The country has had the coolest start to summer in almost a decade.
Temperatures around the main cities on Monday were well below the median for the past decade, as a southwesterly flow welcomed summer to New Zealand.
"It's unseasonable, but it's not unusual," MetService forecaster Richard Finnie said.
Temperatures for December 1 have fluctuated for the last decade between as hot as 27C and as cold as 13C. This year was the coolest since 2006.
Auckland and Hamilton said hello to this summer with a cool 17C day, while Wellington and Christchurch recorded a chilly 14C.
In 2010, Auckland reached a balmy 25C for the first day of summer while Hamilton was even warmer, recording 27C -- 10C above its temperature this year.
The first day of summer in 2006 brought temperatures of 17C to Auckland and Hamilton and 13C to Wellington and Christchurch.
Mr Finnie said the country experienced a southwesterly flow on December 1, 2006, similar to what was moving across the country on Monday.
On the second morning of summer, those in southern parts of New Zealand had to scrape ice off windscreens as Monday's southerly faded out.
WeatherWatch head weather analyst Philip Duncan said yesterday morning was likely to have been the coldest morning for all of summer.
"This is well below average but the same high that is partially responsible for dredging up this cold air will also give us some sunny, hot days ahead," he said.
Mr Duncan said warmer westerlies would return tomorrow, bringing warm weather for the weekend and next week.
WeatherWatch said the first week of December would bring warm, windy and wet weather to southern and western parts of the country.
Two high pressure systems would remain over the country next week -- one over the top of the country and another on the bottom -- which would mean rain for some central parts of New Zealand.
High pressure would dominate the third week of December, WeatherWatch said, but a low in the western Tasman Sea would be worth keeping an eye on.
The last week of December was too far away for WeatherWatch to be certain with its forecast, but it expected increasing high pressure systems around the country, with a risk of a rain band and a southerly change.
WeatherWatch expected to release its first Christmas Day forecast next week.
Meanwhile, Niwa has forecast a high chance of El Nino developing this summer, which means more frequent westerly winds and drier conditions on the east and more rain for the west.
Niwa said between this month and February next year, lower pressures than normal were forecast over New Zealand.
Average to above average summer temperatures were expected and there was an elevated chance of an ex-tropical system coming near New Zealand, most likely between February and April.
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FIRST DAY OF SUMMER: THE LAST DECADE
City 2014 2013 2012 2011 2010 2009 2008 2007 2006 2005 2004
AKL 17C 18C 19C 21C 25C 24C 20C 21C 17C 21C 21C
HML 17C 20C 20C 20C 27C 22C 20C 22C 17C 23C 20C
WEL 14C 19C 18C 19C 16C 16C 22C 21C 13C 17C 22C
CHC 14C 20C 21C 23C 19C 14C 16C 18C 13C 16C 17C
(Temperatures by centre, rounded to nearest degree, for December 1. Source: MetService)
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MEDIAN TEMPERATURES FOR DECEMBER 1 IN THE LAST DECADE
Auckland: 21C
Hamilton: 20C
Wellington: 18C
Christchurch 17C
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HIGHS AND LOWS:
The country's warmest December 1 in the last decade was recorded in 2010, when Hamilton reached 27C.
The coldest December 1 was in 2006, when Christchurch and Wellington recorded 13C.
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THE WEATHER THIS WEEK:
Whangarei: Fine with light winds tomorrow, then cloudy periods and westerly winds Thursday and Friday. Highs around 22C and lows around 13C.
Auckland: Fine with light winds tomorrow then cloudy periods and fresh westerlies Thursday and Friday. Highs around 20C and lows around 14C.
Hamilton: Fine with westerlies developing tomorrow. Cloudy period Thursday and rain on Friday. Highs around 20C and lows around 10C.
Tauranga: Fine tomorrow and Thursday with cloud developing in the evening. Occasional rain on Friday. Highs around 21C and lows around 13C.
Wellington: Cloud developing tomorrow and northerly strengthening with evening rain on Thursday. Fine spells on Friday. Highs around 18C and lows around 11C.
Christchurch: Fine tomorrow with showers developing Thursday evening. Southwest wind and showers clearing Friday. Highs up to 24C on Thursday, lows around 9C.
Dunedin: High cloud tomorrow with chance of afternoon rain increasing on Thursday then clearing on Friday. Highs around 16C and lows around 9C.
(Source: MetService)
By Sophie Ryan of NZME. News Service
