MetService has issued a severe weather warning for parts of the North Island.

"Heavy rain [is] possible for parts of the upper North Island," says a MetService spokesperson.

"Slow-moving fronts affect the North Island tonight and Wednesday, possibly bringing heavy rain to parts of the upper North Island."

People are advised to keep up to date with the latest forecasts in case any changes are made.

A heavy rain watch has been issued for Great Barrier Island and Northland south of Kawakawa. This is valid for 18 hours from 5am to 11pm on Wednesday. Periods of heavy rain and possible thunderstorms are forecast and rainfall amounts may approach warning criteria.