Southern Westland and Fiordland can expect a heavy dump of rain towards the end of the week and it could spill over into Canterbury and Otago's lakes and rivers, forecasters say.
Rain pouring off a roof.
An active front is forecast to move onto the South Island from the west during today and tomorrow, the MetService says.
The Westland ranges south of Otira could get up to 220mm of rain over a nine-hour period from 6pm this evening, prompting a warning about rapidly rising waterways and surface flooding and slips.
The heavy rain was also forecast to spill over into the headwaters of Canterbury and Otago lakes and rivers during this time.
The Southern Alps, south of Arthur's Pass, could expect up to 190mm of rain in a 17-hour period from 11pm tonight.