Heavy rain warnings have been issued for Bay of Plenty early on Tuesday, with further falls for northern Westland, Buller and the extreme western ranges of Nelson until Wednesday.
The MetService says a front is forecast to move through Bay of Plenty, with 90 millimetres expected in the eastern ranges.
It says up to 140 millimetres could fall in the Nelson ranges by Wednesday, while the coastal areas of northern Westland and Buller may get about 60 millimetres.
Rivers and streams in all these areas may rise rapidly and there could be surface flooding and slips.
Alpine passes closed
Snow has closed Arthur's and Porters passes on State Highway 73 in the central South Island.
Five to 10 centimetres is expected to fall in both passes overnight on Monday.
Snow is forecast down to 400 metres in the Canterbury foothills and possibly Banks Peninsula.
On the West Coast, drivers of high-sided vehicles are advised take care due to high winds on State Highway 6 between Harihari and Haast.
Delays are also likely between Haast to Hawea - the Haast Pass - due to a slip.