"The western and alpine areas of the South Island may see another period of heavy rain, which may pose problems to those areas affected by the wet weather of last week," he said.
About 300mm of heavy rain is expected to fall in the same catchment areas of the Southern Alps that were drenched last week.
The deluge has prompted Environment Canterbury to issue flood warnings, while the New Zealand Transport Agency (NZTA) has closed part of State Highway 94/Milford Rd as a precaution against rock fall.
Campers, farmers and other landowners in the area have been told to monitor the situation closely as rivers could still become unsafe from floodwaters flowing rapidly downstream.
NZTA Southland state highway operations manager Peter Robinson said the Milford Rd was closed between the Homer Tunnel and Murrell's Bridge from 7pm today due to the heavy rain forecast in the area.
Heavy rain in Westland, Nelson and Buller last week washed away a bridge and caused holiday traffic mayhem.
The wild weather washed out a section of Wanganui River bridge at Harihari, south of Hokitika, on Wednesday, forcing holidaymakers to make lengthy detours.