Weather: The polar jet stream is heading our way after a rainy week towards the North Island

As we head into summer, the last of the cold temperatures won’t go away without a fight as another polar jet stream heads our way this weekend.

It’s a wet week for the North Island with rain expected this afternoon and evening due to the convergence of surface winds and daytime heating, according to MetSerice.

There is a moderate possibility of thunderstorms in the afternoon and evening in Auckland, mostly south of the city, the Bay of Plenty near west Tauranga, Waikato, west Waitomo and the Coromandel Peninsula.

There is a lower chance of thunderstorms in the north across the rest of Auckland and eastern Northland, and in the south over North Taranaki and Taumarunui, along with the rest of Waitomo. If these thunderstorms form, they will produce between 10 to 25 mm/hour of locally heavy rainfall.

For the South Island, the majority of Otago, Southland, the high hills of Canterbury and the Nelson Lakes are all at low risk of thunderstorm activity. However, the chance of afternoon and evening thunderstorms is moderate in inland parts of Southland, Clutha, Dunedin, North Otago, Central Otago and South Canterbury near the Alps. If a thunderstorm forms here, it may produce small hail and isolated downpours between 10 and 25 mm/hour.

Until Wednesday, onshore winds will continue to affect eastern parts of the North Island, leading to cloudy days with heavier rain on higher ground.

A light breeze and sunny skies are expected over the upper half of the North Island and inland areas of the South Island this week. However, showers may occur in the afternoon, possibly with the possibility of thunderstorms.

Most temperatures this week will be pleasant. The temperature in Christchurch on Thursday is expected to reach 26C, which is about 6C warmer than the usual maximum temperature for this time of year. But due to a wave of cold air coming in from the Southern Ocean, we expect the temperature to reach 14°C on Friday, so Cantabrians don’t give up their coats and jackets just yet.

On Wednesday, rain begins to fall in Fiordland, indicating the approach of cold air. This band of rain advances quickly to the north on Thursday and then across the North Island on Friday. This system leads to significant drops in temperatures, sudden heavy rains, and sometimes strong southerly winds.

On Thursday and Friday, a series of cold fronts move across the country, bringing rain or showers to many areas.

Niwa reported that the cold front is another polar jet stream, which will bring “cold temperatures for this time of year” as we head into summer.

According to MetService models, a deep low may form east of the North Island late Friday and Saturday. This will bring severe southwesterly gusts from Wellington to the Wairarapa and Hawke’s Bay on Saturday, as well as a low rainfall warning for Hawke’s Bay and south of Gisborne.