MetService has issued a Severe Weather Warning due to heavy rain and northerly gales impacting western and northern parts of New Zealand this weekend.

"A front is forecast to move across the South Island from the west today and across the North Island on Sunday," says a MetService spokesperson.

"The front is expected to bring a period of heavy rain and northerly gales to parts of the country, with Warnings and Watches for Heavy Rain and Strong Winds in force."

People are advised to keep up to date with the latest forecasts in case any changes are made.

A Heavy Rain Warning has been issued for the following regions:

Area: Bay of Plenty east of Kawerau and Tairawhiti/Gisborne north of Ruatoria
Valid: 21 hours from 12am - 9pm Sunday August 20
Forecast: Expect 100 to 140 mm of rain, where highest accumulations are expected about the ranges. Peak rates of 15 to 25 mm/h expected during Sunday morning and afternoon.

Area: Mount Taranaki
Valid: 19 hours from 2pm Satuday August 19 to 9am Sunday August 20
Forecast: Periods of heavy northerly rain. Expect 100 to 140 mm, with peak intensities of 15 to 20 mm/h from Saturday night to Sunday morning.

Area: Tasman, about and west of Motueka
Valid: 14 hours from 10:00am Sat 19 Aug to 12:00am Sun 20 Aug
Forecast: A period of heavy northerly rain. Expect 70 to 90 mm of rain, with peak intensities of 15 to 25 mm/h during late afternoon and evening.

Area: The ranges of Westland south of Otira
Valid: 12 hours from 12:00pm Sat 19 Aug to 12:00am Sun 20 Aug
Forecast: Periods of heavy northerly rain. Expect 70 to 100 mm, with peak intensities of 15 to 20 mm/h and possible thunderstorms Saturday afternoon and evening. Note, further rain is possible through to Sunday morning and this Warning could be extended.

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

Strong Wind Warning
A Strong Wind Warning has been issued for Fiordland about the fiords. This warning is valid for seven hours from 9am - 4pm Saturday August 19. Northeast gales gusting 130 km/h are forecase for exposed places, especially about the coast.

Strong wind gusts could damage trees, powerlines and unsecured structures. Driving may be hazardous, especially for high-sided vehicles and motorcycles.

Heavy Rain Watch
Area: Northland and Auckland including Great Barrier Island
Valid: 12 hours from 12:00am Sun 20 Aug to 12:00pm Sun 20 Aug
Forecast: Periods of heavy rain, and amounts may approach warning criteria in localised areas.

Area: Waikato, Coromandel Peninsula, Taupo, and Bay of Plenty about and west of Kawerau including Rotorua
Valid: 12 hours from 4:00am Sun 20 Aug to 4:00pm Sun 20 Aug
Forecast: Periods of heavy rain, and amounts may approach warning criteria in localised areas.

Area: Central North Island hill country from eastern Taranaki to Taihape, and northwards to Waitomo
Valid: 16 hours from 8:00pm Sat 19 Aug to 12:00pm Sun 20 Aug
Forecast: A period of heavy northerly rain, and accumulations may approach warning criteria.

Area: Bryant and Richmond ranges including the Rai Valley
Valid: 12 hours from 2:00pm Sat 19 Aug to 2:00am Sun 20 Aug
Forecast: Periods of heavy rain, and amounts may approach warning criteria.

Area: Buller
Valid: 13 hours from 11:00am Sat 19 Aug to 12:00am Sun 20 Aug
Forecast: A period of heavy northerly rain with possible thunderstorms, and accumulations may approach warning criteria

Area: Fiordland north of Doubtful Sounds
Valid: 21 hours from 12:00pm Sat 19 Aug to 9:00am Sun 20 Aug
Forecast: Periods of heavy rain, and amounts may approach warning criteria.

Strong Wind Watch
Area: South Taranaki, Taihape, and Whanganui north of the City
Valid: 14 hours from 11:00am Sat 19 Aug to 1:00am Sun 20 Aug
Forecast: Northerly winds may approach severe gale in exposed places.

Area: Tasman and Nelson
Valid: 6 hours from 2:00pm Sat 19 Aug to 8:00pm Sat 19 Aug
Forecast: Northerly winds may approach severe gale in exposed places.

Area: Westland and Buller
Valid: 7 hours from 9:00am Sat 19 Aug to 4:00pm Sat 19 Aug
Forecast: Northeast winds may approach severe gale, especially about the coast.

Area: Canterbury High Country
Valid: 10 hours from 6:00pm Sat 19 Aug to 4:00am Sun 20 Aug
Forecast: Northwest winds may approach severe gale in exposed places.