I've sailed the Mexican Riviera twice in the last three years and both times the seas were relatively calm.
Last February the seas were a bit rough (5 - 7') for the first night out of San Diego but as we went south the seas became very calm.
It all depends on what storms may be in the Pacific and it really is impossible to predict. This time of the year there are (Usually) less storms so the seas are more calm.
Have a great cruise and take your Dramamine or Bodine. Just in case.