Map from Google - Kiribati

The climate of Kiribati is tropical, hot all year round, with considerable differences in rainfall, in fact the islands are scattered in the center of the Pacific Ocean, along the Equator, spanning a vast area.

- In the west, the Gilbert Islands, from which the name of the entire archipelago is derived, have an equatorial climate, rainy throughout the year, with a rainier season from December to April, and a relatively less rainy season from May to November. Even Banaba Island (or Ocean Island), separated from the others in the south-west, has a similar climate.
In the capital South Tarawa, where the daytime temperature throughout the year is around 88 °F, 75 inches of rain per year fall, with a maximum in January of 10.6 in, and a minimum in September and October of 3.5 inches per month. Heading south, the rainfall decreases gradually, until it reaches about 60 inches in the southernmost Gilbert Islands.
Here is the average precipitation in South Tarawa.
Average precipitation - South Tarawa
South TarawaJanFebMarAprMayJunJulAugSepOctNovDecYear
South TarawaJFMAMJJASONDY
Prec. (in)107.97.56.95.75.36.54.94.34.34.78.376.4
Days201920191817191918191820226

Here are the average temperatures of South Tarawa, which as you can see are very stable.
Average temperatures - South Tarawa
South TarawaJanFebMarAprMayJunJulAugSepOctNovDec
South TarawaJFMAMJJASOND
Min (°F)777777777777777777777777
Max (°F)888888888888888888888888

Even the sea is warm all year round, allowing long baths, as you can see in the following table.
Sea temperature - South Tarawa
South TarawaJanFebMarAprMayJunJulAugSepOctNovDec
South TarawaJFMAMJJASOND
Sea (°F)848282848484848484848484

- In the central area, the Phoenix Islands, almost completely uninhabited, are more arid, so that in the only inhabited atoll, Canton, just 20 in of rain per year fall, with little rain from October to February, and moderate rains in the rest of the year.

- In the east, the Line Islands, or Equatorial Sporades, almost in the middle of the Pacific Ocean, are very extended in latitude, and the rainfall amount varies depending on the area: the central islands, despite being near the Equator, are semi-arid, while the northern islands are rainy because they lie within the Intertropical Convergence Zone. So, only 18 inches per year fall in Malden Island, just south of the Equator, and precipitation exceeds 4 inches per month only in April and May; it reaches 41 inches in Christmas Island (or Kiritimati), just north of the Equator, with heavy rains practically only in March and April.
Here is the average precipitation in Christmas Island.
Average precipitation - Christmas Island
Christmas IslandJanFebMarAprMayJunJulAugSepOctNovDecYear
Christmas IslandJFMAMJJASONDY
Prec. (in)4.53.15.36.73.74.53.72.821.41.8241.3
Days161517141199899913139

The rains become much more abundant in the northern Fanning Island (or Tabuaeran), which in fact have lush vegetation, and receives 83 in of rain per year. Here, however, rainfall drops below 4 in between September and November, but even August is acceptable with 4.5 in of rain.
The southern islands (Vostok, Caroline, Flint) as regards the rainfall are halfway, receiving just more than 40 in of rain per year.
However, the temperature is high all year round even here, as we can see from the averages of Christmas Island.
Average temperatures - Christmas Island
Christmas IslandJanFebMarAprMayJunJulAugSepOctNovDec
Christmas IslandJFMAMJJASOND
Min (°F)777777777575757575757575
Max (°F)868688888888888888888888

In these eastern islands, the sea is warm all year round, even if it's just cooler than in the western ones, so that the water temperature is around 81/82 °F.

So far we have talked about the average temperature and rainfall, but it must be said that the Kiribati are strongly influenced by the phenomenon known as El Niño, as well as its opposite La Niña. With El Niño, the eastern currents which carry relatively cold water from South America, slow down, and therefore the climate becomes warmer and rainier than normal, while with La Niña the eastern currents become even more intense, so that the climate becomes cooler and drier, leading to recurrent drought, which in these atolls, flat and devoid of waterways, can cause major problems.

Being practically at the Equator, the Kiribatis are outside of the area where cyclones form, except the southern islands (Vostok, Caroline Flint), which are located at the edge of the area where they can form; in the period from November to April (although they are more likely from December to March).

Kiribati

When to go

The best time to visit the Western Kiribati (i.e. the Gilbert Islands) runs from May to November, better still, from September to November, because it is the least rainy. The Phoenix Islands, being drier, can be visited all year round, as well as the central Line Islands, while in the southern Line Islands, the period from November to April can be avoided for safety, because of the risk of cyclones.

What to pack

All year round, tropics-friendly, loose fitting clothing, sun hat, a scarf for the breeze, a light sweatshirt for the evening; light raincoat or umbrella, especially in the Gilbert Islands.