MetService is warning those on the West Coast of the South Island and Mt Taranaki to expect downpours.

There is a heavy rain warning to 3pm Sunday for Fiordland about and north of George Sound, and Westland about and south of Haast, with a further 50mm-70mm of rain expected. Rain will clear from the south by the afternoon.

Residents and visitors are warned that heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible.

Up the coast, a period of heavy rain is predicted to 8pm today for the ranges of Westland between Haast and Ōtira.

There is a heavy rain watch in place, too, for the headwaters of the Otago lakes and rivers to 2pm today. Rainfall may approach warning criteria.

And in the Canterbury high country, MetService was advising that northwest winds may approach severe gales in exposed places to midnight tonight.

Further north, there is a heavy rain watch in place for Taranaki, about and north of the mountain, from 2am to 2pm on Monday.

The forecast is for periods of heavy rain, and amounts may approach warning criteria.

For the rest of the country, MetService said a front will move slowly northwards onto the southern and central North Island during Monday, while an increasingly humid northerly flow affects northern New Zealand. A low originating in the subtropics should also move into the area west of the upper North Island.

On Saturday some parts of the country were warmer than the tropics, as temperatures skyrocketed above 30 degrees in many places.

MetService meteorologist Tuporo Marsters said that Hanmer Springs in Canterbury took the top spot at 34C.

Dunedin, Blenheim and Oxford also reached 31C, and heat alerts were in place for many places across the country.

Marsters said a warm northwesterly flow of air coming around from the tropics drove temperatures up.