A severe weather watch is in place for eastern areas of both islands over the weekend.
MetService says the heaviest rain is likely to be in the upper east coast of the South Island, including Marlborough and Kaikoura, and the east coast of the North Island from Wellington north to the Bay of Plenty.
The rain is likely to start overnight for the affected northern areas, and early tomorrow afternoon for the south.
Unsettled upper South Island and North Island on Friday-Saturday ️— NIWA Weather (@NiwaWeather) April 4, 2019
Pockets of rain, some heavy, will be about. Not all bad news -- the Wairarapa & upper North Island could use some moisture!
Plan around it with NIWA's hi-res model pic.twitter.com/4phWNfIPa0
MetService said a slow moving trough of low pressure is forecast to affect New Zealand until early Monday.
"At this stage, the threat of heaviest rain is in eastern Marlborough especially the Kaikoura Coast, southern Wairarapa, the eastern hills of Wellington, Coromandel Peninsula and Bay of Plenty west of Te Puke," it said.
Centers including Auckland, Christchurch and Whangarei are also forecast to get rain over the weekend.
There's good news for the West Coast however, with sun forecast for the weekend. Otago is also looking fine with the possibility of some morning frosts.