The MetService has issued an Orange heavy rain warning for the headwaters of Lake Wānaka and Lake Hāwea from 4pm Sunday (May 25) to 2am Monday (May 26).

A front sweeps over the South Island from the Tasman Sea during Sunday and Monday, bringing a period of heavy rain and strong north to northwest winds.

Expect 80 to 100 mm of rain near the main divide and 70 to 90 mm within 15km east of the divide. Peak rates of 15 to 25 mm/h expected about the divide with possible thunderstorms.

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

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