The weather during high season from mid-December to mid-April is perfect for hanging out on 7 Mile Beach: It's usually dry, and the cooling trade winds from the northeast moderate typically high temperatures. Sometimes a few days will be windy and cloudy, but these periods of inclement weather usually come and go quickly.
Weather-wise, the best month to visit the Cayman Islands is April, which boasts perfect warm weather before the heat of summer hits in May. In spite of the heat, many Europeans prefer a summer visit. As one visitor who hails from Yorkshire told us, "After a cold winter in the north of England, I've come just for the heat."
Rainy season is from late May until late November. However, it does not rain every day. Often the showers are short (albeit intense) bursts that are followed by clear skies and plenty of sun.
Even though the Cayman Islands are one of the world's leading scuba-diving destinations, divers often avoid the islands in August and September, when tropical storms can churn the waters. However, because the islands have so many dive sites, you can almost always find places to dive, even in August and September.
A Mighty Wind: Hurricanes on the Cayman Islands -- The curse of Cayman weather -- the hurricane season -- lasts officially from June 1 to November 30. But there's no cause for panic: Satellite forecasts give enough warning that safety precautions can be taken if a storm strikes during your visit.
Info from http://www.frommers.com/destinations/cayman-islands/729787