A moist northerly air stream is bringing heavy rain to northern and western parts of the South Island through to Tuesday, says MetService.

Heavy rain is also forecast to affect northern and western parts of the North Island from Tuesday.

MetService has issued a Heavy Rain Watch on Sunday morning. People are advised to keep up to date with the latest forecasts.

Area: Northland

Valid: 15 hours from 3:00am Tue 9 May to 6:00pm Tue 9 May
Forecast: Periods of heavy rain, with thunderstorms possible. Rainfall amounts may approach warning criteria and this watch is likely to be upgraded to a warning closer to the time.

Area: Auckland including Great Barrier Island, and Coromandel Peninsula
Valid: 14 hours from 10:00am Tue 9 May to 12:00am Wed 10 May
Forecast: Periods of heavy rain. Rainfall amounts may approach warning criteria.

Area: North Taranaki
Valid: 15 hours from 9:00am Tue 9 May to 12:00am Wed 10 May
Forecast: Periods of heavy rain. Rainfall amounts may approach warning criteria.

Area: Marlborough about and north of the Awatere Valley, also Nelson and Tasman south and east of Motueka
Valid: 15 hours from 6:00am Tue 9 May to 9:00pm Tue 9 May
Forecast: Periods of heavy rain. Rainfall amounts may approach warning criteria.

Area: Buller
Valid: 12 hours from 9:00am Sun 7 May to 9:00pm Sun 7 May
Forecast: Periods of heavy rain. Rainfall amounts may approach warning criteria.
Note, another period of significant rain is expected from late Monday or Tuesday, and this Watch maybe extended or upgraded to a warning closer to the time.

Area: Canterbury headwaters south of Arthurs Pass
Valid: 5 hours from 9:00am Sun 7 May to 2:00pm Sun 7 May
Forecast: Periods of heavy rain. Rainfall amounts may approach warning criteria within 20 km of the main divide.

Area: Otago headwaters
Valid: 21 hours from 6:00pm Mon 8 May to 3:00pm Tue 9 May
Forecast: Periods of heavy rain. Rainfall amounts may approach warning criteria within 20km.

A Severe Weather Warning has been issued by MetService for the following regions:

Area: Tasman from Motueka westwards
Valid: 12 hours from 9:00am Sun 7 May to 9:00pm Sun 7 May
Forecast: Expect a further 60 to 90 mm about the ranges and 30 to 50 mm near the coast. This is in addition to what has already fallen. Peak rates of 15 to 25 mm/h.
Note, another significant period of rain expected from late Monday or Tuesday and this warning may be extended.

Area: Westland
Valid: 54 hours from 9:00am Sun 7 May to 3:00pm Tue 9 May
Forecast: Expect 350 to 450 mm of rain about the ranges, and 150 to 200 mm nearer the coast mainly south of Otira. Peak rates of 20 to 30 mm/h, especially about the ranges.
Note, heavy rain spreading south this morning and afternoon.

Area: Fiordland north of Doubtful Sound
Valid: 27 hours from 12:00pm Mon 8 May to 3:00pm Tue 9 May
Forecast: Expect 120 to 180 mm of rain, with higher accumulations expected in the north. Peak rates of 20 to 30 mm/h from Monday evening until Tuesday morning.

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