The tropically charged storm was expected to also pummel both islands with severe thunderstorms throughout today.
MetService has issued heavy rain warnings from Northland to Fiordland, and rain watches for the Bay of Plenty and the Tasman regions.
The worst is expected in Northland, where up to 130 millimetres of rain could fall over 27 hours; Taranaki, where 450mm could fall in 39 hours; and Nelson and Marlborough, where 300mm could fall in 42 hours.
The warning for Northland lasts from midday Wednesday to 3pm on Thursday. With 40mm of rain an hour possible, streams and rivers could rise quickly and cause slips.
In Taranaki, MetService’s warning is from 2pm today until 5am on Friday, when 35mm of rain an hour might be possible. The most rain is likely on Mt Taranaki itself.
In Nelson and Marlborough, the rain is expected to come later; the warning spans from 9pm on Thursday until 3pm on Saturday. Most rain is tipped to fall about the Richmond and Bryant ranges.
In Auckland, meanwhile, thunderstorms pose a risk for the city along with periods of heavy rain. The worst of the weather is set to skip the city, however, with no warnings or watches in place for the region.
Heavy humidity is plaguing the city and is expected to make for hot and sticky evenings.
More rain warnings extend down the western coasts of both islands, with a warning for Wellington to Horowhenua, Westland south of Otira and Fiordland north of Doubtful Sound.
Periods of heavy rain will lash Bay of Plenty, Tasman northwest of Motueka and Buller south of Karamea, where deluges could reach warning criteria and heavy rain watches have been issued.
MetService meteorologist Dan Corrigan has told people to pay close attention to forecasts as their severe weather warnings could change as the storm evolves.
“MetService is keeping a close eye on this rain band, but there is still some uncertainty surrounding the details of when and where the heaviest rain will fall later this week,” Corrigan said.
The storm has boomeranged back on the country after dumping heavy rain in Northland and Coromandel earlier this week.
The low-pressure system has rolled over the country from the Tasman Sea, picking up and bringing lots of warm air and water.
Corrigan said a stubborn high-pressure system off New Zealand’s east coast was stopping the storm from following its normal path away from the country.
The humid, unsettled northerly flow was expected to affect the country until at least early next week, with multiple fronts embedded in the system likely to bring more rain.
