Heavy rain forecast for South Island mid-next week

Heavy rain is forecast for the western parts of the South Island in the middle of next week, MetService says.

"We have this system over the east coast of Australia that is moving towards New Zealand," said MetService meteorologist Alec Holden.

He said forecasts showed it would impact "the West Coast of the South Island most, such as Westland", however north and south of the area could also be affected.

MetService said there was a high confidence of rain for central and southern parts of Westland to reach warning levels.

There was a moderate confidence for rain to reach warning levels in northern Fiordland, including spillover into the headwaters of Otago and Canterbury lakes and rivers.

As for rain in other areas of Fiordland, south of Bligh Sound and also in Grey and Buller, there was a low confidence of reaching severe weather levels, it said.

Those in exposed inland parts of the South Island from north Canterbury to central Otago could also experience severe north to northwest gales, with a low confidence of the wind reaching warning levels, said the MetService.

Niwa has also warned that the odds for a "significant rain event" was growing as an atmospheric river teams up with low pressure.

The risk of flooding was a concern, it said.