Hundreds of homes are without power and campgrounds are emptying in Te Tai Tokerau amid non-stop rain and wind.
The Thames-Coromandel Council is also urging holiday makers to make plans and act quickly before an intense five-day storm hits the region.
MetService duty forecaster Jessie Owen told Morning Report weather warnings and watches were in place for much of the northwestern regions of the North Island and top of the South Island.
This morning, more than 500 properties lost power in North Hokianga, and smaller outages affected Awanui, Waikare, Kerikeri, Ruakākā and Kauri.
Stong wind gusts have caused a small number power outages across Auckland.
Vector said trees or branches falling on power lines were responsible for many of the outages, mainly concentrated in the north and western parts of the city.
Gusts are expected to reach 100km/h in Northland today. The region's heavy rain warning for is in place until tomorrow morning, with expectations of 110 to 160mm of rain accumulating, mainly in the north and east.
MetService said the eastern hills may see accumulations of 200 to 250mm but peak rates of 20 to 30mm per hour were expected from Wednesday night.
Northland has so far seen rain accumulation of 40 to 50mm overnight, and MetService said more was on the way.
"We have a low pressure system sitting out to the northwest of the country and that's directing a strong northeasterly flow across the top of the North Island at the moment and that's going to be moving slowly across the country," Owen said.
"Unfortunately, we've got a big high-pressure system sitting out the east, and that's preventing it from making much progress, so it's going to be sitting over us for a couple of days and that's going to be bringing strong northeasterly winds and heavy rain to many parts of the country."
A heavy rain watch is in place for Auckland including Great Barrier Island, Coromandel Peninsula, Bay Of Plenty west of Matatā, and Tasman northwest of Motueka.
A strong wind watch is in force for Northland, Auckland including Great Barrier Island, Waikato, Coromandel and western Bay of Plenty to Taranaki and Taihape.
Whangaruru Beachfront Camp and Motel owner Robynne Cooper said winds of "around 50 knots" on Monday saw tents starting to rip and awnings shred.
Yesterday, a few planes had to turn around from Wellington Aiport due to changing wind directions near the runway, Owen said.
Matakana's Summer Haze concert, due to start on Wednesday, was also cancelled due to the stormy weather forecast.
Wind and waves are increasing at our east-facing camera at Bream Bay in Northland. ️
— NIWA Weather (@NiwaWeather) January 3, 2023
The upper North Island will continue to see strengthening easterlies over the next 24-36 hours with heavy rain on Wednesday. ☔ pic.twitter.com/WW7ZxoxgKD
Warning of five-day storm
Residents and holidaymakers in Coromandel are being urged to make plans and act quickly before an intense storm hits the region.
The Thames-Coromandel District Council issued the warning through its website and social media this afternoon.
It said a five-day storm was expected to hit the Coromandel.
Civil Defence controller Garry Towler advised everyone to err on the side of caution and plan ahead to Sunday.
Towler said five more days of northeasterly wind and rain on Coromandel was likely to have a wide impact.
He urged people to go to a secure location, or even head home until the storm passes.
Gale-force winds at beaches expected
Surf Life Saving is warning holidaymakers across the North Island to take extra care at beaches over the coming days.
Surf Life Saving said gales and surging swells were expected this week on eastern and western coastlines.
Spokesperson James Lea said many beaches were already experiencing moderate to gale force winds and choppy surf.
Eastern coastlines from Northland to the Coromandel can expect heavy swells that may not ease until Friday.
Lea is asking people to monitor the Safeswim website for updates, and to stick to patrolled beaches for water-related activities.
Campers flee before storm hits
Hundreds have reportedly left campsites in the region after hearing about the incoming bad weather.
Bland Bay campground manager Wayne Johnstone said he had a huge hit to his books as holidaymakers cancelled.
Just 45 people were left on his site, and most people who had booked for this week and next had cancelled, Johnstone said.
This year was already shaping up to be a bad one financially, he said.
"Usually we would have around 300 to 350 people here with us but the weather has put an end to that. So approximately two days ago, they started leaving in anticpation that the weather was going to turn bad."
On the other hand, his site had not seen flooding yet.
Puriri Bay Campsite manager Joanne Cairns said after hearing weather warnings, many campers had decided to leave early.
"A lot of our sites are a bit damp. We've had a lot of people leave. We must have had about 35 to 30 groups leave, we have 85 sites there so we've got a half-empty [campsite], it was fully booked."
Manager of Treasure Island camp, at Pātaua South, Jenna Whaikawa said sites were normally booked out at this time of year, and leading up to summer, some people had to be turned down.
"We've basically had a mass exodus from the campgrounds. So we have had about more than 70 percent of those that were booked for this period, leave."
Most campers were from Auckland, Whaikawa said.
"We are almost fully booked at least 10 months ahead."
Normally that meant more than 500 people were purchasing goods and takeaways from the camp shop - but not now.
"I've had to cut down rosters for starters," Whaikawa said.
"So it means all staff basically have received half the amount of shifts as we've almost halved the number of staff that will be required per day.
"This essentially means that everything that was purchased to stock the shop, and the takeaways, is not being sold, and therefore, we've bought stock that we can't sell."
Most of those who had stayed on camping were in campervans, Whaikawa said, but she was optimistic people would continue to keep coming annually.
"We have long-term campers that have stayed for 37 years. We have people that have come for the last 10, 15, 20. And they know and like this place, and they just come back every year, regardless of what's going on."
Police are advising motorists in Northland to take extra care on the roads this evening.
MetService asked travellers to stay up to date with forecasts.