Tomato cracking: Yes, you can prevent it

Salvage a cracked tomato by cutting around the bad part.

It's so frustrating!  Tending the plants for months and then, just as they ripen, finding cracks that seems to have developed overnight. Why, oh why, does it happen? Because the plant isn't getting a consistent source of moisture. The soil is too dry and then too wet.  You can prevent it by simply watering on a consistent basis. More when it's dry. Less when it rains. Easy, hunh?

Here's a more detailed explanation from the North Carolina State University Extension Service:

 SPLITTING AND CRACKING

Side splitting and cracking up are terms you want to hear in reference to a joke you just made, not about your tomatoes. Heavy rain, especially when preceded by dry weather, is the leading cause of fruit cracking and splitting in tomatoes. This type of damage is most likely to occur as tomatoes begin to ripen and you are anxiously anticipating harvest, though green fruit can be effected as well.

Cracking and splitting occur when rapid changes in soil moisture levels cause fruits to expand quicker than the tomato skin can grow. There are two different patterns this damage may take. Vertical splits along the sides of fruits are known as radial cracking and are the most serious. This pattern of splitting commonly occurs during hot, humid weather. Cracking that occurs in a circular pattern at the top of tomato fruits, ringing the stem end, is known as concentric cracking. When cracking of either type occurs in green tomatoes, fruits are likely to rot before they fully ripen if left on the vine.Tomatoes with radial cracks will rot quickly if left on the vine.

With both radial and concentric cracking, your best option is to harvest fruits immediately, before they begin to rot. These fruits are edible and can be allowed to finish ripening indoors, though any fruit that develops a sour smell or begins to ooze should go straight to the compost pile. Fruits that ripen off the vine, as well as those that ripen on the vine during cloudy, rainy weather will be less flavorful than those that mature fully on the plant during sunny weather.