A heavy rain watch is in place for the Bay of Plenty region, including Rotorua, and Taupo, says a MetService spokesperson.

Periods of heavy rain with possible downpours and thunderstorms are forecast, from 8am to 11pm, today, Saturday April 20.

"Amounts may approach warning criteria and may even exceed warning amounts in localised areas," says a MetService spokesperson.

A heavy rain watch is also in place for Northland, Auckland, Coromandel Peninsula, Waikato, Waitomo, which is valid for 16 hours from 4am to 8pm today, Saturday April 20.

Periods of heavy rain with possible downpours and thunderstorms are forecast for these regions and amounts may also approach and even exceed warning amounts in localised areas.

Rain with possible downpours is forecast for the north of the North Island on Saturday.

"A low pressure system is forecast to move eastwards across northern New Zealand during Saturday.

"The low is expected to be accompanied with bands of rain, which are likely to be heavy in areas of the north of the North Island."

MetService says there is uncertainty with how widespread the heavy rain will be.

"However, there is the likelihood that there will be localised downpours and thunderstorms as well, and that amounts could approach and may even exceed warning amounts in localised areas."

People are advised to keep up to date with the latest forecasts.