Despite a harshly quick descent into winter weather that many around the country would have uncomfortably noticed, temperatures across the cold season aren't predicted to be too bitter.

The National Institute of Water and Atmosphere (Niwa) issued its climate outlook today, projecting that temperatures were "very likely", with a probability of between 65 per cent and 80 per cent, to be above average in all regions.

This follows a run of unusually warm months -- February 2016 was the hottest on the books -- that meteorologists put down to a high number of northerlies, an absence of southerlies and unusually warm seas around the entire country.

Nevertheless, Niwa said, frosts would still occur from time to time in cooler places this winter.

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And not all of New Zealand would get treated to the buffet of sunny, warm days that had been unusually dished up by autumn this year.

Rainfall levels, too, were likely to be above normal (a 50 per cent chance) in the north and west of the North Island and the west of the South Island, and either near or above normal in the east of the North Island and the north and east of the South Island.

Soil moisture levels and river flows, meanwhile, were likely to be in the above-normal range in the north and west of the North Island and the west of the South Island, and most likely to be in the near-normal range in the east of the North Island.

A cold southerly covers the country but a big high pressure system is coming for the weekend and next week. While a few coastal showers will continue most places will be settled, with a warm subtropical flow coming in next week.

In the north of the South Island, soil moisture and river flows would either be, near or above normal and in the east of the South Island, levels would be near or below normal.

Sea surface temperatures were forecast to be above normal over the next three months, especially to the west of New Zealand.

The predictions came as ocean-atmosphere conditions in the tropical Pacific had now returned to near normal after a rapid demise of El Nino, which peaked late last year.

"Sea surface temperatures in the central Pacific are close to average, and slightly cooler than normal ocean temperatures have emerged along the equator in the eastern Pacific," Niwa reported.

Atmospheric circulation along the equatorial Pacific had returned to near-normal, and the Southern Oscillation Index -- a pressure-measuring climate tool used as an indicator of the development and intensity of El Nino or La Nina events in the ocean -- had also returned to near-neutral values.

Cooler than normal sub-surface ocean waters had continued to intensify and spread eastward along the equatorial Pacific, suggesting the possibility of La Nina conditions developing this year.