The MetService has issued an Orange heavy rain warning for the headwaters of Lake Wānaka and Lake Hāwea from 3am-4pm Wednesday September 17.

A front is preceded by a humid northwest flow, bringing heavy rain and strong winds to the region.

Expect 150 to 200 mm of rain near the main divide and 80 to 140 mm within 20km east of the divide. Peak rates of 25 to 35 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.

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