In general, you should have good weather but there is always a chance you will get rain. On our last Mexican Riviera cruise we did have one or two days of heavy overcast.
One way to get an idea of what the weather will be like is to check weather.com a day before you leave and put in the port cities. Then you can get a 10 day forecast for each city. This will give you a good idea if you need rain gear or not.