Weekend weather a triple threat’ for all
Metservice is warning travel disruptions are likely this weekend, as severe gales, heavy rain and big waves batter the country, followed by cold Antarctic air bringing snow to low levels in the deep south.
The snow is expected to be challenging for livestock in the South Island early next week.
A fast-moving low expected to brush past the bottom of the South Island early Sunday would be the lowest in New Zealand ‘‘for a long time’’, Metservice meteorologist Tom Adams said.
It would contribute to an unusually large pressure difference between Auckland and Invercargill, bringing gales to many parts of the country, including areas that don’t often see strong wind.
‘‘This is widespread severe weather. Localised severe weather has occurred many times over the last few years, but seldom affecting quite as much of the country as is forecast for this weekend,’’ Adams said.
He and his colleagues were ‘‘poring over their pressure charts in anticipation of one of the most widespread severe weather events this year’’.
While rain would be heavy in several locations, especially along the west of the South Island, it was the wind that had the greatest risk of causing widespread disruption during the weekend.
The band of rain would be short-lived for many northern and eastern places, and winds would start easing on Monday, but the sting in the tail would be cold Antarctic air, Adams said.
‘‘This will bring snow to low levels in the far south, and most alpine passes are expected to see snow. Even for the North Island we are currently forecasting a spring top-up for Ruapehu, and the possibility of snow on the Desert Road.
‘‘Additionally, a surge of southerly swell brings the risk of coastal inundation to coastal areas on both sides of the country.’’
The low pressure system was being deepened by a strong jet stream, and was expected to be around 970hpa when it passes the bottom of the South Island early Sunday.
Models were picking a pressure difference between Auckland and Invercargill of more than 35hpa at that time, Adams said.
It would be the first time since November 2018 that the difference had been more than 33hpa.
Metservice meteorologist Lewis Ferris said ex-tropical Cyclone Uesi, which reached New Zealand in mid-february 2020, had been about as deep as this weekend’s low was expected to be, but Uesi had only localised impacts.
‘‘This weekend we’re talking about widespread severe weather,’’ Ferris said.
The strong winds were the result of the difference in pressure between the low and a high to the northeast of New Zealand, which was expected to be around 1024hpa by the end of tomorrow.
‘‘That’s why we’re seeing such a huge pressure gradient between Invercargill and Auckland,’’ Ferris said.
‘‘It’s kind of like a triple threat situation. Before the rain really sets in we’re going to have strengthening northerlies, bringing basically gales to all of New Zealand.’’