A Canterbury Regional Council spokesperson said heavy rain on the West Coast overnight would mean higher than normal flows in rivers popular for recreational activities.
The Waiau Uwha, Hurunui, Rakaia, Rangitata and Waimakariri rivers may all be affected. Anyone on those rivers is asked to be prepared for a rapid rise in water flows.
The council said staff would continue to monitor the rivers, and update alerts for any flooding across the weekend.
On Sunday, another front moves onto the North Island from the west, bringing rain to many parts of the island, with heavy rain watches in force for Waitomo, Taumarunui, Taupō, and Tongariro National Park.
Finally, another front moves onto the southern half of the South Island on Sunday from the west, with heavy rain watches in force for Fiordland and the south of the Westland District.
Heavy rain that fell overnight and this morning is being described as a short, sharp dousing.
Up to 200 millimetres of rain affected Haast through to Hokitika as a wet front sweeps up the motu.
The chair of the West Coast Regional Council, Peter Haddock, said the region has emerged relatively unscathed, and the Waiho River has stayed at regular flows.
State Highway 6 between Fox Glacier and Franz Josef has re-opened after being closed due to a tree blocking the road.
Waka Kotahi said the road closed at 8.30am today.