Photo: Unsplash / Erik Witsoe
Auckland and parts of Northland might experience a deluge over a period of 29 hours while parts of Coromandel will also come in for a soaking.
MetService has put three heavy rain watches in place.
Auckland, south of the Bay of Islands and north of Orewa, will be affected by periods of heavy rain from 10pm today through until 3am on Tuesday.
A band of rain is expected to move slowly southwards, bringing possibly heavy rainfall, MetService said.
"There is a risk that the rain-band could become stationary at times, increasing rainfall accumulation in localised places, where amounts may approach warning criteria especially in the east," it said.
Northland might also experience thunderstorms on Monday morning.
The region's heavy rain watch is due to be lifted at 3am on Monday. Over the next few hours, an area about and north of the Bay of Islands could be in for spells of heavy rain.
A heavy rain watch is also in place for Great Barrier Island, the Hunua Range and Coromandel Peninsula from 1am to 6pm on Tuesday.
MetService said there was some uncertainty about the forecasts, and it warned people to stay up to date in case changes were made.
It said a large trough would lie over the country on Tuesday and Wednesday bringing unsettled conditions.
Severe gales may affect Wellington, Wairarapa, Marlborough and Canterbury on Wednesday and early Thursday.