MetService has issued a Severe Weather Watch for the Bay of Plenty and Coromandel Peninsula regions.

Heavy rain is expected overnight for both the Coromandel Peninsula and western Bay of Plenty.

A low pressure system is forecast to approach and move over northern New Zealand from the northwest during the weekend, while slowly weakening.

An associated front is expected to bring a period of heavy rain to northern regions.

The Heavy Rain Watch for Coromandel Peninsula is valid for 15 hours from 1am to 4pm, Sunday, November 19.

"A period of heavy rain, with thunderstorms possible," says a MetService spokesperson. 

"Rainfall amounts may approach warning criteria, especially about the ranges."

A Heavy Rain Watch also issued for the Bay of Plenty area west of Whakatane is valid for 18 hours from 2am - 8pm on Sunday, November 19.

"A period of heavy rain. Rainfall amounts may approach warning criteria, especially about higher ground."

People are advised to keep up to date with forecasts as changes could be made.

Monday and Tuesday forecast

A low is expected to lie slow moving north of Bay of Plenty during Monday and Tuesday while weakening.

"There is moderate confidence that heavy rain in Gisborne/Tairawhiti, Hawke's Bay and eastern Taihape will require a warning on Monday and Tuesday," says a MetService weather forecaster.

"The confidence that a warning will be required for Wairarapa during this time is low. There is also low confidence that a heavy rain warning will be required for Mount Taranaki during Monday."

A couple of fronts are likely to affect the South Island on Wednesday and Thursday.

"These may bring brief heavy rain to Fiordland and Westland, and strong west to northwest winds to exposed parts of Southland and Otago. However, currently confidence is very low that warnings will be required for heavy rain or strong winds."