"It's mother nature's way of saying 'get out of the city and go on holiday'."
Duncan said the calmest, driest weather would be in the north and east. But holidaymakers should still pack a woolly jumper as temperatures would drop. The South Island can expect to be around 11C to 17C while the North Island will be a bit warmer in the low 20Cs.
Don't get used to the dry conditions too soon either.
Duncan warned the weather was set to go downhill again on Sunday.
New Zealand is stuck in a late spring pattern which is bringing changeable weather to the country.
"We have to get used to the cloud, it's going to be with us until the second week of January.
"Every year we get asked 'Why isn't the weather perfect?'. But we're two islands in the roaring 40s.
"It's called Aotearoa for a reason with the amount of cloud we get."
Duncan said Southland would get the coldest weather, while Hawkes Bay and East Cape would get the hottest. The wettest place would be the west coast of the South Island and the cloudiest would be the north-west.
Duncan said Kiwis shouldn't lose hope for a good strong summer. He thought there could be a "dramatic change" in late January or early February. A heatwave from Australia or a wet tropical event from the Pacific could find its way to New Zealand.
Despite the late start to summer the warm balmy weather could carry on late into 2017, Duncan said.
"It's not all doom and gloom."
This week's temperatures:
Whangarei
Dec 29: Cloudy with light rain and westerlies. High 23C, low 14C
Dec 30: Cloudy periods, chance of an afternoon shower. Light winds. High 22C, low 13C
New Year's Eve: Fine spells, chance of an afternoon shower. Light winds. High 24C, low 15C
New Year's Day: Mainly fine with light winds. High 26C, low 15C
Auckland
Dec 29: Cloudy periods with light rain. Southwesterly winds. High 19C, low 12C
Dec 30: Cloudy periods, chance of an afternoon shower. Light winds. High 22C, low 13C
New Year's Eve: Fine spells, chance of an afternoon shower. Light winds. High 23C, low 15C
New Year's Day: Cloudy periods, chance of a shower. Westerly develops. High 23C, low 17C
Tauranga
Dec 29: Cloudy periods. Chance of a shower. Westerlies. High 22C, low 11C
Dec 30: Fine spells, chance of an afternoon shower. Light winds. High 22C, low 13C
New Year's Eve: Fine spells, chance of an afternoon shower. Light winds. High 23C, low 15C
New Year's Day: Cloudy periods, chance of a shower. Westerly develops. High 23C, low 17C
Rotorua
Dec 29: Cloudy periods. Chance of a shower. Westerlies. High 20C, low 8C
Dec 30: Fine. Light winds, afternoon northerlies. High 22C, low 9C
New Year's Eve: Fine. Light winds, afternoon northerlies. High 23C, low 12C
New Year's Day: Cloudy periods increasing. Westerlies developing. High 23C, low 15C
Napier
Dec 29: Fine at first. Light rain from the afternoon. Southerlies. High 22C, low 10C
Dec 30: Fine in the morning. Southerlies dying out. High 20C, low 10C
New Year's Eve: Fine. Northerlies developing. High 23C, low 15C
New Year's Day: High cloud increasing. Northwesterlies strengthening. High 29C, low 19C
Wellington
Dec 29: Occasional light rain. Clears in the evening. Freshening southerly. High 15C, low 10C
Dec 30: Fine. Northerlies developing. High 19C, low 12C
New Year's Eve: Mainly fine with northerlies strengthening. High 18C, low 15C
New Year's Day: Cloudy, with a few spots of rain. Strong northwesterlies. High 19C, low 15C
Christchurch
Dec 29: Occasional drizzle, clearing in the afternoon. Light winds. High 15C, low 7C
Dec 30: Fine with northeasterlies developing. High 20C, low 9C
New Year's Eve: High cloud. Northeasterlies freshening. High 24C, low 15C
New Year's Day: High cloud. Winds turning northwest. High 30C, low 13C
Dunedin
Dec 29: Few showers, clearing evening. Southwest eases. High 14C, low 9C
Dec 30: Fine spells with light winds. High 17C, low 11C
New Year's Eve: High cloud, chance of late rain. Northeasterlies. High 20C, low 14C
New Year's Day: Few showers, mainly morning. Southwest change. High 21C, low 13C
