Ryanair offer travel insurance policies as an add on to a flight booking, or they can also be purchased as stand-alone products. Ryanair travel insurance is offered in two levels, so you can choose the option that's right for you and your wallet.
Jamaica's rainy season coincides with ours here in Florida (I am in the Tampa area) for the most part. We have anywhere from 30-50% chance of rain daily until hurricane season is over. I didn't mean you have rain every day, all day from May to December in Jamaica, but I assume it is a lot like here in Florida.
In the mountains, the thermometer can dip to 40 degrees Fahrenheit (4 degrees Celsius). The rainiest weather in Jamaica occurs in May and June and again in October and November and can sometimes extend into December. While the average annual rainfall is 50.7 inches, accumulation varies dramatically across the island.