Orange heavy rain warnings have been issued across the top and west of the South Island for the coming days.
And parts of the North Island are under a heavy rain watch.
MetService said a deep low over the Tasman Sea would direct “moist northerlies” over the country on Thursday and Friday, bringing heavy rain and strong winds.
“This could be a significant rain event for the Tasman/Nelson districts, and there is a chance that warnings in the area could be upgraded to red,” the forecaster said.
The heaviest rainfall was expected in the Tasman region, northwest of Motueka.
Between 350-450mm of rain were forecast about the ranges, with 150-250mm elsewhere.
Peak rates were expected from late Thursday and there was a “moderate chance” it could be upgraded to a red warning.
Heavy rain was also forecast for the Marlborough District, with 200 to 300mm of rain forecast about the Richmond and Bryant ranges and 100 to 150 mm elsewhere.
Peak rates of 20 to 30 mm/h were expected, mainly about the Richmond and Bryant ranges and there was a “low chance” it will be upgraded to a red warning, MetService said.
The Buller District is expected to be lashed with between 150 to 200mm of rain, potentially up to 250mm around the Paparoa Range.
The ranges of the Westland District were also issued with an orange warning, with 150 to 200mm of rain expected, possibly up to 250mm around isolated peaks.
In the North Island, Mount Taranaki was the sole area issued with an orange heavy rain warning.
MetService said between 150 to 250mm of rain was expected, with peak rates of 15 to 25mm/h.
Streams and rivers could rise rapidly in the above areas, with surface flooding, slips and difficult driving conditions possible, MetService said.
Heavy rain watches were in place for large parts of the country, including Auckland, Northland, Waikato, the Coromandel Peninsula, norther Taranaki, Nelson and Tasman about and southeast of Motueka, as well as the Grey and Westland Districts.
Periods of heavy rain were forecast, with amounts potentially approaching warning criteria. MetService said there was a moderate chance of upgrading these watches to warnings.
There was also a strong wind watch in place for south Taranaki, Taihape and Whanganui.
