Tropical Cyclone Gabrielle has been upgraded to category 3 and MetService forecasts it will develop into category 2 tomorrow.
As of Friday morning, it was moving southeast over open waters in the Coral Sea and was close to reaching its peak intensity, MetService said.
NIWA said the weather system - which was expected to hit from Sunday and last until Tuesday - was tracking further east than it had been yesterday but that continued to expose Auckland, Northland, Coromandel, Bay of Plenty and Gisborne to the impacts.
It is likely to hit Northland some time on Sunday, before moving towards Auckland and the Coromandel Peninsula.
MetService's advisory on Friday morning said maximum winds near the centre of the cyclone were estimated to be about 120 km/h, with gales extending up to 370km from the centre.
"It is expected to be located about 550km to the far southwest of New Caledonia tonight [Friday], then move southeast and out of the tropics early Saturday.
"Strong and possibly gale force winds, heavy rain and large waves are expected to affect exposed parts of New Caledonia and southern Vanuatu for a time from Friday evening through to Sunday."
Then from Sunday through Tuesday, it was highly likely Northland, Auckland and Coromandel Peninsula would be exposed to severe gales, MetService said.
"Also from Sunday through Tuesday, there is high confidence of significant heavy rainfall over Northland, Auckland, Coromandel Peninsula, and Gisborne," MetService said in its severe weather outlook on Friday.
"This high confidence extends to Bay of Plenty, Gisborne and easternmost Waikato on Monday and Tuesday, when there is also low confidence for Taranaki, Waitomo, Taumarunui, and the remainder of Waikato."
The @niwa_nz ensemble system shows a range of possible cyclone track scenarios.— NIWA Weather (@NiwaWeather) February 9, 2023
A gentle nudge east-or-west makes all the difference in which regions experience the worst weather!
Heavy rain, damaging winds & coastal hazards are looking likely in the north & east... pic.twitter.com/e04fgwg64y
Large waves and a storm surge are expected to affect northern and eastern coastlines from Northland to Gisborne from Sunday into Monday, spreading south to Marlborough on Tuesday.
Mayors and Civil Defence authorities across the upper North Island have been warning residents to be prepared and keep an eye on the forecast.
Auckland and Thames-Coromandel on Thursday extended their state of emergency due to the risks.
Australia's Norfolk Island was also bracing for impact from overnight on Saturday.
Australia's Bureau of Meteorology warned: "Gabrielle is a very large cyclone having gale-force winds and high waves extending much further from the centre than a typical cyclone."
We've just issued Heavy Rain and Strong Wind Watches for Sunday 12th through to Wednesday 15th, covering areas likely to see impacts from Tropical #CycloneGabrielle— MetService (@MetService) February 9, 2023
Head to https://t.co/qHyE5zzql5 for the full details. pic.twitter.com/3yDZsWHZlD
Coromandel coastal areas likely to evacuate
Coromandel Civil Defence said it was likely some low-lying coastal communities would need to be evacuated or be advised to self-evacuate before the cyclone hits the region.
Thames-Coromandel Civil Defence Controller Garry Towler said a final decision on any evacuations would be made later today.
''The message we will be giving those communities is be quite strong and so we want to make sure of our facts and that the impacts will be what they are going to be. We are just tidying up the forecast and working with MetService before we announce the communities that we want to focus on to prepare," Towler said.
''The last thing we want to do on the Coromandel is have to go in and evacuate people under an emergency situation. It is very dangerous for rescue staff.''
Once the storm hits, access around the Peninsula would be very limited, with the roading network still suffering damage from a storm two weeks ago, he said.
''The message to all people is prepare yourselves. If you are in a vulnerable area, then go to family or friends in a safer place and ride it out, or, if you can't do that, then get in touch with Civil Defence, so that we can help you the best we can.''
Towler said storm surge on the east and west coasts of the peninsular could result in flooding of many beachside areas.
Up to 300mm of rain is expected on the Coromandel Peninsula between Monday and Wednesday.
Cyclone Gabrielle will be the fifth severe storm to hit Coromandel since November 2022.
Putting out sandbags
Further south, on the east coast, Gisborne District Council is warning residents in low-lying areas to stock up on supplies ahead of the cyclone.
MetService has issued a weather watch for the region this morning, with between 200mm and 400mm of rain set to fall in Tairāwhiti between Sunday and Tuesday.
Tairāwhiti Civil Defence Controller Ben Green said the biggest risks were slips and dropouts cutting off access to some homes.
Contractors are putting out 300 sandbags around the city in flood-prone areas, and council staff are also doing pre-storm checks of vulnerable properties.
In Auckland, where residents have been told to be ready evacuate at short notice and ensure they have three days worth of food and water, the Sandbag Store is down to selling empties but these have nearly run out.
Auckland Council is urging people to take flood-damaged items from the recent downpour to one of its 15 drop-off spots before Sunday as teams from council and the defence force race to remove kerbside piles.