Auckland gets 24 straight days of rain

Auckland's run of wet weather could soon be one for the record books.

Rain has fallen on each of the 24 days of August so far.

And the sodden period may continue as a rare weather event forecast to start over the next week will potentially bring a wild September and October.

Niwa meteorologist Chris Brandolino said the current rainy period was closing in on the record of 28 days consecutive days in a month in which more than 0.1mm of rain has been recorded at its Māngere station.

But while some potential showers forecast tomorrow and Monday could take the tally to 26 days, fine weather on Tuesday and Wednesday could dry up the possibility of making history.

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 on to the South Island from the Tasman Sea late on Tuesday then move on to 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 low temperatures in parts of the South Island.

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