Wet weather ahead as low that caused big Oz storm arrives

Heavy rain is possible for Auckland tomorrow, as a low-pressure system swings into the country today. Photo / Alex Burton

The same low pressure system that brought snow to Australia last week is wheeling into New Zealand – but now it's packing a much milder, albeit wetter, flavour.

A meteorologist says the system won't have the chill factor which delivered the unusual sight of snow to New South Wales last week, but was still expected to bring heavy rain to parts of the country over the next 24 hours - with more wet days coming next week.

MetService has issued heavy rain warnings for much of the South Island's west coast today and into the early hours, while a heavy rain watch is in place for the ranges of Buller and Nelson west of Motueka, from 3pm to midnight.

Heavy northerly rain was also possible overnight across Taranaki north and east of the mountain, along with Waitomo and the Central North Island – as well as later, in the ranges of Bay of Plenty east of Whakatane, over 24 hours from 3pm tomorrow.

The Heavy Rain Watches & Warnings have been updated with the addition of northern Taranaki, Waitomo, Taumaranui, Tongariro NP and eastern ranges of Bay of Plenty starting Monday as this rain system makes it's way north. More at https://t.co/qHyE5zhh6X ^AC pic.twitter.com/nBvpewdGrC

— MetService (@MetService) June 12, 2021

That came as a complex, slow-moving low moved across the country – beginning with a front drifting across the east of the South Island today.

Most centres across the North Island were in for a wet start to the week – with periods of heavy rain possible for places including Auckland, Hamilton and New Plymouth tomorrow.

MetService forecaster April Clark said this was the same system the caused havoc across the Tasman last week, "but it's not going to have the same effects".

"We are actually not looking at really cold temperatures, but above average ones – especially overnight and for the next couple of days," she said.

"There'll be a lot of moisture – but there's also a huge amount of cloud around, which is the main reason we are seeing warmer-than-average temperatures in general."

WV satellite imagery displays moisture content in the mid & upper atmosphere. More moisture indicated by greens/whites = greater potential for rain making. Spot the area of high moisture funneling into the West Coast/Fiordland where Heavy Rain Watches/Warnings are now in place^AC pic.twitter.com/EcuPfud6mS

— MetService (@MetService) June 12, 2021

Clark explained that low-pressure systems typically came with northerly fronts ahead of them, and southerly winds behind them.

"So right now we are seeing the eastern edge of that northerly – but what Australia has been seeing is the southerly," she said.

"While the low will move across us early-to-mid next week, we aren't getting that really good southerly flow with it, because the low is changing in its nature."

Clark said the system was also much different from the last big visiting low, which caused widespread flooding across Canterbury at the start of the month.

"This one isn't as strong, it doesn't have the same orientation, and it's very slow moving."

Niwa forecaster Ben Noll said the arriving system was consistent with Niwa's outlook for the winter – which had a theme of dry spells interrupted by sometimes-major pulses of rainfall.

That was partly due to built-up heat still lingering in the western Pacific, which could result in subtropical moisture being fed into nearby low-pressure systems – as happened with the Canterbury storm.

The warmth had been left over from a now-faded La Nina climate system and, with no such big driver influencing our weather, New Zealand could continue to see intermittent large downpours for at least the next few months.

"There's an expectation that things will be a little more variable," he said.

That's a lot of rain! 🌧

📊 Our modelling suggests over 200 mm is possible for much of the western slopes of the Southern Alps by midnight Monday. pic.twitter.com/qAQAHh4BiT

— NIWA Weather (@NiwaWeather) June 12, 2021

"But so far, June has had some temperatures that in some instances have been more like mid-autumn.

"That looks to persist at some level for next week, although it's not going to be quite as warm as last week.

"Then, to round out the month, over the last week or so of June, it's going to cool down to something more typical for this time of year.

"However, the flavour of this winter isn't for these long-lasting cold periods, which will quickly be replaced by milder air overall. For keen skiers and snowboarders, that's not necessarily good news."