This summer looks set to be wetter and windier than usual for some parts of New Zealand.
A change in air flow patterns means there will be mixed weather through to March.
In Niwa's seasonal climate outlook from January through to March, a La Niña watch will also remain in place.
La Niña refers to a cooling of the tropical Pacific Ocean and the subsequent shift in global weather patterns, including a strengthening of moist easterly winds blowing towards New Zealand, and a subsequent increase in cloud development and rain over the longitudes.
It is only the second time in 75 years that a La Niña onset has arrived in summer.
It usually forms in winter, peaks in late spring, and then gradually weakens through summer.
La Niña will bring moist, rainy conditions to northeastern areas of the North Island and reduced rainfall to the lower and western South Island.
Niwa said there was also an enhanced potential for rain events linked to the tropics and sub-tropics to affect the country from mid-January through to March.
Apart from the west and east of the South Island, which may experience extended dry spells, the rest of the country has a chance of above-normal rainfall for the next three months.
Warmer-than-average air and sea temperatures were also likely for the North Island, with about equal chances for near-average or above-average seasonal temperatures for the South Island.
The change in air flow patterns will also increase the odds for spells of cooler-than-usual summertime temperatures.
