Southerners are being urged to keep an eye on the skies over the next two days.
A MetService spokesman said an active front, preceded by a strong northwest flow, was forecast to move north over the South Island during Sunday and early Monday.
"This front is expected to bring periods of heavy rain with thunderstorms and possible downpours to western parts of the South Island.
"Heavy rain warnings are in force for Fiordland and Westland, while rain watches are in place for Southland, Clutha and for the headwaters of the Otago and Canterbury lakes and rivers.
"Heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous."
In Fiordland, between midday Sunday and early Monday morning, up to 140mm of rain was expected to fall, with peak rates of up to 40mm per hour.
He said a watch was also in place for strong northwesterlies in the Canterbury High Country.
"People in these areas are advised to stay up to date with the latest forecasts in case any changes are made, or more areas are added."
