An active front is forecast to move north over the South Island today and early Monday.
"This front is expected to bring a brief period of heavy rain, with thunderstorms and downpours possible about 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 the headwaters of the Otago and Canterbury lakes, Buller and Tararua Range.
The forecaster's 12-hour heavy rain watch for Clutha and Southland starts at 4pm today, with periods of heavy rain, "and amounts may approach warning criteria."
A similar warning have been issued for the headwaters of the Otago and Canterbury lakes and rivers south of Mt Cook from 9pm tonight.
Periods of heavy rain are forecast in amounts that "may approach short duration warning criteria" within 15km from the main divide.
A watch for severe northwest gales is in place for the Canterbury High Country, Marlborough, Wellington and Wairarapa.
