MetService is warning the storms could create flash flooding and make driving conditions hazardous.
A Severe Thunderstorm Watch is in force for localised downpours in South Waikato, inland Bay of Plenty/Rotorua, Taupō, southern Gisborne/Tairawhiti, and Hawke’s Bay this afternoon and evening.
This severe weather will be followed by extreme winds in the upper North Island this weekend.
Niwa Weather meteorologist Ben Noll said the front would be pushed up by a “resurgence” of the polar jet stream: a band of fast-flowing, narrow air currents circulating high in the atmosphere to our south.
“The polar jet starts to develop this week in the Australian Bight south of Tasmania, and then a piece of that moves right into New Zealand, and across the country, on Saturday,” Noll said.
The weather pattern may bring large waves, chilly temperatures, and low snow levels to the south, and strong southwesterly winds on Saturday, especially in Auckland and the northern North Island.
Before the wind begins to gust, Auckland could be hit with thunderstorms as a front in the Tasman Sea approaches the northern North Island on Wednesday evening.
“By Friday a new low in the Southern Ocean will work with a high-pressure zone in the south-eastern corner of Australia to drive in a burst of gale-force westerlies up the South Island and into the North Island.
“By Saturday those winds spread as far north as Auckland City with gusts over 100km/h possible. In true spring style, it all blows through fast though.”
“There is an associated low risk of a few thunderstorms about Northland, Auckland and western parts of Waikato,” MetService reported.
MetService warned of the severe weather on their website, explaining they are mostly confident of the severe west to southwest gales for Northland, Great Barrier Island, Auckland, Waikato, Coromandel Peninsula and western Bay of Plenty.
“There is also moderate confidence of severe southwest gales for Mahia Peninsula and near the coast of Tairawhiti/Gisborne,” MetService wrote.
MetService already has road snowfall warnings in place for the Lewis and Porters Passes (State Highway 73), Lewis Pass (SH7) and the Desert Rd until Wednesday morning.
It comes at the end of an extremely windy month, which has downed trees and powerlines, and nearly a new national record with a 246km/h gust measured at Cape Turnagain on September 17.
Noll said only last Thursday Wairoa set a new North Island record for the hottest temperature – 29.6C - ever measured in September.
“At a wider level, this is indicative of the types of patterns that can happen in spring – but especially one with a burgeoning strong El Niño – where we see these very changeable patterns from one week to the next,” he said.
“So, here in September, you can go from island-wide record maximum temperatures to having a resurgence of the polar jet stream – and that can be quite jarring.”
