Orange heavy rain warnings are in place for the north and west of the South Island, and watches are in place for parts of the North Island on Sunday.
MetService said an active front, preceded by a strong moist northerly flow, was expected to move over the country from the west during Sunday and Monday, followed by a broad trough of low pressure that would bring rain to central and northern parts of the country.
"Over the Tasman sea, this next area of low pressure brings us some wetter and windier weather... as we head in towards Sunday, especially for places like the western coast down through the South Island, parts of the Tasman area," MetService meteorologist John Law said.
"Even as we head towards the end of the day on Sunday, this wet weather transfers across towards the North Island and accompanied by some pretty strong winds."
The difference between the low-pressure system on the west and high-pressure system on the east would also "drive... winds across the country", he said.
Heavy rain warnings have been issued for Tasman northwest of Motueka from 11am, the Paparoa Range and the ranges of the Buller District from 2pm and the ranges of Westland from 9am on Sunday.
There could be up to 150mm of rain in the Tasman ranges with up to 60mm closer to the coast, said MetService.
Westland could also see up to 140mm of rain with peak rates of up to 25mm per hour in possible thunderstorms.
Heavy rain watches were also in place for the Canterbury high country from 11am, the Richmond and Bryant Ranges from 1pm, Mount Taranaki from 2pm, and the Tararua Ranges from 11pm on Sunday.
MetService warned that heavy rain could cause streams and rivers to rise rapidly.
Surface flooding and slips were also possible and driving conditions could be hazardous.
