Heavy rain is being forecast for Fiordland, Westland and the headwaters of Otago Lakes and Rivers.
Severe gales for parts of the South Island are also being predicted for the area, with the MetService issuing a severe weather watch for the region.
"An active front, preceded by a strong and very moist northwest, is expected to move northeast across the South Island on Saturday, followed by very strong and showery west to southwesterly flow.
"The front should move over the North Island on Sunday and weaken.
"The heaviest falls are expected in Fiordland and Westland south of Otira, also about the headwaters of the Otago Lakes and Rivers, where a heavy rain warning is now in force."
In addition, the strongest winds are expected about the Canterbury High Country ahead the front, and about coastal Southland and southern parts of Otago behind the front, where a Strong Wind Warning is in force.
People are advised to keep up to date with the latest forecasts in case further areas are added to this Warning.
HEAVY RAIN WARNING
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
Valid: 12 hours from 10am to 10pm Saturday
Forecast: Expect 100 to 160mm of rain to accumulate about the ranges, and 60 to 100mm near the coast. Peak intensities 25 to 35mm per hour about the ranges.Thunderstorms possible.
Valid: 14 hours from 6am to 8pm Saturday
Forecast: Expect 120 to 180mm of rain to accumulate, especially north of Doubtful Sound. Peak intensities 20 to 30mm per hour, and thunderstorms possible.
Change note: Upgraded to a full warning.
Area: The headwaters of the Otago Lakes and Rivers
Valid: 12 hours from 8am to 8pm Saturday
Forecast: Expect 100 to 160mm of rain to accumulate near the main divide, and 70 to 100mm within 15km east of the divide. Peak intensities 15 to 25mm per hour.Thunderstorms possible.
STRONG WIND WARNING
Strong wind gusts could damage trees, powerlines and unsecured structures.Driving may be hazardous, especially for high-sided vehicles and motorcycles.
Area: Canterbury High Country
Valid: 9 hours from 1pm to 10pm Saturday
Forecast: Northwest gales are forecast to be severe at times, with gusts reaching 130 km/h or more in exposed parts.
Area: Coastal Southland and Clutha, also eastern part of Dunedin
Valid: 13 hours from 8pm Saturday to 9am Sunday
Forecast: West to southwest gales are forecast to be severe in exposed parts at times, with gusts reaching 120 to 130km/h.