in raised beds in full sun and the soil dries out quickly. The soil is amended compost and that worm casing blend. The lows now in the summer are 50' and above at night/morning, with 75-85' daytime temperatures. I will try watering every few days or so... weekly would kill them, as recommended in another posting. I have always had great plants and fruit, just some are mushy... especially the sweet 100s and smaller.

Don't water by the calendar. Water by when they need it. Check the soil at depth with your finger. Keeping the soil moist on the surface is a recipe for fungal infections. But I don't think overwatering is making mushy tomatoes. 50F is kinda cool for tomatoes, though.