One day you see your tomatoes are looking healthy and the next day you come outside and your tomatoes are split/cracked open. This is not an uncommon occurrence especially after a hard rain. The skin of the tomato is tender and with inconsistent watering, it will easily split. This often happens when the tomatoes were not receiving large amounts of water, then suddenly receive a large volume at once. The skin on the tomato cannot grow fast enough to make room for the water, causing it to rip open. Inconsistency with watering will cause your tomatoes to absorb water faster than the outside skin can grow to hold. While a split tomato might not be as aesthetically appealing as a non-split one, it is ok to still eat as long as there are no signs of pests, mold, or rotting. You should pick split tomatoes immediately as they will attract more pests and potentially mold as they stay on the vine. The split area can always be cut/removed before consumption.
To help prevent cracking in tomatoes, try to consistently water them once fruit development starts. This is especially important in cases of long droughts and dry weather. Ensuring consistent water during these periods will help reduce the chance of cracking from heavy rainfall. Water your plants deeply, this means watering so at least the top 6-8 inches of soil receive water. Tomatoes that are close to ripen are more susceptible to splitting. If you are expecting a hard rainfall or fear your tomatoes might crack, remove almost ready tomatoes and allow them to ripen off the vine. A final action to take is using mulch on your tomatoes. Mulch will help retain moisture to ensure a more consistent watering as well.