The MetService has issued an Orange heavy rain warning for the headwaters of Lake Wānaka and Lake Hāwea for tomorrow (December 8) from 6am to 3pm.

An intense front embedded in a strong and moist northwesterly flow moves north over the South Island on Sunday bringing heavy rain, mainly to the west of the South Island.

Expect 120 to 150 mm of rain near the main divide and 80 to 100 mm within 20 km east of the divide. Peak rates of 15 to 25 mm/h expected about the divide with possible thunderstorms after 9am.

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.