High winds and heavy rain are forecast for much of Otago, Southland, Westland and Canterbury.
MetService says prolonged heavy rain is forecast on Monday for Fiordland and Westland, which is expected to swell rivers and streams in Otago and Canterbury.
Rain is expected to continue until Wednesday with between 500- 600mm in the Westland ranges.
Severe gales are also forecast for parts of inland Otago and Canterbury from Monday afternoon, reaching gale force in exposed areas.
Wind gusts could reach up to 140km per hour from Tuesday.