Flooding possible for parts of South Island later this week

Heavy rain forecast for much of New Zealand this week could cause flooding in parts of the South Island.

People in the upper South Island may need to get their umbrellas out from Tuesday night to Thursday morning.

Forecaster WeatherWatch.co.nz is warning inland parts of  both islands - Bay of Plenty, South Waikato, Taranaki and Nelson - could get a month of rain in just seven days.

Flooding is also possible for both islands, according to the weather service.

The heavy rain is due to a low forming across the Tasman Sea and is forecast to hit NZ on Tuesday, Wednesday and Thursday as it crosses the country, WeatherWatch said.

The places sheltered from the heavy dumps include Northland, Gisborne, Southland, Otago and southern parts of Canterbury.

However, the rain may not arrive in the region arguably most in need of it, with Auckland - which has had water restrictions in place since May - right on the cusp of the heavier falls.

Auckland could instead be in for heavy wind and even gales from the north and west, which could result in some power cuts from falling trees.