"It is a really slow-moving front and a lot of rainfall associated with it, there is some places that could see 30 to 45 mm heavy rain in an hour," Murray said.
Surface flooding had already been reported by NZTA on State Highway 60 Takaka to Collingwood.
Flooding near the Little Onahau River Bridge had caused a temporary speed limit to be put in place. Road users were advised to take extra care.
Shady Rest owner Mark Taylor said he had left Takaka to go to Motueka and the rain had been very heavy but the roads were still in good condition.
"It's really bad. It is a heavy downpour."
Murray said the front was "really slow" moving and would stick around for some time.
"The front is coming from Northland coming down Farewell Spit, and wrapping around the Cook Strait and then coming to the east of the Banks Peninsula."
On the West Coast of the South Island Franz Josef had already recorded 50mm in the last 12 hours, with Hokitika (31mm) and Milford had 44mm also experiencing a downpour.
A wet-weather warning was in place for Auckland from 6am Thursday to 6am Friday, with a potential for 80mm to 120mm to fall.
Murray advised everyone to keep an eye of Metservice reports to be best prepared.
The wet weather did not mean cooler temperatures and many Kiwis could find it hard to sleep with the high humidity, she said.
"Overnight it is quite warm still; the warm overnight temperatures will stick around.
"It's a warm air mass, we are not going to see temperatures in the 30s but it will be quite muggy," Murray said.
