Too much water after they had already started to ripen is the usual cause. To avoid the cracking try to pick the fruit when they first start to break color.

They are on a drip system. 3x a week. No rain. I live in CA and it's still fairly hot out.

It appears they went thru a sudden growth spurt usually caused by a sudden increase in the amount of water they received. Maybe a leak or increase in your drip system?

I'd like to point out that while they may not be pretty, I bet these are still might tasty.

+1

Those is the pics don't look bad at all.

Pick them at first blush to help avoid this.

Some varieties are more prone to cracking than others.

It's not a bad idea to pick at first blush.

It prevents you from forgetting about them and a snail coming along and dining out.

Also, you can then ripen them in the shade (not on a sunny window sill). Ripening them in the sun changes their taste to being LESS tasty.

The following is from:

http://www.weeklytimesnow.com.au/country-living/gardening/peter-cundall-reveals-the-secret-to-tasty-tomatoes/story-fnkeranf-1226850205940 

IT’S NO accident that the best-tasting tomatoes are always well hidden, deep within the foliage of plants. Being out of the sun means they ripen under cooler conditions and therefore develop maximum flavours.

It’s hard to believe that direct sunlight is the great destroyer of tomato taste, but it is true. Some varieties — especially those that simply form low, spreading bushes — usually have trusses totally exposed to strong sunlight.

They not only lose flavour, but the most exposed fruit usually develop a form of scalding. We see this as bleached, shrivelled areas on the shoulders and these disfigured, sun-blasted tomatoes have to be discarded.

Whenever overexposed tomatoes are observed, I simply tear off large rhubarb or cabbage leaves and drape them over the top to provide a protective shield. They dry off to a crisp after a couple of days, but can still be left in position to provide valuable protection.

Oddly enough, those tomato varieties that tolerate ripening in full, strong sunlight are those that produce clusters of cherry-sized fruit, such as “Red Cherry” or “Sweet Bite”.

It's worthwhile reading the remainder of that article:

I always heavily mulch our tomato plants using any kind of straw or spoiled hay. It is well-tucked in close to the stems and kept moist. This encourages stem roots to emerge and if the mulch has been enriched with manure, the tomato yields can be almost doubled.

Mulches also keep soil consistently moist and this is vitally important when tomato plants are producing plenty of fruit. If the soil is allowed to dry out, tomato plants immediately show distress by beginning to wilt. Fortunately a good watering in the nick of time causes those drooping leaves to rapidly pick up.

However, it is the fruit that suffers most when the supply of moisture to the roots is checked. We see it as black, unsightly scabs that form on the bases of the tomatoes.

While the actual cause of “blossom end rot” is lack of calcium, the ultimate reason is because lack of water stops the plants from taking it up.

Another common problem with some tomato varieties is splitting or cracking, usually in a kind of rough, broken circle around stalks. “Black Krim” is particularly vulnerable for some reason.

Once again the cause is an inconsistent water supply. When soil close to the roots starts to dry off, the tomatoes briefly stop swelling. Consequently the skins lose elasticity and when watering resumes, these splits appear.

At the moment I’m busily going through our tomato plants checking for these disorders, I’m also snipping off all lower leaves.

These are the oldest leaves and are usually curled and yellowish because they are almost dead.

As tomato trusses are harvested — usually from the base of the plants upwards — I keep cutting off these dying leaves. So over the harvesting period, the lower branches become increasingly bare — which is no big deal. In fact this helps prevent diseases while removing hiding places for pests, especially green vegetable bugs.

These “stink” or “shield” bugs suck juice from the tomatoes and in doing so taint flavour and spoil the appearance. They leave countless yellow marks in the skins where they have been feeding.

Vegetable bugs also attack beans, silverbeet, brassicas and pumpkins. Never make the mistake of squashing them with fingers because the sickening smell tends to cling for days.

Good control can be achieved by pouring a small amount of water and a little mower fuel into a bucket and shaking any infested branches over it. The bugs fall in and the fuel kills them within minutes.

The same treatment can be used to control harlequin bugs.

I'd eat'em anyway.

Best tasting are well hidden (sorry, new format won't let me copy/paste!) Oh yeah! My Purple Cherokes are VERY well hidden! DH doesn't tend to bend over much and I go out and find a BUNCH that he has missed! Even the red ones sometimes get missed cause he doesn't look from different angles as I do! Nancy

There are other ways to control cracked and otherwise blemished fruits other than picking prematurely. In my high tunnels the incidence of fruit cracking is very low and I allow fruits to vine ripen. Some research trials show improvement in fruit quality by applying a shade cloth over plants. Fall weather which in most areas has cooler nights and dew point be reached frequently is a much greater factor in fruit cracking than soil moisture fluctuations. Keep moisture off the fruits and fruits will be more blemish free.

Forgot about the cool nites. Guess that could be the prob here?

Definitely caused by an increased amount of water, watch out cause Gumby would tell you this was blossom end rot /ridicule

I'm gonna guess that FastInk is twui and prob having troubles at home. Apparently s/he doesn't read well either. Too bad, soo sad.

Lol just picking at you gumby, I mean after all you said that over watering will cause blossom end rot in another thread, funny how nobody ever experiences tomato cracking and blossom end rot on the same plant tho..

<Lol just picking at you gumby, I mean after all you said that over
watering will cause blossom end rot in another thread, funny how nobody
ever experiences tomato cracking and blossom end rot on the same plant
tho..>

Does NOT sound like anything Gumby would ever say. But I'm gonna say I doubt that you can post a link to where you think you saw that.

Gumby is gonna say that if you do NOT give your tomatoes enuff water
while they are growing and then experience a rainstorm where & when
the plants can take up more water than they are getting from you =
cracking and/or splitting tomatoes will result. It really is that
simple.

So cracking and/or splitting tomatoes and BER are not
from overwatering but from not providing adequate water on a consistent
basis.

During the heat of summer I water my tomatoes daily sometimes 2x if they need it.

Gumby this is like the third time I have seen you refer to yourself in the third person. Are you serious or are you forgetting which account you are posting from?

Peter, Gumby is being funny. Read further up. Fastink quoted what he thought Gumby would say on the subject. All in fun :)

Linda

<Peter (6b SE NY) said:

Gumby
this is like the third time I have seen you refer to yourself in the
third person. Are you serious or are you forgetting which account you
are posting from?>

Now Gumby is wondering if Fastink is really Peter? Why else would Peter care or know anything about having a different account? Re:<But I'm gonna say I doubt that you can post a link to where you think you saw that.>

Peter is one who thinks you should only water tomatoes only once a week to avoid cracking.

Gumby thinks Peter needs to learn how to worry about Peter and stop worrying about anyone but Peter.

Regis said Gumby is gonna be alright <smile>