6:27 p.m. on January 25, 2005 (EST)
I haven't been to the Fjordlands, but just north of them (Milford Sound, Mt Cook area, kayaking along the coast). Depending on when you are going, you can be fairly lucky as far as weather is concerned, but in general it will rain at some point every day. Some of the rain will be heavy and wind driven.
If you are staying on one of the Trecks, or marked hiking trails, you usually have the option of staying at a hut every couple of days, or maybe even every day, which gives you some chance to dry out.
A lot of Kiwi guides spin the "GoreTex won't work, you need a heavy 1950s rain slicker." Except for some older guys who wore rain slickers because they had for decades, I haven't met anyone who was happy with that stuff. Too heavy and sweaty. I have heard no credible story of GoreTex or similar high quality fabrics failing in NZ rain. But some do wet out on the outside cutting breathability. So the things I would look for are:
-quality rainwear that's proven to work on hour long rain
-good to excellent DWR (durable water repellant). If you can, wear the garment in the shower for ten minutes and if the water stops breading off, return it. (Put the tags in the pockets or Ziplock bags.)
-tight zippers
-good venting options and good breathability (Gore XCR, Packlite, eVent,....) if it rains in NZ, you can bet on 100% humidity.
I don't know if I would take some of the $99 rainwear like the Precip or REI Elements. I hear rumors that they don't do too well after a few hours and they are simply not very comfortable to wear for long stretches of time.
Oh, and if you are not climbing, don't get something overbuilt.
Mountain Hardwear is a good brand, but I'd stay away from their Conduit Silk shells. They are light and cheap, but IMO not that suitable for anything more than moderate rain. Other options include Marmot (leave the most basic Precip), Patagonia (H2NO is a bit less breatable than the other stuff, but their quality and DWR is great), LLBean (GoreTex only) on the lower end, and Arcteryx on the high end.
A lot of places currently have Arcteryx Theta SL jackets on sale for about $250. If you want to spend that much, and find one that fits you, I think it might be almost perfect for your trip (and the next 5 years).
http://froogle.google.com/froogle?q=theta+sl&btnG=Search+Froogle