We were in Negril in April 2009 and Ocho Rios (Tower Isle) in April 2011. We traveled in early/mid April both times. Weather was beautiful - not one day were any water sports cancelled at either place. We got married this past April. Here is a link to our slideshow - As you can tell by the photos, the day ( and week) were perfect
We usually go in mid April when the rates drop. We've been on both sides on the island (Negril & Ocho) 4 time each and we always had good weather and never saw water sports shut down due to weather. Maybe we just got lucky but I think the weather in April is as good as any other month. You may get a shower or two throughout the week but they are short and sweet.
The temperature in Jamaica is pretty consistent all year; 80's during the day and 70's in the evenings no matter which month you choose to go.
We were just at CSA 4/22-4/30 and had absolute wonderful weather---full sun very few clouds every day. We had 1 shower in the early afternoon one day for an hour maybe----we just ventured over to the beach bar and waited it out. No worries, and we can't wait to go back. Looking at going back next year in April
We went 4/22-5/2 and experienced 2 days in a row where there was a pretty strong downpour for at least an hour or two around lunchtime, and some scattered brief showers a few other days. Most of the time the weather was sunny and it wasn't ever really windy that I recall.