The temperatures are regulated year round by constant trade winds blowing east to west off of the Atlantic. Typically daytime temps in the winter are around 75 to 80 F and in the summer are around 85 to 90 F. At night in the winter you may want a light jacket, but only occasionally.
In the heat of summer 90 degrees is not too bad, especially with a constant 20-mph breeze – certainly not as hot as Florida in the summer. During the day we keep the main doors and windows open and let the breeze cool the house and at night we close up and turn on the bedroom air conditioner. Make sure your rental house has bedroom air conditioning – some on the island don’t!
Rainfall on the island is very sparse which is great if you are on vacation, not so great if you are depending on the rain for house and watering needs.