Warning amounts of rain are expected to fall in Fiordland and the headwaters of Otago lakes and rivers over the next few days.
A MetService spokesman said a complex low pressure system arrived from the west yesterday, bringing periods of heavy rain overnight, approaching warning criteria.
He said the weather system was forecast to move slowly over the South Island from today until Saturday, bringing an "extended period of significant heavy rain'' to many places in the South.
"The heaviest rain is expected in Westland, Fiordland and the headwaters of Canterbury and Otago lakes and rivers, and there is high confidence of rainfall accumulations reaching 'warning' criteria in these areas on Wednesday and Thursday.''
He said the risk reduced to low on Friday and Saturday.
A heavy rain warning was already in force for Westland (south of Otira), the Canterbury high country south of Arthurs Pass, and Fiordland.
"Total rainfall accumulations in Westland are expected to be large, possibly 400mm to 600mm during this event, and may cause disruptions.
There was a risk of flooding.
"Also, there is low confidence of warning amounts of rain in North Otago, Dunedin, Clutha and Southland on Friday and Saturday.
"People are advised to
keep up to date with the latest forecasts in case any upgrades are made, or further areas are added,'' he said.
The West Coast Civil Defence Emergency Management Group said it was a busy time in the area for recreational activities around waterways and coastal areas.
Regional director Mark Crowe said large numbers of whitebaiters were out fishing and, combined with the second week of the school holidays, more people than usual were likely to be in areas at risk of flooding.
