While December kicked off with stormy weather, the rest of the month is expected to fluctuate between settled and unsettled bouts. Temperatures will likely be warmer in the North and cooler in the South.
The wet start to December followed by an upcoming settled spell is the sort of variability the rest of the month could see.
According to NIWA's Seasonal Climate Outlook for December 2018 to February 2019, this month will most likely see bouts of settled and unsettled weather between weeks.
While mid-December looks settled, the outlook for later in the month especially around 24, 25 and 26 could be unsettled, meaning there could be a rain storm either side of those dates.
The second week is expected to be dry, the third week will welcome showers.
Compare New Zealand's soil moisture deficit in Dec 2017 () to Dec 2018 (️).— NIWA Weather (@NiwaWeather) December 5, 2018
A striking year-over-year difference! pic.twitter.com/LJ1sJyZ2ET
NIWA Meteorologist Ben Noll said the week leading up to Christmas, starting on Monday 17 December, looked like it would begin to turn unsettled to the west of New Zealand, over the Tasman Sea.
"This could mean that a few fronts move across the country, bringing some rainfall and cloudiness. Some of the moisture could streak down from the tropics and be heavy.
"A northwesterly or westerly wind flow is also most likely, which could mean that the highest chances for dry weather will be found on the east coast of both islands, particularly the North Island."
Temperatures will most likely be on the warmer side in the North Island, and a bit cooler in the South Island.
"Of course, Christmas Day could deviate from the general pattern described above - even in a busy weather pattern there can be a day or two that has more tranquil conditions," Mr Noll said.
"It is possible that more settled weather arrives during the period between Christmas and the New Year, but we'll still need to keep an eye on the tropics to the north of New Zealand."
Spring 2018 is officially in the books!— NIWA Weather (@NiwaWeather) December 5, 2018
↔️ The first season since summer 2016-17 that no main centres had above avg temps.
️ Oamaru had 326 mm of rain, 3x spring normal & 69% of the annual normal.
Driest spring on record for the North Shore & Western Springs (Auckland). pic.twitter.com/ZiFX79mdZE
Over the next three months, near normal summer rainfall is to be expected for most regions.
However, the north of the North Island has about equal chances for below normal or near normal rainfall and the west of the South Island has about equal chances for above normal or near normal rainfall.
Sea surface temperatures in coastal waters during the next three months are placed to be above or near average. In late November they were reported to be above average.
The month of January, however, could be the month of the summer with favourable weather.