The climate in Sint Maarten is tropical, hot and sunny all year round: the daily average temperature ranges from 25 degrees Celsius (77 °F) between January and March to 28 °C (82 °F) between June and October. The night temperature rarely drops below 20 °C (68 °F), while sometimes it can reach 35/37 °C (95/99 °F) during the day, from June to November. In the warmest season, there's hot and muggy weather, though the breeze gives some relief.
Here are the average temperatures of Philipsburg, the capital.
Philipsburg - Average temperatures
Min (°C)222223232425252526252423
Max (°C)282728282930303131302928
Min (°F)727273737577777779777573
Max (°F)828182828486868888868482

Sint Maarten is an island of the Lesser Antilles, located at a latitude of 18 ° north, and it's administratively divided between France and the Netherlands; here we are dealing with the Dutch side, located in the south (on the French side we find instead Saint Martin).
Normally the rainfall is not abundant, since the annual average amounts to around 1,000 millimeters (40 inches); February and March are the least rainy months, with about 45/50 mm (1.8/2 in) per month, while the rainiest period runs from August to November.
Here is the average precipitation.
Philipsburg - Average precipitation

However, the rains occur in the form of downpours or thunderstorms, which do not last long, so much so that the sun shines throughout the year, as can be seen in the following table.
Philipsburg - Sunshine


In Sint Maarten, the sea is warm enough for swimming all year round, even though it is a bit warmer in the summer months, as we can see from the following table.
Sint Maarten - Sea temperature
Temp (°C)262626262728282829292827
Temp (°F)797979798182828284848281


In the period from June to November (but mostly from August to October), Sint Maarten can be hit by tropical depressions and hurricanes, as happens in general in the Caribbean.

Best Time

The best time to visit the island where Sint Maarten is located goes from December to April, since it's the least hot and outside the hurricane season; in particular, the period from February to March is usually the least rainy. In May, both temperature and moisture increase, but the rains are not yet too abundant, and we are still out of the hurricane season. In summer, June and July are not as rainy as August and September, in addition, tropical storms and hurricanes are less likely to occur than in the following months.

What to pack

All year round: bring light clothes of natural fabric, and possibly a light sweatshirt and a light raincoat for thunderstorms, especially from August to November. A light sweatshirt for the evening from December to March.
When going to the reef, you can bring snorkeling equipment, including water shoes or rubber-soled shoes.