Zosh, you don't say when your going. We have been on the Monarch twice, once in December and another this past October. 7 other times on various Carnival ships. It is chilly in the evenings and it can be cold in San Diego and Catalina. On our October trip, it was coldest in Ensenada. Bathing suits are a must no matter what the weather. If your sailing in the spring or summer you will be fine with light clothing. Any other time hope for the best and prepare for the worst. Its best to have and not need it then the other way around.