The Wellington Region Emergency Management Office is on alert, saying there is potential for surface water in Porirua, Hutt and Kapiti. It could affect travel across the region, the office said.
"As the ground is already sodden from last week's rain, there could be some issues - there is the potential for surface water in Porirua, Hutt and Kapiti. It could be a slow commute, so be prepared," the authority posted on its Facebook page.
A major slip already blocking the Ngaio Gorge is not expected to be cleared for up to a fortnight.
Homes were evacuated last week in downtown Wellington after hillsides started to collapse, leaving two properties in peril.
In the past month, slips have blocked a number of other key routes across the region including the Ngauranga Gorge and the Paekakariki Hill Rd.
MetService says 70 to 100mm of rain is expected to fall in the Tararua Ranges throughout the day.
The wet weather stretches up the western side of the North Island. Kapiti Coast, Horowhenua and southern parts of Manawatu can expect problems from flooding and slips.
MetService has also put out a watch for heavy rain on the upper slopes of Mt Taranaki from midday today.
It warned the deluge was likely to lead to snowmelt causing additional run-off into swollen rivers and streams.
Trampers intending to go into southern North Island mountains are being warned to look out for rapidly rising waterways.
