For more details on temperature and stuff like that you can check any search engine weather feature nevertheless,

Rainy months are generally end of April -May and end of Sep -October

of course you all know there is the chance of a storm during the hurricane season, which peaks august to october or  there around

Its always warm/hot but cooler from Dec to April.  This is the better time for outdoor activities

April is easter time and the culmination of Carnival season, so if you are planning to go to ocho rios easter weekend book early as many locals flock there for the long weekend, some to relax and others to attend one or more of the carnival events: Beach Jouvert on saturday at James Bond beach in Oracabessa which has live bands(soca music), water paints (so dont wear your nice beach wear) and open bar. Chukka cove on sunday; live bands also but no paint.

You also have to book early if you are travelling during these periods: Heroes weekend in Ocho rios in mid October; the Jazz Festival in Montego Bay near the end of february and Emancipation and Independence weekend end of july/first week of august in Negril