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.
Regardless of when you visit, the tropical climate and warm temperatures of Jamaica essentially guarantee beautiful weather during your vacation. Average temperatures in Jamaica range between 80 degrees Fahrenheit and 90 degrees Fahrenheit, with July and August being the hottest months and February the coolest. Temperatures in Jamaica generally vary approximately 10 degrees from summer to winter. Nevertheless, you should be prepared for winter in Jamaica to be slightly cooler, especially at the higher altitudes. In the mountains, the thermometer can dip to 40 degrees Fahrenheit (4 degrees Celsius).