A "significant low" set to loop back over the East Coast is shaping into a long spell of severe weather – with forecasters warning of heavy rain, damaging winds and large swells as the system circles back over the North Island in an unusual atmospheric setup.
The deepening low will stall, strengthen, and then swing back towards Gisborne, Hawke's Bay and the Eastern Bay of Plenty on Sunday.
Meteorologists say the pattern — where a low becomes trapped between two blocking highs and loops back over the same regions — is uncommon for New Zealand.
Erin Conroy provides an update on the latest weather impacting the central and east coast of the North Island. (Source: 1News)
Ōtorohanga District declared an overnight local State of Emergency after being hit by widespread flooding, slips, and heavy rain on Friday night into Saturday, with one man found dead after his vehicle was submerged in floodwaters between Pirongia and Ōtorohanga.
Follow 1News live updates here on the weather event here.
MetService has issued orange-level heavy rain warnings for the Bay of Plenty east of Ōpōtiki, Gisborne, and inland Whanganui, Manawatū north of Marton, and Taihape.
Orange-level strong wind warnings were also in place for Gisborne, Wellington, Wairarapa, Tararua, and eastern Marlborough.
Heavy rain watches covered Hawke's Bay, Wairarapa, Tararua and Wellington. Manawatū, Taihape, Whanganui, Horowhenua and the Kāpiti Coast were also under a strong wind watch.
Drone captures scale of damage after Ōtorohanga 'weather bomb' - Watch on TVNZ+
'Interesting setup'
MetService meteorologist Devlin Lynden told 1News the system was an "interesting setup" that did not occur often.
He said the weather system began with a cold front that moved east across the country on Thursday and Friday, bringing heavy rain to parts of both islands.
As that front passed, it interacted with a developing low-pressure system.
"What's happened is, there's also this low feature that's just northeast, and those have started to combine, and that cold front that's moved past has given this low pressure system the extra kick it needs to deepen."
The low was now becoming squeezed between two ridges of high pressure, Lynden said — one in the Tasman Sea and another far to the east of New Zealand.
"Those ridges to the west and east really stay pretty stagnant. They don't move and it allows this low pressure system to just sit in the same spot for an extended period of time and gradually move south.
"It's a very prolonged period of these strong southerlies into East Coast areas accompanied by periods of heavy rain."
Upper atmosphere dynamics were also helping support and hold the system in place.
While the low was strengthening due to the cold front, the air mass feeding it was coming from much further north.
"The origin of the air mass is from tropical regions, which is why it's been warm and humid," Lynden said.
"That moist air gets sucked into the cyclonic flow and pushed into the East Coast, and that's why we're expecting such large accumulations of rain."
NIWA said climate change had led to more intense storm events – with a warmer atmosphere holding more moisture, providing fuel for storms and increased wind speeds.
Regions in line for 'heavy, persistent rain and wind' from 'tropical rainmaker' - Watch on TVNZ+
'Weather fire hose'
1News meteorologist Dan Corbett said the system was a rare and volatile combination of ingredients, describing it as a "fire hose" aimed squarely at the North Island's East Coast.
"Think of having a big fire hose and spraying it in one location for a long time," he said.
"Then you turn around and spray the other side. Then you switch on the wind machine. Bring all that together and you get quite a nasty spell."
As the low stalled and looped back, it would repeatedly funnel tropical moisture into the same regions.
"When you're sitting there spraying that tropical moisture at one place — Gisborne, Hawke's Bay, Eastern Bay of Plenty — that means a lot of rain," Corbett said.
"Then you add winds, you add increased swell up to 6m in places… you've got the risk of disruption and, of course, a lot of moisture."
He said the first fronts may clear and gave the false impression the worst had passed.
"You think we're done — but then the low winds in, grabs that extra energy, deepens, and the blue comes back," he said.
"It's literally going into almost the middle of next week before the low finally moves away."
SHARE ME