Its hard to say what the weather will be like. The thing with Fiji is if you are experiencing bad weather, drive somewhere for an hour or two and you will have sunshine. You can have storms on the islands and head into Viti and find perfect weather,, visa versa as well.
If you want to come to fiji then come.
We go every 10 weeks or so for a week, you can never pick it.. November 08 was the best weather I have seen, perfect nights with sunny warm days. Every other time it has been beautiful in the morning, overcast or storming in the afternoon. Some times it can be overcast for days with drizzle but stinking heat.
The great thing about Fiji is if you experience off weather,, it gives you the opportunity to get out an about and experience other things other than swimming and snorkling.
Enjoy :-)