The wet season is very wet and runs from August to December. It can rain for days on end. If you bring an umbrella, make sure it is the type that opens to form a complete sphere around you, because the rain falls sideways. Honestly, go to a camping store and get a waterproof cover for your backpack, a light waterproof jacket and a shamie. You will be the envy of everyone. Another thing to consider is the mosquitoes. The breeding ground for mosquitoes is standing water, and there will be a lot of it. Invest in a mesh tent for your bed and screens for your windows (only applicable if living off campus). Want to know a fun trick? Instead of a mesh net, get a standing oscillating fan. If you go to sleep with it by your head, the mosquitos get sucked into the back of it and murdered. You get to wake up the next morning with a pile of them on the ground. Good times.
There is little rain in the dry season which runs from January till June. It is the best time to be on the island and enjoy everything that it has to offer. Go to the beach, learn to kite surf, bring your surf board, or rent a jet ski. Head to the capital and learn how to haggle in the market. Most of all, remember to get a tan so that people believe you when you say that you go to school on a tropical island.