Heavy rainfall is expected for the South Island from Thursday. Photo: Supplied / NIWA
Rain up to 40mm an hour and severe thunderstorms are threatening large swathes of the country, with forecasters issuing a glut of warnings and watches from Northland and much of the North Island, down to heavy rain expected in the South.
Parts of the South Island could see up to two months' worth of rainfall in a single afternoon, NIWA says.
National Institute of Water and Atmospheric Research (NIWA) forecaster Seth Carrier said Thursday would see "a plume of moisture coming down from the north", carrying heavy rain that could impact the Bay of Plenty and East Cape, before the heavier rain crops up in the South Island.
"As we go into the afternoon, our attention shifts to the South Island - most notably far southern Canterbury, eastern Otago and eastern portions of Southland. As we go through the afternoon and evening, periods of moderate to briefly heavy rain affecting those portions of the South Island - and that is a concern because that area typically sees quite a bit less rainfall than other parts of the country."
In the North Island, Carrier said rainfall could exceed 100 millimetres, but in those South Island areas, rainfall of up to 150mm was possible.
"100mm of rainfall could be more than a month's worth of rain for these areas, and if we get up to 150mm - which is possible - that could be more than two months of rainfall for these areas so it certainly does increase the flooding threat for that part of the South Island as we go through Thursday and into Friday as well."
⚠️ Seth has a weather update about the incoming heavy rain.
— NIWA Weather (@NiwaWeather) October 2, 2024
In Otago, one to two months' worth of rain may fall in the east, possibly leading to flooding! pic.twitter.com/582FdxmzvG
Carrier said those downpours could result in South Island rivers rising rapidly.
MetService forecasters also issued a glut of heavy weather warnings and watches, including severe thunderstorm watches and particularly heavy rain on the way for many parts of the country.
"Almost all parts of the country can expect wet weather by the end of Friday, with heavy rain for some," a spokesperson said.
Warnings and watches for heavy downpours in Northland, Auckland, Waikato, Bay of Plenty, East Coast, Hawke's Bay, Taupō, Taranaki
Thunderstorms could bring downpours as heavy as 40mm an hour to Northland and Auckland, until early Thursday, and to Waikato, Coromandel Peninsula, Bay of Plenty, Rotorua, Taupō, Gisborne and Hawke's Bay from the early hours to mid-morning on Thursday, where strong wind gusts that could reach 110km/h or stronger.
This type of intense deluge could cause slips, surface flooding and flash floods, while strong gusts in that range could make driving hazardous and cause structural damage - including to trees and power lines, MetService said.
MetService said up to 110mm of rain could fall until 6pm Thursday about the ranges in Bay of Plenty, from Whakatane eastward, and for Gisborne-Tairāwhiti, north of Ruatoria, with lesser amounts closer to the coast. And before 8am Thursday up to 90mm of rain could fall on the Coromandel Peninsula.
Forecasters said the heavy rain was likely to continue longer over the northern Gisborne area, into Friday morning.
And the Taranaki Maunga area also received an orange heavy rain warning, as it could receive up to 110 mm of rain into Thursday morning, on top of what had already fallen, at a rate of up 25 mm an hour.
What's on the way this week?
— MetService (@MetService) October 1, 2024
Plenty!️ Almost all parts of the country can expect wet weather by the end of Friday, with heavy rain for some
Keep an eye on places like Southland and coastal Otago, which could also see a damp few days ahead pic.twitter.com/lhTVFRzPEc
"A series of active fronts preceded by a strong and moist northeast flow move onto northern parts of the North Island from this afternoon, reaching Auckland tonight," MetService said.
"About Northland and Auckland (including Great Barrier Island), there is a moderate risk of some thunderstorms being severe between 8pm Wednesday and 5am Thursday, producing localised downpours of 25 to 40 mm/h. This risk should ease in Northland around 2am."
"Note, these downpours could occur with or without thunderstorms."
Kia ora Aucklanders, our friends @MetService have issued a severe thunderstorm watch for Auckland, including Great Barrier Island ⛈️, as well as a strong wind watch for Great Barrier Island ️. Please keep an eye out on the latest information on MetService's website. https://t.co/tNdTZAFw7c
— Auckland Emergency Management (AEM) (@AucklandCDEM) October 1, 2024
MetService advised locals to clear gutters, avoid low-lying areas and drive cautiously.
"The school holidays started out nice and bright, but things do take a turn today and into Thursday," MetService meteorologist Mathapelo Makabulane told Morning Report on Wednesday.
"For the North Island, we're also expecting things to get progressively wetter, especially in the northern half of the North Island and then eventually quite wet conditions for places like Northland, Coromandel and the Bay of Plenty into Thursday."
In the south, heavy rain warnings were in place for Tasman, northwest of Motueka - with up to 160mm expected - and the Richmond and Bryant Ranges, including the Rai Valley, where 110m might fall. Both areas could have their orange warnings upgraded to red.
"So today we're expecting - especially for the South Island - some wet weather to start coming on, especially in those western parts," Makabulane said. "But that does spread across the island even reaching the eastern parts, places like Canterbury, Otago later on this evening and into tomorrow....
"The heaviest rain is expected in the mountainous areas, but places away from the ranges can also expect quite wet weather."
A heavy rain watch was in place for the Buller and Grey districts for Wednesday, with downpours particularly expected about the Paparoa Ranges.
While Westland looked set for the heaviest rain nationwide, with up to 200mm expected about the ranges, and a bit less closer the coast, though that warning was lifted by MetService late Wednesday.
"Peak rates of 15 to 20mm/h expected about the ranges from late Wednesday morning to early Wednesday evening."
Central Otago and Queenstown Lakes could expect heavy snow above 700m.
"It seems like we've had quite a few snowfall events lately and yes, the latest one is expected for the inland part of Otago - so that includes the Southland, the Queenstown Lakes District as well, and we're looking at that from this afternoon onwards into the evening as well," Makabulane said.
North Otago, Dunedin and Clutha residents should expect heavy rain possibly exceeding warning criteria for a whopping 33 hours from 3am Thursday, with a high chance the situation will be upgraded to warning level.
And finally, the northern half of Southland should expect periods of heavy rain from 9am Thursday, with a chance it will last into the night and possibly upgraded to a warning.
"Once this band of rain moves through, the good news for the North Island is that things look like they clear up pretty quickly… All in all it looks like Friday, we could see some bright spots for most of the country," Makabulane said.
'Drive to the conditions'
Waka Kotahi / NZ Transport Agency Waka Kotahi warned school holiday travellers to take care, saying some might not expect snow on the roads this late in the year.
"We always do get a few short, sharp blasts," said journey manager Tresca Forrester.
"Everything sort of happens today into the early hours of tomorrow. So if you are travelling, it would pay to just check probably two things: the MetService has really great forecasting and warnings in place… and also our journey planner,which is obviously the source of truth for 24/7 for our road closures, et cetera.
"At the moment every road is open except for the Milford Road [SH94], so that's down to the Milford Sound there, and that is closed due to snow at the moment."
It also remained "avalanche season" in that area, Forrester said.
"That actually is why the road is closed here this morning, and they're expecting an update around sort of midday."
In areas where rain was expected, she said to be aware of "small slips, rocks, things like that".
"Drive to the conditions. - so if it is streaming down with rain, it's just what you're feeling comfortable and safe with, and just take it easy, you know? Take your time. You might have a car full of kids, but you know just stop into those awesome local cafes along the way and get a cuppa."
