Weather: Thunderstorms possible for much of the country today

A strong and unstable westerly flow will cover the country tomorrow morning, with embedded troughs bringing bands of rain or showers to many regions. Photo / Niwa

Forecasters are warning that swathes of the country could be hit by thunderstorms today, accompanied by heavy rain, hail and strong wind.

Unsettled weather is forecast across the country this week, with a strong and unstable westerly flow bringing bands of rain to many regions, and snow to areas in the South Island.

Several strong wind watches were issued yesterday for Northland, Coromandel and Auckland, with high winds causing two lanes on Auckland's harbour bridge to close in the afternoon.

🌀A small but noticeable area of low pressure is moving through Cook Strait right now, as seen on the @MetService rain radar.

Track Here: https://t.co/sZ6VGec556 pic.twitter.com/hUnGhSeQbs

— WeatherWatch.co.nz (@WeatherWatchNZ) September 12, 2022

There is a risk of thunderstorms today for northern parts of the North Island, however that risk will diminish by the end of the day.

"Any thunderstorms that occur will bring brief heavy rain, small hail, and squally wind gusts of 80-90km/h," the MetService reported.

Taranaki, Waitomo and Taumarunui may also see thunderstorms during the afternoon. potentially continuing into the night.

For the South Island, there is a moderate risk of thunderstorms from the west of the Tasman District to Fiordland including the adjacent Southern Alps, the MetService says.

⛈ Thunderstorms Tomorrow ⛈

The atmosphere will be pretty unstable tomorrow, especially over Te Waipounamu/South Island.

Westland, Fiordland, and the coast of Southland have a high risk of thunderstorms in the morning ⛈

For more details, head to https://t.co/BZWb807s5l pic.twitter.com/bYZd9wG9Yz

— MetService (@MetService) September 12, 2022

There is also a moderate risk of thunderstorms for North Otago and eastern parts of Canterbury during the afternoon and evening as a southerly wind change moves northwards, with a lower thunderstorm risk for inland parts of Otago, Canterbury and the Kaikōura Coast.

MetService meteorologist Alwyn Bakker said this was due to a trough of low pressure that moved eastward over the country yesterday and would continue today, bringing showery conditions in its wake.

It will also bring cold temperatures as it makes its way over the higher level of the South Island.

"The cooling effect will be less noticeable at ground level, but the resulting atmospheric instability makes thunderstorms more likely, and snow is expected to 300-400m in the south on Tuesday," Bakker said.

As the week progresses, frosty conditions will continue to put a damper on spring for southern and central parts of the North Island, dusting Mount Taranaki and parts of the central plateau with a layer of snow.