With the widely fluctuating amounts of rainfall, blossom end rot is definitely a possibility. The best solution is to mulch tomato plants to help even out the moisture supply, and help keep the roots cooler. This problem is caused by uneven calcium amounts in the plant. Addition of lime when you see the problem usually isn't as effective as evening out the moisture flow for the plant by mulching. Any material will do (grass clippings, straw, commercial mulch, etc.) with two inches being adequate and four inches being better.