On average, the sun shines 358 days a year in the Bahamas. Because of the Gulf Stream, winters in the Bahamas are fairly mild, about 10 degrees F/5 degrees C warmer than in nearby Florida. The summers can be humid, rainy and warm (day temperatures range low 80s to low 90s F/28-33 C), but are moderated by trade winds. High season is from November to mid-April, when the weather is generally good.
Hurricane season is June-November, and most rain falls at that time, although rain and thunderstorms generally pass through quickly.
There really is no bad time to go, but take along at least a sweater during the winter. Average day temperatures in fall and spring are in the 70s-80s F/23-32 C, with nights in the 60s F/15-22 C. Winter temperatures can be about 10 degrees F/5 degrees C cooler.