There are some insect pests of carrot roots like the carrot rust fly but if they were the problem, you should see the little maggots feeding in the carrot tissue. I suspect that this damage is actually caused by a root disease that cleared itself up when the weather got dryer but the damage was left behind. I have seen this same kind of damage in my own carrots. Did you notice any carrots that had a soft rot, usually near the top of the carrot? I think this is the same thing but a mild case. The splits in the carrot result in inconsistent moisture conditions, some rain after a longer period of dry weather causes the carrot to start growing again, often causing it to crack.