For accurate weather information, you can take a look at worldweather.wmo.int to get a good idea of what the weather in Cuba will be like.
One thing you will want to be aware of is that the temperature rarely gets below 70 degress Fahrenheit, even during the wee hours of the morning. If you plan on traveling to Cuba during the summer, July, August and September can be muggy and fairly hot!
As far as clothing goes, you can be comfortable and fit in wearing most typical outfits. Shorts, tank tops, bathing suits - all are fine. We recommend you have several outfits that are light and ready for warm days, as well as a few nicer outfits if you plan on going out at night. You might also consider a cardigan or sweater if there is a night where it gets a bit cooler out.