Wild weather is expected to wreak havoc along the Bay of Plenty coastline from today. Strong onshore winds meant king tides today and tomorrow coupled with 7m waves posed a threat to many low-lying communities, Niwa said.
The weather threat prompted local authorities to consider closing coastal areas such as Mauao and Mount Maunganui main beach.
Organisers of Beast of a Feast festival have postponed the event to January 13 due to weather.
Mount Maunganui Lifeguard Service general manager Glenn Bradley said lifeguards were actively monitoring the incoming storm.
"We generally don't close the beach but at the moment it looks like large powerful storm surges, mainly on Friday for a short time, and it doesn't look like a good day to be in the water or close to the water's edge.
"If there are really large high seas you can get really strong storm surges."
Bradley said there had been particularly flat conditions over the past few weeks.
"That's going to change pretty quickly over the next 48 hours. We just hope that people are aware of that and exercise caution. We urge people to be very cautious around the water."
Tauranga City Council spokesman Marcel Currin said the parks team was prepared to close Mauao base track if needed and it was important people respected any track closures for their own safety.
"We don't close tracks lightly."
Elsewhere around the city staff and contractors had already checked 60 stormwater grates and were on standby to respond to any events if they escalated.
Most of the predicted rainfall sat within the stormwater network's ability to cope but there was likely to be extra runoff due to dry ground conditions, Currin said.
MetService, which issued a severe weather warning for the region, said the looming weather event was "fairly significant" and the Bay could expect 150mm of rain across the Kaimai and Mamaku ranges and close to 100mm for Tauranga and Whakatane.
Bay of Plenty Regional Council duty flood manager Peter Blackwood said coastal areas and streams around Rotorua, Tauranga and the western Bay of Plenty were expected to be the worst affected.
Campers and others near the coast should also be extra-vigilant of possible inundation and waves.
"This may result in minor river flooding, and some coastal flooding particularly given recent high tides.
"However, based on the expected wind speed, we wouldn't expect any homes to be impacted by waves and coastal flooding."