Just got back from Fiji 1 weeks ago it it was the start of the rain (wet) season. We didn't encounter any rain at all the whole time we were there and we were on Denanru Island which is just off the main island. Another couple we met however we ataying in Suva for most of their trip and had rain the whole time. Out on Mana and other islands it was sunny the whole time so i guess it just depends on where you are planning on staying.
It was really overcast in the afternoon but the mornings were fantastic. It was the best time to be out on the water for water sports. almost 8 years ago