Summery week for Whanganui in sizzling La Niña summer

Whanganui beaches are likely to be packed, during another week of summer weather. Photo / Lewis Gardner

Whanganui is in for an extra hot three months with spots of "binge rainfall", according to Niwa.

And MetService isn't expecting rain in the Whanganui area until January 19, with a very dry two weeks ahead.

Niwa principal scientist Chris Brandolino said the La Niña weather pattern was expected to influence the local climate for at least the next three months.

It was likely to have warmer weather, for long periods, but there may also be some heavy dumps of ex-tropical cyclone rain, he said.

La Niña is a weather pattern from the equatorial Pacific.

It typically brings more northeast winds from the warm seas of the equator, and for Whanganui the northeast is a warm wind.

"It comes off the central plateau and keeps the cooler air from the sea off the coast.

"Your weather generally comes from the west. This is going in the opposite direction," Brandolino said.

Another factor making this summer hotter is a record-breaking marine heatwave around New Zealand, Niwa said in a climate outlook to March 2022.

It has continued since late November and the water off the Whanganui coast is 2 to 2.5C warmer than usual.

"That has a lot to do with our air temperatures," Brandolino said.

"It loads the dice. It makes it challenging to get any prolonged chillier temperature."

Adding to that is climate change in the background, accentuating both extreme warmth and dryness and extreme rainfall, Brandolino said.

This summer could be similar to 2017-18, according to the climate outlook.

January 2018 was the warmest month of any on record for New Zealand.

Whanganui was likely to have nights of 16-17C, and water vapour in the air will make them humid as well.

Rainfall was likely to be "lumpy", Brandolino said.

Overall the amount may be average or below average, but there could be a lot of extended dry spells of days or weeks. Drought is a distinct possibility.

"It's binge rainfall, when the heavens open up," Brandolino said.

"You could get a month's or two months' rain in a day or two, with meanwhile dry weather all around the event."

The pattern could be similar to the big dumps of rain Whanganui got in December, he said.

That rain caused some flooding, but also set farmers up for one of the best late springs Taihape resident Fraser Gordon has farmed in.

"It was the best lambing I have ever had. It's hard to complain at the moment," he said.

More such rain in the next two weeks would set him up until mid-February, he said.

MetService meteorologist Dan Corrigan said daily temperatures over the next few days would be around 25C.

Monday morning was the only day with a threat of rain until January 19, he said.

"It's looking like a very settled, summery week in Whanganui, going into the second full week of 2022.

"It's a good week to spend some time outdoors."

Winds have been west and northwest in Whanganui.

Temperatures were set to dip to highs of 24C on Wednesday, Thursday and Friday, when the wind changes to south east.