Majority of South Island under weather warnings and watches with flooding, slips possible

The vast majority of the South Island, and part of the lower North Island, are under weather warnings and watches for heavy rain and strong winds.

Flooding and slips were possible - and rivers and streams could rise rapidly.

MetService said a front, preceded by a strong northwest flow, was moving over the south of the South Island on Friday, heading north over the weekend.

Parts of the South Island covered by an orange heavy rain warning include:

Coastal ranges of the districts of Buller and Grey from 11am Saturday until 2am Sunday

The ranges of Westland from 7pm Friday until 7pm Saturday

Headwaters of the Canterbury lakes and rivers south of the Hurunui River from midnight Friday until 7pm Saturday

Headwaters of the Otago lakes and rivers from 10pm Friday until 2pm Saturday

Fiordland from 7pm Friday until 1pm Saturday

Areas covered by an orange strong wind warning are:

Canterbury High Country from 3am until 3pm Saturday

Heavy rain watches are in place for:

The Tararua Range from 11pm Saturday until 8am Sunday

Inland ranges of the Buller District and the Nelson Lakes from 11am Saturday until 2am Sunday

Strong wind watches are in place for:

Wellington and Wairarapa, south of Carterton, from 12pm Saturday until 5am Sunday

Southland, inland Otago and western Clutha from 9pm Friday until 10am Saturday

Marlborough Sounds and inland ranges of Marlborough from 9am Saturday until 2am Sunday

MetService said on Friday, northwesterly winds would begin over the South Island before the rain came.

"Powerful winds are on the cards for some eastern regions for much of the weekend, strengthening about Wellington and the Wairarapa by Saturday.

"Heavy rain is expected for western areas of the South Island on Saturday, and along the spine of the Southern Alps, with thunderstorms possible.

"Heavy rain could spill into the headwaters of the Canterbury and Otago lakes and rivers, causing them to rise rapidly."

MetService said people heading to the Super Rugby final on Saturday in Wellington should wear a rain jacket rather than take an umbrella as showers are expected to turn to rain in the evening - with strong northwesterlies accompanying it.

"By the Winter Solstice on Sunday, this band of rain pushes over the North Island," MetService said.

"Heavier falls are forecast about the Tararua ranges and central parts of the North Island."

Warm temperatures can be expected over the weekend with Christchurch expected to reach 21C on Saturday, MetService said, but it won't last - with a risk of "turbulent weather" on the way.

"Frosty winter conditions return to the South Island on Monday, with a brief period of settled weather."