Map from Google - Curaçao

In Curaçao the climate is tropical, hot all year round, with daytime temperatures ranging from around 28/29 degrees Celsius (82/84 °F) in December, January and February, to around 31 °C (88 °F) from May to October. The period from May to October is the most sultry, but the trade winds blow constantly, tempering the heat.
Curaçao is an island, and like the neighbouring islands of Bonaire and Aruba, it's part of the Kingdom of the Netherlands.
Here are the average temperatures of the capital Willemstad.
Average temperatures - Willemstad
WillemstadJanFebMarAprMayJunJulAugSepOctNovDec
WillemstadJFMAMJJASOND
Min (°C)242425252626262626262625
Max (°C)282930303131313131313029
Min (°F)757577777979797979797977
Max (°F)828486868888888888888684

The climate is sunny and dry, so that about 550 millimetres (21.6 inches) of rain per year fall. The only relatively rainy period goes from October to December, in which, however, precipitation does not go beyond 80/100 mm (3.1/4 in) per month. From November to January or mid-February, the northeast trade winds bring showers quite frequently, although usually not abundant.
Here is the average precipitation.
Average precipitation - Willemstad
WillemstadJanFebMarAprMayJunJulAugSepOctNovDecYear
WillemstadJFMAMJJASONDY
Prec. (mm)4525142020194042498497100555
Prec.(in)1.810.60.80.80.71.61.71.93.33.83.921.9
Days9533236557101270

Curaçao is an almost entirely flat island: its highest point is located at 375 metres (1,200 feet) above sea level.
The sunshine amount is good all year round, as can be seen in the following table.
Sunshine - Willemstad
WillemstadJanFebMarAprMayJunJulAugSepOctNovDec
WillemstadJFMAMJJASOND
Sun (hours)899889999888

From June to November, but especially from August to October, there is the danger of tropical storms and hurricanes, which, however, are rare in Curaçao and the Leeward Antilles, because of their southern location. A hurricane that hit Curaçao along with Aruba and Bonaire was Joan, which passed in October 1988, bringing strong winds and abundant rainfall, and causing widespread flooding.

Curaçao

For swimming and sun bathing, the sea is warm enough throughout the year: the water temperature goes from 26 °C (79 °F) in February and March, to 29 °C (84 °F) in September and October.
Sea temperature - Curaçao
CuraçaoJanFebMarAprMayJunJulAugSepOctNovDec
CuraçaoJFMAMJJASOND
Sea (°C)272626272728282829292827
Sea (°F)817979818182828284848281

When to go

The best time to visit Curaçao runs from mid-February to May. The period from October to December (and sometimes even January and the first half of February) is quite rainy.

What to pack

All year round: light, loose fitting clothes, 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.