The rainy season is Sept.-Nov. with a fair amount of variability. Sometimes very little, sometimes way too much rain. The rest of the time, the wind is predominantly from the east (over the island). Access to sites varies little, although more people are there in the winter than the summer. Viz is generally the same year 'round, varying with the change in wind direction. Although wind is normally from the east, it can come from the northwest which can really, really drop the vis. Nearby tropical storms or hurricanes will cause wind to come from the north-northwest, wreaking havoc with viz and shoreline structures. They are not too common. Winter and early spring is the high season, but personally, I like the summer just as well. Less expensive, fewer people both at dive sites and restaurants and you'll probably get a better quality rental truck.