Map from Google - Bonaire

Bonaire has a tropical climate, hot all year round, since the temperatures fluctuate throughout the year between 73 and 77 °F at night, and between 84 and 88 °F during the day. The hottest and more sultry period runs from May to October. However, the north-east trade winds blow constantly, tempering the heat.
Bonaire is a Caribbean island, about 60 miles north of the coast of Venezuela, it's an official part of the Netherlands, like the neighboring Curaçao and Aruba, and its capital is Kralendijk.
Here are the average temperatures of Kralendijk.
Average temperatures - Kralendijk
KralendijkJanFebMarAprMayJunJulAugSepOctNovDec
KralendijkJFMAMJJASOND
Min (°F)737373757577777777777573
Max (°F)848484868688888888888684

The climate is also sunny and dry, so much so that rainfall averages just 22 inches per year, with a relatively rainy period between October and December, when, however, still less than 4.3 in of rain per month fall. The rains, brought by the northeast trade winds, continue with some frequency even in January or mid-February.
Here is the average precipitation.
Average precipitation - Kralendijk
KralendijkJanFebMarAprMayJunJulAugSepOctNovDecYear
KralendijkJFMAMJJASONDY
Prec. (in)210.810.811.61.41.23.74.13.722.2
Days9533346557111172

Bonaire is a flat island, with a certain shortage of fresh water, because of the lack of rivers.

Bonaire

For swimming, the sea is warm enough throughout the year: the water temperature goes from 79 °F in February and March, to 84 °F in September and October.
Sea temperature - Bonaire
BonaireJanFebMarAprMayJunJulAugSepOctNovDec
BonaireJFMAMJJASOND
Sea (°F)817979818182828284848281

When to go

The best time to visit Bonaire runs from mid-February to May. The period from May to October is sultry, even though the trade winds make the heat bearable. From June to November, but especially from August to October, there is the danger of tropical storms and hurricanes: compared with the rest of the Caribbean, they are relatively rare at these latitudes, but they can still reach the Leeward Antilles and Bonaire. From October to December the rainfall is moderate, and sometimes the rains, though not excessive, linger on until January or mid-February.

What to pack

All year round: light tropical clothes, made of cotton or linen, possibly a light raincoat for thunderstorms, especially from October to January; those who are sensitive to cold can bring a light sweatshirt for the evening.
For the reef, equipment for snorkeling, water shoes or rubber soled shoes.