Civil Defence is working with coastal scientists as a storm surge is predicted for the already-soaked Coromandel peninsula.
It comes as a section of highway that connects the Coromandel township with Whitianga has been blocked by a slip.
State Highway 25 is closed between Coromandel township and Te Rerenga.
Waka Kotahi said there is no detour for motorists to use and advised holidaymakers and locals to delay their journey.
The road closed just before 11:30pm on Friday.
Thames-Coromandel Civil Defence controller Garry Towler said the impending weather system is likely to bring heavy rain and have severe coastal impacts.
"We are consulting with our coastal scientists on this one because it does appear there will be some storm surge, and on top of what's already occurred in the last week, it could be problematic.
"We are just getting our heads around that. We are working with our coastal scientists over the weekend and early next week and just trying to get as prepared as we can."
Weta Cafe owner Sallie Budden said holidaymakers have left Coromandel in droves in the last few days as heavy rain and strong winds battered the region.
"Last night it quietened down because obviously the coast road was down to one lane because a tree fell down, and, Whitianga, the hill, you couldn't get to Whitianga.
"A lot of people did leave. I mean, understandable, they had kids, and you know, campgrounds and what-not, but we certainly noticed the town's so quiet at the moment."
Heavy falls are expected in Wairarapa and Hawkes Bay from this afternoon.
Southeast winds are also expected to strengthen across northern Marlborough and about Nelson with a risk they could reach severe gale in exposed places from this afternoon till late Sunday afternoon.
A severe thunderstorm watch remains in place for Coromandel Peninsula and most of the central North Island, from midday until 10am Sunday, with downpours bringing up to 40mm of rain per hour.
The area has become sodden under days of heavy rain.
MetService meteorologist Angus Hines said another big weather system was due mid next week.
"It's another low coming in from the north, and this one has the potential to pack a real punch once again. It could bring some more heavy rain and some strong winds to the Coromandel Peninsula."
Hines said its path over New Zealand was not yet certain.
"There's a chance that it might swing a little bit away and miss Coromandel, but there's just as much of a chance that it could bring another couple of days of very wet weather to that part of the nation."
Thames Valley civil defence controller Garry Towler said a number of local roads were already closed due to slips and the catchments saturated.
"We're expecting these slips and trees to come down for the next four or five days."
If the weather system did arrive in the Coromandel it would "possibly cause further delays and more flooding and further slips".
He advised any holidaymakers returning to the area to "drive to the conditions" and "add time to your journey" because there may well be delays.
RNZ
