No seasonality here.  You can SCUBA anywhere here all year long.  The turtles, rays, eels, white tipped reef sharks and octopus are abundant right near shore.   The sea life love the warm water here and there are dives for every level of free diver as most dives are not more than 35-30' and the visibility is between 75-100' if you can get there in the early morning.   Splurge for a boat as all the reefs and turtles are off shore about 1/4 mile.