Swathes of the South Island are set to be soaked in the coming days, with torrential rain expected to drench western regions.
Although the end of the long weekend is looking mostly settled, with warmer-than-average temperatures forecast for much of the country on Monday, substantial rainfall is imminent. The summer sun is under siege by a "complex frontal system", according to MetService, spelling a period of heavy rain for the west of the South Island.
Severe weather warnings have been issued for both Fiordland and the Westland ranges, with a heavy rain watch also set for two national parks on the upper west coast.
Between 70 and 90mm of rain may accumulate in the Fiordland region, spanning northwards from Doubtful Sound.
"Heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous," MetService said on Monday morning.
The warning is tentatively set from 10pm on Monday to 10am on Tuesday.
The Westland ranges, south of Otira, are also in for a drenching on Tuesday, with a warning in place between 4am and 9pm. MetService is expecting 120 to 160mm of rain to accumulate, with peak rates of 20 to 30mm/h.
The downpour may cause surface flooding and slips in the region, with motorists advised to expect dangerous driving conditions.
A heavy rain watch has also been issued for the Buller and Nelson ranges, particularly for Kahurangi and Nelson Lakes National Parks.
The deluge is forecast to hit on Tuesday afternoon and may continue into the night, with rainfall possibly reaching warning criteria.
However, the eastern regions aren't exempt from the downpour, with Otago and South Canterbury also "set to be significantly soaked" this week, according to MetService, with patchy rain spilling into Southland over the coming days.
Severe gales may also hit exposed parts of Canterbury High Country, Marlborough, Wellington and southern Wairarapa on Tuesday and early Wednesday.
A "complex frontal system" is to blame for the unwelcome change in conditions, MetService said on Sunday afternoon. The system, set to move east over the South Island from the Tasman Sea beginning on Monday night, will deliver the period of heavy rainfall to the South Island's west coast.
"The front should then weaken as it moves east across the North Island during Wednesday, while a low affects the south of the South Island," the service explained.
"The low should move away to the east early Thursday. Late Thursday, a southwest flow should lie over the country and gradually ease."
However, a ridge of high pressure is expected to settle over the country on Friday, spelling a return to fine, warm weather.