We've been to Ocho Rios the last 3 years, always in March and out of that total of 24 days, I think it rained a total of 20 minutes during the day. There was one night last year that it rained for a while.
Just got back from CSS on March 1st. We were there for 8 days and it rained for 3 hours (11AM to 2PM) one day, that was all. Besides that, the weather was gorgeous. An occasional small cloud came through and dropped a couple of rain drops, then moved away.