Sticky, humid weather awaits the country this summer as a weak La Nina brings muggy weather particularly in northern areas.

That'll be unwelcome news for those in the upper North Island, who suffered through levels of 90 to 100 per cent humidity on Friday.

"With humidity levels so high coupled with higher temperatures many people were complaining to us and on social media yesterday about the 'muggy' conditions," said WeatherWatch head analyst Philip Duncan.

At the peak of the complaints Auckland, Hamilton, Tauranga and Whangarei were all hovering around 96 to 99 per cent humidity with temperatures around the low 20C mark.


Thanks to a high north of the country fuelling a sub-tropical air flow down over the upper North Island, Friday saw humidity levels rise with ongoing downpours, fog and an increase in cloud.

"Global scientists have already declared a weak La Nina is here - and for New Zealand, especially northerners, this usually means more days like yesterday," Duncan said.

"So, that means this summer is expected to be wetter, cloudier and more humid than average."

Combined with summer heat and many muggy days can be expected over the coming months.

This morning humidity levels were fairly high again in the north responsible for fog patches across Waikato, Auckland and Northland.

Over the next couple of days the humidity will continue to drop, with windy westerlies bringing temperatures down tomorrow and into Monday.

Meanwhile heavy rain is forecast for the west of the South Island, Canterbury and Otago.

MetService sent out a severe weather warning this morning, advising people in these areas are advised to look out for rapidly rising streams and rivers, slips and surface flooding today and into tomorrow.

The heaviest falls are likely about Westland and northern Fiordland, with significant spillover into the headwaters of the Canterbury and Otago lakes and rivers.

About the ranges of Westland, another 80 to 120mm of rain may accumulate through into early Sunday morning, while 50 to 70mm is possible in Fiordland north of Doubtful Sound until this evening on top of what has already fallen.

For the Canterbury and Otago headwaters, another 50 to 80mm is possible within 10km east of the main divide, MetService said.

In addition, periods of west to northwest gales are also likely across much of central and southern New Zealand over the next few days.

The strongest winds are expected about Clutha and Southland until around midday today, where gusts of 120km/h or more are likely.

Winds of this strength could damage trees and powerlines, and make driving hazardous.