Next three months: warmth lingers on

The La Nina climate system that helped fuel New Zealand's hottest summer in history is finally about to fizzle out - but the warmth looks set to stay. Photo / File

The La Nina climate system that stoked New Zealand's hottest recorded summer in history is finally about to fizzle out - but the warm weather looks set to linger on.

And an El Nino system could even be on the cards for the end of the year.

Niwa's climate outlook for the next three months gives a high chance of above-average temperatures right across the country.

Warm ocean waters around New Zealand, which experienced a summer marine heatwave, are forecast to persist through the next three months, but by the end of winter are expected to return to near normal west of the country.

Even though temperatures would be on the balmier side, Niwa said frosts would still happen in cooler places as we moved into the back-end of autumn.

Rainfall levels were also predicted to be above normal in the north and east of the North Island, while the west of the South Island would likely receive near-normal falls, and everywhere else would see near-normal or above-normal rain.

Soil-moisture levels and river flows would be above normal in the north and east of the North Island and in the north of the South Island, near normal or above normal, in the west of the North Island, and near normal in the west and east of the South Island.

In the background, La Nina conditions have carried on through this month but trends in winds and sea-surface temperatures indicated its influence was coming to an end.

"Even though La Nina's influence will wane over the next three-month period, New Zealand's regional climate over April to June 2018 is expected to be driven by persistence of more northeasterly airflow than normal, and by the persistence of warm ocean waters that are present around the country," Niwa reported.

"The northern Tasman Sea will remain unsettled, with lower pressures than normal, bringing the likelihood of significant rainfall events to the North Island and the upper South Island."

International models suggested the tropical Pacific would also move into an ENSO-neutral state over the next three months.

But perhaps not for long - toward the end of the year there was currently an equal chance of it staying that way or shifting toward an El Nino system over spring.

In New Zealand, El Nino systems typically brings cooler, wetter conditions, bringing higher rainfall to regions that are normally wet, and often drought to areas that are usually dry.

Farmers in the western, wetter parts of the country often faced significant damage to pastures from too much rainfall, and it was also harder for stock to thrive in the constant wet.