Uninterrupted downpours lasting more than 24 hours could cause havoc in eastern parts of the North Island, with forecasters warning of potential floods and slips.
NIWA Weather also anticipates "extremely high" river flows to develop in Gisborne and northern Hawke's Bay by Thursday morning.
They are cautioning locals not to attempt to cross any floodwaters and to follow the advice of emergency officials.
It comes amid extreme rainfall totals for parts of the east coast, with around 70mm of rain falling in Gisborne so far and more to come.
"Some areas will see two-three times their normal November monthly rainfall in just two days," NIWA said in a tweet on Wednesday. "This will result in a rapid rise in rivers/streams, as well as flooding and slips."
WeatherWatch says the torrential rain is caused by a "weak low to the north, with sub-tropical connections plus a powerful high to the south" and will last well into Thursday along with lower temperatures.
"Our estimates show over 150mm is possible lower down and maybe over 200mm higher up," the forecaster says.
Earlier, MetService issued a heavy rain warning for Gisborne with 150-220mm and Hawke's Bay north of Napier may receive 140mm.
Elsewhere, strong wind watches and warnings were put in place for other parts of the North Island. Tokoroa copped some of the worst of the gales, with trees falling and some damage to property.
The South Island, in stark contrast, will largely get a very settled few days - particularly on the traditionally very wet West Coast. Greymouth looks set to enjoy five rain-free days in succession.
