Heavy rain is set to lash parts of the South Island for much of the day, followed by more wet weather into next week.
Orange level warnings are in place for Westland and Buller districts until Friday evening.
MetService's Heath Gullery told RNZ's Morning Report programme the rain was starting in the west of the South Island and would slowly move up to the lower North Island throughout the day.
"There is likely to be some localised flooding, and rivers and streams will be running high."
Meanwhile, part of State Highway 73, between Arthur's Pass Village and Otira, is closed due to rockfall and will not reopen until some time on Saturday, NZ Transport Agency/Waka Kotahi advised.
There is a detour via the Lewis Pass (SH7), which adds about an hour to the trip between Christchurch and the West Coast, RNZ reported.
In Westland, between 70mm to 100 mm of rain was forecast about the ranges on top of what had already fallen, and 50mm to 80mm nearer the coast. Peak rates of 15 to 25 mm/h were expected about the ranges and thunderstorms were also possible.
Further heavy rain in Westland was likely on Sunday.
In the Buller district, between 70 to 90mm of rain, mostly about the ranges was expected until 8pm today, with peak intensities of 10 to 15 mm/h.
Heavy rain warnings for Tasman at the top of the South Island and the Tararua Range and Mt Taranaki in the North Island have been upgraded to orange.
People were advised to clear drains and gutters, avoid low-lying areas and to drive cautiously.
Once the current rain front moved away, there was more wet weather behind it until Tuesday next week, Gullery said.
But temperatures would be more mild - the east of the North Island could possibly reach the low 20degCs.
"It's a change from that really cold weather we've had... It certainly will feel spring-like."
Heavy rain watches were in force for the Grey District on the West Coast until 7pm today and for Fiordland, about and north of Doubtful Sound, in Southland from 11pm on Saturday until 7pm on Sunday.
Meanwhile, strong wind watches are in place for the Canterbury High Country until 5pm today, where northwest winds may approach severe gale in exposed places, and Wellington from noon until 1am on Saturday.
The heavy rain might be some good news for hydro lake levels which have been blamed for soaring power prices.
"I think it will, it will be a gradual impact... it'll probably take several rain events to bring those levels up again," Gullery said.
- additional reporting ODT Online
