A broad trough over the country shifts north over the North Island on Thursday, says MetService which has issued a severe weather watch on Sunday.

Strengthening moist easterly winds are also expected to affect the east of the South Island on Thursday.

"A ridge is expected to build to the east of the South Island late Friday and early Saturday, then extends onto the North Island late Saturday. Northeasterlies then become strong in the north of the North Island on Saturday," says a MetService spokesperson.

There is moderate confidence that rainfall amounts may reach warning criteria from the Kahurangi National Park to southern Westland on Wednesday, especially about the ranges.

During Thursday and Friday, there is low confidence that warning amounts of rain will fall in eastern parts of the South Island from South Canterbury to Clutha, as indicated on the chart.

MetService Severe Weather Watch
Heavy rain and strong winds are forecast for parts of central and southern New Zealand this week.

"A large, complex trough continues to bring unsettled weather to the country, with an embedded low approaching the west coast of the South Island," says a MetService spokesperson.

Warnings and Watches are in place for Heavy Rain and Strong Winds for parts of central and southern New Zealand.

People are advised to keep up to date with the latest forecasts in case changes are made, or further areas are added.

Heavy Rain Watch
Area: Tararua Range
Valid: 40 hours from 2:00pm Mon 10 Apr to 6:00am Wed 12 Apr
Forecast: Periods of heavy rain. Rainfall amounts may approach warning criteria. Thunderstorms possible.
Note: Validity extended to 6am Wednesday.

Area: Buller
Valid: 38 hours from 9:00am Mon 10 Apr to 11:00pm Tue 11 Apr
Forecast: Periods of heavy rain. Rainfall amounts may approach warning criteria, especially south of Seddonville. Heaviest rain is likely during Tuesday, and this Watch may be upgraded to a Warning.

Note: The validity may be extended into Wednesday.

Strong Wind Watch
Area: Buller from around Seddonville southwards, and Westland from Harihari northwards
Valid: 8 hours from 4:00am Tue 11 Apr to 12:00pm Tue 11 Apr
Forecast: Northerly winds may approach severe gale at times.

Watches no longer in Force
Heavy Rain Watch lifted for Bay of Plenty ranges east of Opotiki: Heavy rain has eased.

MetService Severe Weather Warning
Heavy rain and strong winds are forecast for parts of central and southern New Zealand

A large, complex trough continues to bring unsettled weather to the country, with an embedded low approaching the west coast of the South Island.

Warnings and Watches are in place for Heavy Rain and Strong Winds for parts of central and southern New Zealand.

People are advised to keep up to date with the latest forecasts in case changes are made, or further areas are added.

Heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous.

Area: Mount Taranaki
Valid: 6 hours from 9:00am Mon 10 Apr to 3:00pm Mon 10 Apr
Forecast: Another 40 to 60 mm on top of what has already fallen. Thunderstorms possible with rainfall rates of 15 to 25 mm/h, and maybe more.

Area: The Richmond and Bryant Ranges, including the Rai Valley
Valid: 9 hours from 9:00am Mon 10 Apr to 6:00pm Mon 10 Apr
Forecast: Another 40 to 60 mm of rain expected on top of what has already fallen. Peak rates of 15 to 25 mm/h in possible thunderstorms.
Note: a few heavy showers expected Monday evening.

Area: Tasman District northwest of Motueka
Valid: 9 hours from 9:00am Mon 10 Apr to 6:00pm Mon 10 Apr
Forecast: Expect another 40 to 50 mm on top of what has already fallen, mainly about the ranges. Peak rates of 15 to 25 mm/h in possible thunderstorms.
Note: a few heavy showers expected Monday evening.

Area: Westland
Valid: 38 hours from 9:00am Mon 10 Apr to 11:00pm Tue 11 Apr
Forecast: Expect periods of heavy rain today which do not meet warning criteria. However, during Tuesday expect 140 to 200 mm about the ranges, and 60 to 100 mm near the coast, especially north of the Glaciers.
Note: the validity is likely to be extended into Wednesday.