Well, as they say, there's no inappropriate weather - only inappropriate gear. I'm not so sure if my fishing outfit is appropriate but it keeps me toasty (and to Grant's relief, keeps me from moaning about being cold and wanting to go ashore!)
Biggles, your friends will be arriving in the height of winter - and, yes, they are going to freeze. Chris is right though - the temps will vary dramatically depending on location. And in some places, like Christchurch, you can actually experience all four seasons in one day!
jky - your photos are fantastic! Definitely looks like a 100 mile trip and fifty degree water are worth the effort - wow. really amazing stuff.
Holy Schmokes, Pathalla - I just found your thread on the War Machine! Now, that's a RIB!!