Heavy rain and possible severe gales are forecast to strike parts of the lower South Island on Sunday and Monday.
A strong and moist north to northwest flow followed by a slow-moving front is expected to move northwards over these days.
MetService warns this front is forecast to deliver heavy rain and possible severe gales north to northwesterlies to parts of the lower South Island, and watches and warnings are in place.
"On Monday there is high confidence that rainfall accumulations will meet warning criteria in Westland and a severe weather warning is already in force," it warns.
"There is a moderate confidence that rainfall accumulations will meet warning criteria in the headwaters of the Otago and Canterbury Lakes and rivers and severe weather watches are already in force for those areas.
"There is a moderate confidence that rainfall accumulations will reach warning criteria in Buller."
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: 29hrs from 10am Sun, 1 May - 3pm Mon, 2 May
Forecast: Expect 110 to 160mm of rain to accumulate about the ranges, with 70 to 100mm near the coast. Peak rates of 15 to 25mm/h from Sunday afternoon. Rain clearing south of the Glaciers early Monday morning.
Area: Fiordland about and north of Doubtful Sound
Period: 12hrs from 6am - 6pm Sun, 1 May
Forecast: Expect 100 to 130mm of rain. Peak rates of 15 to 25mm/h from late Sunday morning.
Heavy Rain Watch
Area: The headwaters of the Canterbury lakes and rivers, south of Arthur's Pass
Period: 24hrs from 3pm Sun, 1 May - 3pm Mon, 2 May
Forecast: Periods of heavy rain. Rainfall amounts may approach warning criteria within 15km east of the main divide.
Area: The headwaters of the Otago lakes and rivers
Period: 18hrs from 9am Sun, 1 May - 3am Mon, 2 May
Forecast: Periods of heavy rain. Rainfall amounts may approach warning criteria within 15km east of the main divide.
Area: Fiordland south of Doubtful Sound
Period: 9hrs from 6am - 3pm Sun, 1 May
Forecast: Periods of heavy rain. Rainfall amounts may approach warning criteria.
Strong Wind Watch
Area: Canterbury High Country, about and south of Arthur's Pass
Period: 18hrs from 9am Sun, 1 May - 3am Mon, 2 May
Forecast: North to northwest winds may approach severe gale at times.
Area: Fiordland, inland Southland and inland Otago
Period: 21hrs from 3am Sun, 1 May - midnight Sun, 1 May
Forecast: North to northwest winds may approach severe gale at times, especially about higher ground. Winds easing in Fiordland, Southland and Clutha early Sunday afternoon.
