The Mexican RIviera is a lot warmer than here in the US. Further south means higher temp's. You may get some rain, but winter is actually more pleasant weather there than summer in my book. We've been to Mazatlan in summer when it was 114@ and 90% humidity. Go in winter!
And, as said, go for a longer trip if you can, sway 7 day cruise. Otherwise, you will only see Ensenada, which is probably the least exciting place I have ever been to in Mexico. Still, better than no vacation at all.