Heavy rain is forecast for eastern parts of the South Island today, and eastern Bay of Plenty on Sunday.

A large, slow-moving low pressure system over the Tasman Sea sea will continue to bring showers to most of the country over the weekend, with thunderstorms also possible in many regions, says a MetService spokesperson.

"A rain-band associated with the low moves slowly southwards over Canterbury and Otago today, bringing easterly rain there.

A slow-moving trough is then expected to bring a burst of northerly rain to eastern Bay of Plenty tomorrow.

People are advised to keep up to date with forecasts.

Heavy Rain Warning for Canterbury and North Otago:
Heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous.

Area: Canterbury
Valid: 12 hours from 9:00am Sat 19 Nov to 9:00pm Sat 19 Nov
Forecast: Expect 60 to 90 mm of rain to accumulate about eastern parts of the High Country and foothills south of the Rangitata River, and 20 to 60 mm elsewhere. These amounts are in addition to the rain that has already fallen today. Peak rates of 10 to 15 mm/h. Note, the rain should ease in the north this afternoon.

Area: North Otago
Valid: 12 hours from 11:00am Sat 19 Nov to 11:00pm Sat 19 Nov
Forecast: Expect 40 to 70 mm of rain to accumulate. Peak rates around 10 mm/h.

Heavy Rain Watch for eastern Bay of Plenty and Dunedin:

Area: Bay of Plenty east of Whakatane
Valid: 12 hours from 12:00am Sun 20 Nov to 12:00pm Sun 20 Nov
Forecast: A period of heavy rain, with thunderstorms possible. Amounts may approach warning criteria.

Area: Dunedin
Valid: 12 hours from 1:00pm Sat 19 Nov to 1:00am Sun 20 Nov
Forecast: A period of rain, which could be heavy at times. Rainfall amounts may approach warning criteria near the coast.

Watches no longer in Force
Heavy Rain Watch lifted for The Kaikoura Coast and Ranges: Heavy rain has eased so the watch is lifted. However, scattered heavy showers and thunderstorms are possible this afternoon and evening.

Weather forecast for regions around New Zealand from WeatherWatch:

Northland, Auckland, Waikato and Bay of Plenty
Showers, heavy with thunderstorms especially in the afternoon then easing overnight. North to northwesterly winds.
Highs: 20-23

Western North Island (including Central North Island)
Occasional showers, some may become heavy with thunder especially afternoon then easing at night. North to northwesterly winds.
Highs: 18-24

Eastern North Island
Any early morning rain clears then sun increases, isolated showers develop about Wairarapa in the afternoon possibly heavy with thunder. Northerlies.
Highs: 24-26

Wellington
Any early rain eases to occasional showers, northerly winds.
Highs: 19-23

Marlborough & Nelson
Cloudy areas and showers, chance of an isolated heavy fall and perhaps some thunder in the afternoon for inland hills and ranges then easing at night. Nelson and the Sounds may have slightly more persistent rain during the day. Northerly winds.
Highs: 19-21

Canterbury
Rain in the morning with heavy falls possible then easing to showers as a front pushes to the south, rain may not ease about South Canterbury till evening. Showers become heavy in the afternoon about inland North Canterbury, perhaps a thunderstorm. Easterlies ease, especially later in the day.
Highs: 16-21

West Coast
Patchy rain or showers, Fiordland is dry in the morning then showers develop during the afternoon. Becoming unstable for Buller in the afternoon with a chance of thunderstorms then easing later in the day. Light winds.
Highs: 19-22

Southland & Otago
Mostly cloudy for Southland, Otago has patchy rain with heavier rain about the coast from midday then easing at night. Easterly winds, fresh about the coast.
Highs: 15-20