Cool change for South as polar jet stream bears down

While the heat has gone on for some in the South this week, another polar jet stream is set to barrel in, sending temperatures plummeting.

Parts of inland Otago have hit highs around 24degC in the past couple of days, but Niwa says a succession of cold fronts is going to move across the nation on Thursday and Friday, bringing rain or showers to many areas.

Niwa says the cold fronts are associated with another polar jet stream, which will lead to “chilly temperatures for the time of year” as we round the corner towards summer.

MetService shows Alexandra expecting highs of 26degC tomorrow and 22degC on Thursday before dropping to 14degC on Friday, with an overnight low of 4degC. Dunedin, meanwhile, looks set for 23degC tomorrow before dropping to 12degC on Friday and 13degC on Saturday.

MetService says there could even be snow to some parts of the South island on Friday.

The cool change looks short-lived, however, with temperatures heading up again over the weekend.

Meanwhile, it’s a wet week for the North Island, with rain expected this afternoon and evening as a result of surface wind convergence and daytime heating, according to MetService.

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

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 thunderstorms in the afternoon and evening is regarded as moderate in the inner parts of Southland, Clutha, Dunedin, North Otago, Central Otago, and the south of Canterbury near the alps. If a thunderstorm forms here, it may produce small hail and isolated heavy rain of 10 to 25 mm/h.

According to MetService models, a deep low may build east of the North Island late on Friday and Saturday. This will result in severe southwest gales from Wellington to Wairarapa and Hawke’s Bay on Saturday, as well as low confidence warning amounts of rain in Hawke’s Bay and southern Gisborne.

- ODT Online/NZ Herald