Severe weather watches and warnings have been issued before a front strikes the South Island on Sunday.
Tomorrow, a strong northwest flow followed by an active front with a "significant rain band" will move onto the western and lower South Island, before continuing to sweep northwards on Monday.
"This front is expected to bring periods of heavy rain with thunderstorms and possible downpours to western parts of the South Island," MetService said on its website.
"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. A watch for strong northwesterlies is also in place for 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."
Heavy Rain Warning - Orange
Impact: Heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous.
Area: Westland south of Otira
Period: 12hrs from 5pm Sun, 12 Mar - 5am Mon, 13 Mar
Forecast: Expect 70 to 110mm of rain about the ranges, with lesser amounts nearer the coast. Peak rates of 15 to 25mm/h, but 25 to 40mm/h south of Mt Cook in thunderstorms and possible downpours.
Period: 12hrs from noon Sun, 12 Mar - midnight Sun, 12 Mar
Forecast: Expect 100 to 140mm of rain. Peak rates of 25 to 40mm/h in thunderstorms and possible downpours.
Heavy Rain Watch
Area: For headwaters of the Otago and Canterbury lakes and rivers south of Mt Cook
Period: 7hrs from 9pm Sun, 12 Mar - 4am Mon, 13 Mar
Forecast: Periods of heavy rain. Rainfall amounts may approach short duration warning criteria.
Area: Southland and Clutha
Period: 10hrs from 5pm Sun, 12 Mar - 3am Mon, 13 Mar
Forecast: Periods of heavy rain. Rainfall amounts may approach warning criteria.
Strong Wind Watch
Area: Canterbury High Country
Period: 8hrs from 10pm Sun, 12 Mar - 6am Mon, 13 Mar
Forecast: Northwest winds may approach severe gale at times