Weather: Northland in for heavy rain, showers forecast in Auckland, freezing temperatures in south

It’s set to bucket down in northern parts of the country this weekend, while most areas south of Auckland will see chilly yet sunny conditions.

MetService has issued a heavy rain watch for Northland between 8am today and 1am Monday. High rainfall rates there could cause streams and rivers to rise fast, surface flooding, landslips and dangerous driving conditions, the forecaster said.

Even with the highest temperature this morning, Kaitaia, sitting at 12.4C at 9am, had rain forecast for all day Saturday and Sunday. The daily high was expected to reach 14C, the same as Whangārei, where rain was also forecast.

The Northland Civil Defence Emergency Management Group has told residents to keep up to date with forecasts, take extra care while driving, and check and clear drains and gutters.

In Auckland, Saturday was expected to be partly cloudy with showers possible north of Whangaparāoa from the afternoon. MetService has forecast occasional rain for Sunday. Both days were tipped to reach 15C and fall to 7C at the coldest.

Heavy Rain Watch Updated 🟡🌧

Area: Northland
Period: 63hrs from 8am Fri, 2 Aug - 11pm Sun, 4 Aug

Forecast: Periods of heavy rain. Rainfall amounts may approach warning criteria in a few spots, especially about the eastern hills, today and Saturday morning. The heaviest falls… pic.twitter.com/3tzfXMfCfA

— MetService (@MetService) August 1, 2024

Showers were expected to linger about the city on Monday and Tuesday before drying out from Wednesday when it should settle into cloudy conditions.

Sub-zero temps in south

Almost everywhere south of Auckland began the weekend with frosts and mostly clear skies. MetService recorded sub-zero temperatures across the South Island this morning, falling as low as -10.7C at Mount Cook Airport.

St Arnaud dropped to -8C, Twizel to -7.7C, Dunedin Airport fell to -6.5C, Alexandra Airport to -5.2C and Christchurch Airport went to -5.1C, MetService said.

MetService meteorologist Alwyn Bakker said temperatures are colder than usual for this time of year due to a “sudden stratospheric warming” (SSW) event – a rare phenomenon that has only been observed three times in the satellite era in the Southern Hemisphere.

🩳 "Chuck on your shorts and jandals bro, it's -8.8 degrees outside!"

... is probably what people in Lake Tekapo township said waking up to this view today 😉

🧥 Jokes aside, it's going to be a chilly weekend for most of NZ, so do stay warm!

🥶 Some of the other coldest… pic.twitter.com/LpMVPgJc2K

— MetService (@MetService) August 2, 2024

This is combined with a ridge of high pressure clearing the skies overnight.

“So there’s a lot of heat loss happening overnight.”

Bakker urged those travelling to the ski fields to take extra care on the roads, as the lower temperatures will cause ice on the road to stick around for longer.

The National Institute of Water and Atmospheric Research (Niwa) explained the SSW event as an anomaly in wind patterns around Antarctica that usually keeps the harsh polar conditions away from New Zealand.

♻️ Every winter, the polar vortex, a ring of stormy weather, forms high above Antarctica in the stratosphere.

This year, the vortex is showing signs of warming & being disturbed 🐧

A disturbed vortex may contribute to stormier conditions in NZ & Australia in late July & August. pic.twitter.com/AUxVd60ytk

— NIWA Weather (@NiwaWeather) July 13, 2024

“Every winter, the polar vortex forms high above Antarctica in the polar stratosphere [the second-lowest layer of Earth’s atmosphere]. This year, the vortex is showing signs of being disturbed,” Niwa said.

“When an SSW occurs, it can help to weaken or displace the polar vortex in the stratosphere, which then filters down onto the tropospheric polar vortex [at the lowest layer of Earth’s atmosphere] and influences our weather patterns.”

Raphael Franks is an Auckland-based reporter who covers breaking news. He joined the Herald as a Te Rito cadet in 2022.