The MetService has issued an Orange heavy rain warning for the headwaters of Lake Wānaka and Lake Hāwea from 1am-10am Saturday (October 18).

A frontal rain band, preceded by strong-to-gale northwesterlies, moves north over the South Island between late Friday and early Sunday.

Expect 90 to 120 mm of rain near the main divide and 60 to 90 mm within 20km east of the divide. Peak rates of 20 to 30 mm/h expected about the divide.

Heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous.

Strong winds may damage trees, powerlines, and unsecured structures. Driving may be difficult, especially for high-sided vehicles and motorcycles.

Anyone heading into Mt Aspiring National Park is advised to take extra care or delay travel.