Blossom end rot or the end of tomatoes get a scabby
end,mean either toooo much water - probably not; 
not enough water - very likely in most gardens; or
too hot  yes;  or too cold;  yes, the last three weeks. 
Solutions:  add mulch to the soil or use drip hoses;
add lime to the soil, rototill lime (rate of 50 pound
per 1000 sq feet).