There is no sugar-coating it, the weather over the next three months looks like it could be a bag of liquid allsorts.
Niwa principal forecaster Chris Brandolino said changing airflows meant changing weather from now until March.
"La Nina hasn't gone away ... the weather is going to be mixed."
He said there was an increased likelihood of more westerly winds than previously indicated, but this pattern was expected to be interspersed with easterly air flows, especially during periods of La Nina-like weather.
"There is enhanced potential for rain events linked to the tropics and sub-tropics to impact the country from mid-January through to March.
"Apart from the west and east of the South Island, the rest of New Zealand has about equal chances for near normal or above normal rainfall for the coming three months.
"Areas not exposed to rain-bearing weather systems may experience extended dry spells, such as in the first half of January."
Mr Brandolino said the change in air flow patterns also increased the odds of cooler than usual summertime temperatures.
On the West Coast, the Southern Alps and foothills, Otago and Southland, temperatures were about equally likely to be near average or above average, and rainfall totals were most likely to be near normal, he said.
"After a period of unusually dry weather through about mid-January, the pattern is expected to favour increased periods of unsettled conditions everywhere except coastal Otago."
As a result, soil moisture levels and river flows were equally likely to be near normal or below normal, he said.
Coastal sea surface temperatures (SSTs) ranged from about 0.8C to 1.6C above average around the country by the end of December, but marine heatwave conditions have receded recently.
Mr Brandolino said global climate forecasts were for SSTs to remain above average around New Zealand during the rest of summer.
"While marine heatwaves [MHW] remain possible over the coming three months, given the aforementioned change in air flow patterns and the expected absence of persistent high pressure, widespread MHW conditions are less likely than previously believed."
A La Nina watch remained in effect, he said.
