Map from Google - Micronesia

In the Federated States of Micronesia, the climate is equatorial, ie hot, humid and rainy throughout the year.
The temperature is definitely stable throughout the year, around 22/25 °C (72/77 °F) at night, and 30/32 °C (86/90 °F) during the day; it rarely drops below 20 °C (68 °F), while sometimes it can reach 34/35 °C (93/95 °F).
Here are the average temperatures of the capital Palikir.
Average temperatures - Palikir
PalikirJanFebMarAprMayJunJulAugSepOctNovDec
PalikirJFMAMJJASOND
Min (°C)232423232322222222222223
Max (°C)303030303030313131313130
Min (°F)737573737372727272727273
Max (°F)868686868686888888888886

The islands are located just north of the Equator, and are affected by the trade winds, constant winds which are able to temper a bit the heat.
The amount of sunshine is never excellent, given the frequent rains, but neither it is too low, as the rains occur in the form of short and intense showers and thunderstorms.
The annual precipitation is abundant, and ranges from 2,500 to 5,000 millimetres (100 to 200 inches), but in the windward slopes of the larger islands (such as Pohnpei and Kosrae), in which there are some elevations in the interior, it can exceed 6,000 mm (235 in) per year, that is, six metres (20 feet)! Mount Nahnalaud, 750 metres (2,450 ft) high, on the island of Pohnpei, is one of the wettest places on Earth, with 10,160 mm (400 in) of rain per year, and it is often covered with clouds.
The capital Palikir, in the island of Pohnpei (ex Ponape), receives almost 4,800 mm (190 in) of rain per year, with a minimum of 260 mm (10.2 in) in February, and a maximum of 490 mm (19.3 in) in May. Here is the average precipitation.
Average precipitation - Palikir
PalikirJanFebMarAprMayJunJulAugSepOctNovDecYear
PalikirJFMAMJJASONDY
Prec. (mm)3002603604404904304404204004104004004750
Prec.(in)11.810.214.217.319.316.917.316.515.716.115.715.7187
Days211920202019222220212021245

The driest islands are the flat atolls, where there are no hills and mountains which could enhance the formation of thunderclouds: in these cases, precipitation can drop below 4,000 mm (157 in) per year, and in some cases even below 3,000 mm (118 in).
However, the rainfall pattern is quite irregular from year to year, because the country is affected by the so-called ENSO cycle: in particular, the phenomenon known as El Niño can cause drought in this area of the Pacific.

In the westernmost island, Yap, 3,000 mm (118 in) of rain per year fall; the period from February to April is (relatively) less rainy, since rainfall does not exceed 160 mm (6.3 in) per month, which, however, is still a considerable amount.
In Chuuk, rainfall totals 3,500 mm (138 in) per year, with a minimum of 170 mm (6.7 in) in February, and a maximum of 360 mm (14 in) in May. From January to March, precipitation drops below 250 mm (10 in) per month.
In the southern island of Nukuoro, rainfall amounts to 4,000 mm (157 in) per year, though the pattern is different, because it drops below 300 mm (12 in) per month from September to December; in the even more southern Kapingamarangi, rainfall amounts to 3,000 mm (118 in), and it drops below 250 mm (10 in) from August to December, and below 200 mm (8 in) in September and October.

Micronesia may be affected by tropical cyclones of the North Pacific Ocean, known in this area as typhoons, which occur in the period from June to November. Sometimes typhoons have developed outside of this period, as has been the case with Pamela (May 1976), Isa (April 1997), Mitag (February-March 2002) and Sudal (April 2004). An exception is represented the southern atoll of Kapingamarangi, which is sheltered from typhoons, because it's located practically at the Equator (therefore it can be visited all year round).

Pohnpei

The sea in Micronesia is pleasantly warm all year round, and has a very stable temperature, as we can see in the following table.
Sea temperature - Palikir
PalikirJanFebMarAprMayJunJulAugSepOctNovDec
PalikirJFMAMJJASOND
Sea (°C)292929292929292929292929
Sea (°F)848484848484848484848484

When to go

The best time to visit Micronesia is from February to April in the westernmost islands (Yap Islands), and from January to March in the central-eastern islands (Caroline Islands), being the driest (or rather the least rainy). Typically February is the "driest" month of all. However, considering the risk of typhoons, which as mentioned have occurred, though rarely, from late February onwards, for safety you can choose the period from mid-December to mid-February.

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.