The weather in New Zealand is mostly consistent: assume it’s going to be foul and then every fine day is a bonus.
Then again, it seldom seems as bad once you are out in it.
The standard weather pattern for the South Island for much of the year is:
the arrival of a cold front with associated solid rain
p((. slowly clearing for a few days
p((. new cold front with associated solid rain
Heavy rain can occur at any time of the year but often it doesn’t last all day, showers or drizzle is the more usual weather phenomenon.
The best weather is usually associated with a large High parked out in the middle of the Tasman Sea. That can bring stable conditions for a week.
Metservice gives a useful 7 day forecast aimed at the main NZ cities but also has some specialised forecasts for mountain regions:
One of the better websites to predict weather is at the 7 day forecast page at MetVuw. The whole site is somewhat clunky, ie, looks like 2002 revisited, but the information is fantastically useful, giving rain predictions in 6 hour increments for the next, err, 7 days. If you fiddle around there are enlargements for the South Island and you can find out when the next rain is due to come through. Oh, it’s here already.
There’s also this fantastically graphic website that shows what is happening with the wind at this exact moment, ie, right now, and that can give you an idea about what the weather is doing.
Wet weather gear
Due to wet weather often being associated with wind, it’s important to take rain gear that keeps you, mostly, dry. Lightweight raincoats can make walking in the rain a whole lot more miserable, and with wind chill can lead to hypothermia, ie, a dangerous condition of losing body heat that can cause disorientation and possibly death. Take decent wet weather gear.