MetService meteorologist Andy Best said aside from some isolated showers across the country, the weekend was not looking too bad.
A ridge of high pressure was bringing fine weather for most places, while a low-pressure system would bring some bands of rain to the eastern North Island.
However, a strong to gale west to southwest flow would persist over most of the country, keeping temperatures on the cool side.
Rain was forecast for the West Coast of the South Island Sunday through Monday as a front made its way north.
A second front was forecast to move north across the South Island late Monday and the North Island on Tuesday bringing another period of rain.
A ridge was then expected to extend onto the South Island from the Tasman Sea late Tuesday then move onto the North Island on Wednesday as another front approached the South Island from the southwest.
Brandolino said from midweek a rare phenomenon known as a sudden stratospheric warming (SSW) event could take place.
Importantly, it had the potential to mess with a ring of stormy and freezing weather that encircles Antarctica, which was at its strongest at this time of year – and which was known better as the polar vortex dubbed the "beast from the east" - threatening to send a series of cold blasts from the North Pole to Western Europe and the UK, along with the east coast of the United States.
While this swirling, freezing air mass was usually effective at keeping harsh, wintry conditions locked up close to the pole, an SSW could help weaken or displace it in the stratosphere.
This sent those cold masses filtering down on to the tropospheric polar vortex, potentially influencing our own weather patterns.
So far, the timing of this event was very uncertain, Brandolino said.
"It is forecast to happen from midweek, but then there is a lag between when it occurs and further flow-on effects. It is occurring 50km up, so it could take weeks before we see any impacts on our weather."
Exactly where the impacts would fall was also very uncertain.
"The Southern Hemisphere is a huge area, and Aotearoa is tiny in comparison. It could completely miss us, but the signs are we are in for some pretty active weather from mid-September into October."
For New Zealand, such events were extremely rare. There had been only two in New Zealand in recorded times, or since the late 1950s - one in September 2002 and the other in September 2010.
After the SSW in 2002, New Zealand experienced its coldest October in 20 years with below-average temperatures covering much of the country and frequent ground frosts.
In 2010 – which was classed as a minor event – a number of rainfall records were broken with well below normal sunshine and very cold temperatures in parts of the South Island.
Today's weather
Whangārei Morning shower or two. Southwesterlies. 16C high, 10C overnight.
Auckland Mainly fine, a few showers this evening. Southwesterlies, strong from afternoon. 15C high, 11C overnight.
Hamilton Fine. Southwesterlies. 15C high, 8C overnight.
Tauranga Fine. Southwesterlies. 16C high, 9C overnight.
New Plymouth Mainly fine, chance shower. Southwesterlies. 15C high, 9C overnight.
Napier Cloudy periods and chance shower, then becoming fine afternoon. Southerlies. 15C high, 5C overnight.
Whanganui Fine apart from chance morning shower. Southwesterlies. 14C high, 8C overnight.
Wellington A few morning showers, then fine. Fresh southerlies easing, turning northwest evening. 11C high, 6C overnight.
Nelson Fine. Southwesterlies. 15C high, 6C overnight.
Christchurch Fine. Light winds. 13C high, 1C overnight.
Dunedin Fine. Winds tending northwesterly in the morning. 14C high, 6C overnight.
