Bay of Plenty is now expected to get up to 90mm of rain from 9am until midnight.
It's feared the intense 15-hour rainfall, including thunderstorms, could lead to further flooding and slips in a region still recovering from last month's devastating cyclone.
The MetService said more heavy rain was expected in the Nelson Ranges from midday and would continue until 7am tomorrow.
Gusts of more than 80km/h were recorded overnight on Auckland's Harbour Bridge as stormy weather whipped Northland and Auckland.
Firefighters cleared trees - and an 8m clown - blown down across roads around Pukekohe.
The worst rainfall hit north of the city, including Warkworth where 51mm fell, and Orewa, which got 36mm.
But despite wild weather, the north continues to enjoy balmy temperatures.
Kaitaia recorded 18C and Auckland maintained a warm 16C.
Temperatures in the north of the country are expected to rise back above 20C during the day while those in the far south are a good 10C cooler ahead of Friday's snow.
MetService forecaster Sarah Sparks said there would be no let-up in the rain until later this afternoon.
"A front is passing over Auckland this morning. We're expecting rain and heavy falls, which is not due to clear until this afternoon."
She said the strong winds should die down this afternoon but showers would return tonight and continue falling tomorrow.
Northern and western regions of both islands remain under a swathe of weather warnings and watches.
Sparks said the entire country was in store for a bleak day with rain forecast everywhere.
The first major cold snap of the year is just 24 hours away as an Antarctic blast comes to coat southern towns and cities in snow.
The MetService is expecting snow to the lowest levels seen this year in Southland, Canterbury, parts of central Otago and Dunedin's hillside suburbs.
Niwa says everywhere can expect temperatures to be like the middle of winter on Friday.
