Summer solstice: Longest day of the year today

The official start of summer: today has the most sunlight hours of any other this year. File photo / Doug Sherring

You may be able to hit the garden after work or have a late dinner outside - today is the longest day of the year.

WeatherWatch said December 21 is summer solstice in New Zealand this year - meaning today has the most sunlight hours of any other this year.

In the lower South Island - where the days are at their longest in New Zealand - the sun is up for almost 16 hours.

"While technically the days do gradually start to get a little shorter in January the sunset times barely change," WeatherWatch analyst Philip Duncan said.

"This is the true start of summer - with the hottest weather coming over the next two months."

He said February was usually the hottest month, then March started to cool down.

"So - welcome to summer 2016, New Zealand."

Christmas Day weather was also looking good.

Duncan said a large high was approaching New Zealand.

There was a 20 per cent chance of showers early in the morning nationwide, mostly in western South Island areas. But they were likely to dry out after the sun comes up.

The chances of showers fell to about 5 per cent in the afternoon.

The warmest places to be were likely around Gisborne, Bay of Plenty, eastern Northland and the Coromandel Peninsula where highs may reach low to mid 20s.

The South Island was expected to be cooler. Dunedin may only reach a high in the low to mid teens, Christchurch the mid to late teens and Wellington late teens, Duncan said.

The south to southwest flow meant Southland may only reach 13C in the deep south but up to 20 in Central Otago.

The flow meant it may be cool, cloudy and brisk for those enjoying an outdoor Christmas lunch.

"Many want to know if the incoming high means you can have lunch or dinner outdoors," said Duncan.

"We're going with yes and no. The high coming in brings a bit of southwest flow to the country."

He said Auckland may be a "little windy" with a southwesterly around 30km/h.

"The kids may not care much but the parents or grandparents might."

Duncan said coastal areas of both islands may be exposed to cloudy areas and breezy colder winds. Neighbouring regions will be hot and sunny.

"The mountains and ranges make all the difference this wekeend and one slight change in the wind angle can make a big difference between whether or not it will be cloud-free or cloudy.

"It may be one of those decisions you can't make until the day itself - if you're a bit fussy about temperatures, wind or cloud cover that is."

He said sunburn was still a risk.

"Even in cloudy weather you can get sunburned. Be aware of the conditions - and remember if it's a cold day that makes zero difference on whether or not you can get UV damage to your skin."

Christmas temperatures

Whangarei
Christmas Eve: High 21C, low 14C
Christmas Day: High 22C, low 13C
Boxing Day: High 23C, low 13C

Auckland
Christmas Eve: High 20, low 15C
Christmas Day: High 19C, low 15C
Boxing Day: High 19, low 15C

Tauraunga:
Christmas Eve: High 23C, low 13C
Christmas Day: High 22C, low 13C
Boxing Day: High 23, low 13C

Rotorua
Christmas Eve: High 21C, low 10C
Christmas Day: High 21C, low 11C
Boxing Day: High 22C, low 11C

Napier
Christmas Eve: High 22C, low 12C
Christmas Day: High 24C, low 11C
Boxing Day: High 23C, low 12C

Wellington
Christmas Eve: High 18C, low 12C
Christmas Day: High 16C, low 13C
Boxing Day: High 16C, low 13C

Christchurch
Christmas Eve: High 20C, low 11C
Christmas Day: High 20C, low 10C
Boxing Day: High 21C, low 11C

Dunedin
Christmas Eve: High 20C, low 11C
Christmas Day: High 14C, low 10C
Boxing Day: High 16C, low 10C

- MetService