It can be hit/miss for the Mexican Riviera in October. It's the end of the rainy season and mother nature may not be done with it by then. I've seen sunny, beautiful days....and days with clouds, rain and thunderstorms too. I was also down in Puerto Vallarta in mid October and there were, not one, but TWO tropical storms spinning right off the coast, sending wind/rain accross the bay onto the coast. I def would not have wished to be on a cruise during that time. But odds are, the weather will be fine!