To add to what Marty said, San Pedro enjoys prevailing breezes from the water most of the year, though the direction shifts somewhat and the strength of the wind changes over the year. Really, these prevailing winds are what make the island so pleasant, as they cool things down and keep the bugs away. In late summer, especially August and September, there are usually calm periods when the breezes die down, and THEN it really gets hot, humid and buggy.
January through April is the time the winds are strongest (except of course during hurricanes), and they can be up to 15 to 20 knots on many days. Sometimes they are strong enough to make snorkeling and fishing trips difficult or inadvisable, but just wait a day or two and you will have some nice weather for what you want to do.
March is high season throughout the Caribbean because it's when much of the U.S.and Canada is freezing.
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