We have been in the Taveuni and surrounding area in the month of April. We stayed at Matangi island in the Taveuni area.
The water temps I suspect in September should be around 75-79 degrees F as it is coming to the end of their winter. I dove in surf shorts and nylon shirt but I don't mind it. My wife on the other hand wore a 3mm and is always cold even in 85 degree water. I did bring my 3mm but didn't use it except for a few dives.
We found the currents could be strong and with quite a bit of surge especially around the SomoSomo straights sites (Great White wall, etc) and some around Qamea. We found less current around Yellow and Noels walls but this is more of a trip from Taveuni. Great diving there though. The currents and surge at some sites meant quite a bit of finning at times.
Do bring an UW camera if you have one. The soft corals are fantastic and the colors will vary significantly along with giant clams, anemones and fish, a few sharks, eels (blue ribbon and spotted morays, octopus and tons of small fish.
The island hopper airlines do say they have weight limits on baggage which is far less than the international flights and that there is a charge for overweight bags however we were not charged on any flight. It may be due to how full the flight is, what mood the desk agent is in, etc. Be prepared to pay though. We brought all our own dive gear.
The electricity is 240V and 50 hz. I had a transformer (not plug adapter) that did not work (I suspect I got what I paid for) so if you have batteries to charge or other personal appliances that run 110V 60hz, contact the resort to see if they have a charging station or provide appliances for 240V.
Do see the Tavoro waterfalls in Bouma National park. Everyone there refers to them as Bouma Falls. There are 3 waterfalls at ascending elevations and the first is a very easy walk from the park entrance. The other two are more of a hike so bring appropriate shoes for those. It can get slippery i.e. lots of rain. I think it's about $8 FJ to get in. I recall that Sundays are the kid’s free day so the lower falls can be a bit busy but when we were there the kids left after a bit and my wife and I were the only ones there for quite some time. Also the kids can show you where to jump off the small cliff to avoid the big rock. The cliff rocks are very slippery and it's better to go up them barefoot (or bring appropriate beach shoes). The water is a bit chilly though. My SB avatar is the lower falls.
We did bring school supplies - pencils and paper. It is appreciated.
For some reason, hot tea is sometimes provided on SI's. I am not a tea drinker and hot beverages on a hot day don’t do much for me so we started bringing our own bottled water on dives.
The recommendation for dress was to cover up in public (apart from the resort) with light pants or sarong for women. Also shoes off when going indoors.
Taveuni and area can get rain so I would bring hats and possibly a light raincoat.
If you need souvenirs, you can get some in Taveuni especially carvings. If you have time in Nadi, Jacks has everything including pearls (Tahitian when we were there but they are developing their own industry). Some of it is pricey but generally good quality all around.
If you are looking for night life there isn't alot (or none).
We did take some bug spray for mosquitos around dusk but they were not bad. Again, we were there in April.
It took awhile to get there so relax and go with the flow. We did have flight delays (5 hours in Nadi to Taveuni) and unscheduled stops (from itinerary).
We overpacked, so next time, less of many things.
