The climate of Nauru, a small island of the Pacific Ocean located at the Equator, is equatorial, hot and humid throughout the year, with constant rains and no dry season. We can still distinguish a rainier period from December to April, when more than 150 millimeters (6 inches) fall per month, with a maximum 250 mm (10 in) or more per month from December to February, and a drier period from May to November, when, however, still from 100 to 150 mm (4 to 6 in) of rain fall per month.
Precipitation amounts to around 2,000 mm (80 in) per year. Rainfall can vary from year to year; in fact, it can sometimes rain a lot even in the least rainy season. However, June is the month that historically has had the lowest rainfall records. The rains occur in the form of showers or thunderstorms, which may be intense, but do not last long, so the sun has always a chance to shine.
Here is the average precipitation.
Nauru - Average precipitation

The average temperature is extremely stable during the year: lows hover around 24/25 °C (75/77 °F) and highs around 30 °C (86 °F). There is just a slight rise in temperatures between October and December. Sometimes, however, the temperature can reach 35 °C (95 °F) from November to April.
Here are the average temperatures.
Nauru - Average temperatures
Min (°C)242424242525242424252524
Max (°C)303030303030303030313130
Min (°F)757575757777757575777775
Max (°F)868686868686868686888886

Since at the Equator there is no Coriolis effect, which is necessary to give life to cyclonic vortices, Nauru is outside of the path of tropical cyclones.

Nauru, from above

The sea in Nauru is pleasantly warm all year round, and has a very stable temperature too, as can be seen in the following table.
Nauru - Sea temperature
Temp (°C)292929292929292929292929
Temp (°F)848484848484848484848484

Best Time

Since it is not affected by tropical cyclones, in theory, you can go to Nauru throughout the year, however, the period from December to February is very rainy. So, the best time to visit Nauru runs from May to November, since it is the least rainy period of the year, though showers and thunderstorms may occur even in this period. The period from May to August is even better because it is slightly less sultry.
The natural environment of Nauru is still suffering because of the intense mining of phosphates made in the past, and the island is not well equipped for tourism. However, the sea lends itself to swimming and diving, and as previously mentioned, it is pleasantly warm all year round.

What to pack

All year round, bring tropics-friendly, loose-fitting clothing, a sun hat, a scarf for the breeze, a light sweatshirt for the evening, and a light raincoat or umbrella.