Up to 400mm of rain could hit parts of the South Island as the second of two weather systems bears down on the country.
A front moved northwards over the South Island yesterday and was set to continue today, while the second system is expected tomorrow, bringing further heavy rain, strong winds and large wave conditions.
MetService said heavy rain was expected for most of the West Coast starting this morning and continuing through until Friday or Saturday.
There was a risk of surface flooding and slips on much of the West Coast, MetService meteorologist Alanna Burrows said.
She said people should avoid low-lying areas and drive cautiously on the roads.
The areas likely to experience the heaviest rain on Thursday would be Westland and the Tasman District, Burrows said.
The Tasman district could see up to 400mm, which was a "huge" amount of rain, while Westland was looking at between 500mm and 600mm for the combined events.
Orange heavy rain warnings, updated late on Thursday morning, were in place for Tasman District northwest of Motueka, Buller District, The Nelson and Marlborough Ranges, Grey District, Westland District, and the headwaters of the Canterbury lakes and rivers.
There are orange strong wind warnings for many areas of the upper South Island and the Wellington region of the North Island.
There is also a heavy rain watch for Southland, for 11 hours from 4pm on Friday.
NZ Transport Agency Waka Kotahi warned motorists to prepare for difficult driving conditions.
Along with the heavy rain, the lower North Island could expect severe gales on Friday in Wellington and Taranaki, Burrows said.
Things would ease off on Sunday, she said.
- additional reporting Allied Media
