By Lucy Craymer

Coming top of weeks of damp weather, the latest rainstorms are worsening conditions in New Zealand’s already sodden landscape. Experts have attributed the unseasonably wet weather to a narrow stream of water vapour, or an ‘atmospheric river’, sitting above the country.

Weather forecaster Metservice’s data showed part of the north of the South Island had received well over 300 millimetres of rain (11.8 inches) in the past 24 hours. It has heavy rain warnings in place for parts of the west of the South Island and in the north of the North Island.

Metservice data showed Nelson city on the South Island had received 106 millimetres of rain since midday on Tuesday – well above its average rainfall for the whole of August of 80 millimetres.

On New Zealand’s North Island, the country’s largest city, Auckland, is under a heavy rain and winds alert, with minimal disruption reported so far.

Authorities said more than 230 homes in Nelson, a city with a population of more than 50,000, have already been evacuated with many public facilities and roads are closed.

A statement on Nelson City Council’s website warned continuing rain could mean more land slips, flooding and evacuations.

Nelson’s Mayor Rachel Reese told New Zealand television show AM that while the city had made it through the night without any major incidents, infrastructure was under pressure.

“We are dealing with a lot of wastewater overflows,” she said.

On the west coast of the island Buller District Council said in a statement people from 160 homes evacuated over the last day were able to return to their residences to assess damage. But it warned further rain was expected and it was possible that they would have to evacuate again.

“Right across the district I believe we got away relatively unscathed,” Buller Mayor Jamie Cleine told a news conference streamed online.

(Reporting by Lucy Craymer; Editing by Kenneth Maxwell)