Map from Google - Barbados

Barbados, the easternmost of the West Indies, has a tropical climate, hot and humid all year round, just cooler and therefore more pleasant from December to April, and a bit more hot and muggy from May to October. Anyway, the heat is tempered by the breezes.
The average temperature does not vary much throughout the year: from December to April, lows are around 70/72 °F, and highs around 82/86 °F, while from May to October, lows are around 73/75 °F and highs around 86/88 °F.
Here are the average temperatures of Bridgetown.
Average temperatures - Bridgetown
Min (°F)707070727375737373737372
Max (°F)828486868888868886868684

Along the coast the annual rainfall amounts to 47/55 inches, while it's slightly more abundant in inland areas (though not by much, because there are no high mountains that could force air masses to rise). In the capital Bridgetown, more than 4 inches of rain per month fall from June to November; the wettest period runs from September to November, with around 6.7/7.1 inches of rain per month, while the driest runs from February to April, with 1.4/2 inches.
Here is the average precipitation.
Average precipitation - Bridgetown
Prec. (in)

The rains, however, are quite irregular from month to month, which means that even in the rainy season, the weather may be good for entire weeks. The rains in Barbados occur especially in the form of downpour or thunderstorm, and therefore do not reduce too much the sunshine hours, which remain acceptable throughout the year, except when the island is reached by tropical storms and hurricanes, which can bring widespread cloudiness for entire days. Hurricanes may hit the country from June to November, but are most likely from August to October, as happens in general in the Caribbean.


For swimming, the sea is warm enough all year round, as we can see from the following table.
Sea temperature - Bridgetown
Sea (°F)817979818282828284828282

When to go

The best time to travel to Barbados goes from February to April, which is the least rainy of the year, but after all also December and January are acceptable, with a few more showers.

What to pack

All year round: light clothes made of cotton or linen, possibly a light sweatshirt and a light raincoat for thunderstorms; from December to March, a light sweatshirt for the evening.
For the reef, equipment for snorkeling, water shoes or rubber soled shoes.