January to March: hottest and wettest, 30°C+ and humid. Cyclone season; most years pass without one, but if one comes it shuts the island for two or three days. Waterfalls at full flow. Lowest hotel prices outside the holidays.
April and May: the best months. Still warm, rain easing, sea still 27°C, everything green, crowds gone. If you can pick, pick these.
June to August: winter. 24°C by day, cooler nights, dry. Trade wind steady on the east and south, which brings kitesurfers and keeps the east coast beaches empty. Prime hiking. Sea at 23°C, still swimmable.
September and October: warming up, still dry, wind easing. Good all round; October is the second-best month after May.
November and December: hot again, sea warming, occasional short storms. December is peak price for the holidays; November is not.