MetService warns heavy rain, "damaging winds" and thunderstorms may rattle the upper North Island on Sunday afternoon.
The active front could cause winds up to 110km/h, small tornadoes and "severe thunderstorms", the forecaster says.
"This thunderstorm activity is expected to affect Northland in the late afternoon or early evening. Auckland, the Hauraki Gulf and Coromandel Peninsula in the early evening," MetService said in its Thunderstorm Outlook.
"Then Bay of Plenty and possibly Waikato to Taranaki this evening or tonight."
The thunderstorms may continue until Monday night. A heavy rain watch warning is in place for areas in Northland, Auckland, The Coromandel, Taranaki, Bay of Plenty, Great Barrier Island and Nelson.
MetService says the forecast is a "far cry" from Sunday morning's calm conditions.
"After a relatively quiet Sunday morning, conditions will worsen in the upper North Island during the afternoon and evening," weather research agency NIWA weather tweeted on Saturday morning.
MetService said its rain radar was kept busy by the active front overnight, but will receive a short break before the next round of rainy weather expected Sunday afternoon.
