Bay of Plenty Regional Council anticipates rivers will reach the first warning level tomorrow morning, with heavy rain expected to saturate the region.
Police have issued a warning for motorists, the Matahina dam is being lowered and other authorities in the Bay of Plenty are making preparations for the deluge.
MetService has a heavy rain warning in place for the Bay of Plenty, including Rotorua, for a 19-hour period from 8pm tonight to 3pm Wednesday.
"Expect a further 70 to 100 mm of rain, but 150 to 180mm about inland areas east of Whakatane, on top of what has already fallen. Peak intensities of 20 to 30 mm/h in the east Wednesday morning," the warning read as of 8.23pm.
"Heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous."
TC Ruby š
— MetService (@MetService) December 14, 2021
Currently tracking along New Caledonia - hoping everyone was as prepared as possible!
Good news is it's moving quite quickly and continues its southeast track away from Noumea overnight.
Current information keeps it well away from NZ https://t.co/7wKJumwhyP pic.twitter.com/h2OiwT7OIg
Regional council duty flood manager Mark Townsend said Trustpower had been instructed to lower the Matahina dam as a precaution.
"We anticipate that all rivers will reach Level 1 tomorrow morning."
The first warning level means the river level has reached its normal channel capacity and triggers messages to landowners to move stock from low-lying river-adjacent areas.
Townsend said the council is closely monitoring rain and water levels.
"The situation is changing constantly, but at this stage, MetService forecasts indicate the bulk of the heavy rain will arrive tomorrow morning.
"In line with these projections, we're looking to activate our Flood Room at around 8am tomorrow morning and have a number of staff on stand-by should the situation escalate."
Townsend said peak flows are forecasted to arrive in the various rivers from Wednesday afternoon through to Thursday morning.
A Metservice warning is also in place for the Coromandal Peninsular from 6pm tonight to 4am tomorrow, with 70 to 90mm of rain expected to accumulate and peak rates of 10-20mm/h about the ranges.
Rotorua Lakes Council said it was keeping an active watch on the current weather warnings and relevant teams were on standby to respond to weather-related issues or emergencies.
Council staff and contractors have been checking all major stormwater pipe inlets to make sure they're clear of debris, emptying storage ponds at the Wastewater Treatment Plan and in the forest as much as possible to ensure maximum capacity, double-checking equipment, ensuring all Emergency Operations Centre and Civil Defence staff rosters and contingency plans were in place and all communication lines were open and ready.
Support crews were also on standby if more help is required. Checks will also take place again once the rain clears, the council said.
The council had a small number of weather-related calls today, mostly for trees down and slips with additional support crews from Fulton Hogan on standby for the next couple of nights.
All Rotorua Lakes Council sports fields were closed on Tuesday afternoon.
Tauranga City Council general manager of community services Gareth Wallis said the council was "carrying out all our usual checks for when there's significant rain on the radar".
These included sending its maintenance contractor to check sumps in areas known to flood with heavy rainfall.
Wally Potts, the council's drainage services team leader, said a heavy rain checklist was made prior to any predicted rain event and performed again at the end of the event.
"This is predominantly for inlets and outlets with a history of blocking with debris that is mobilised in a storm."
"Poor weather reduces visibility and increases stopping distances, so remember to watch your following distances when in traffic and drive at a speed appropriate for the conditions," a spokeswoman said.
"It's also a timely reminder to do the basics to keep yourself and other motorists safe - make sure everyone is wearing their seatbelts, put the phone away, and don't drive while impaired."
MetService Meteorologist Amy Rossiter said warm days and humid nights are set to continue as a northerly flow pulls warm, moist sub-tropical air down over the country.
"These humid air masses are quite dynamic and can hold a lot of moisture, therefore producing significant rainfall rates. We are already seeing pulses of heavy rain affecting the upper North Island," Rossiter said.
UPDATE (Tues 10:20am): The timing of the warning has been pushed back- we can expect the heavy rain to start this...
Posted by Bay of Plenty Civil Defence on Sunday, December 12, 2021
Other regions with a heavy rain watch now are the north and east of Northland, Eastern Waikato and TaupÅ, Gisborne north of Tokomaru Bay and from north Taranaki (except the mountain) to Waitomo and across to inland Whanganui and Taihape.
The heavy rain and increasingly humid conditions over the last few days come as a newly named Tropical Cyclone Ruby has been located over the Coral Sea.
Low pressure zones in the #TasmanSea are siphoning some of the energy from #CycloneRuby. This increases the chances of heavy, tropical, downpours over parts of #NewZealand over the next few days with #Flooding risks. We'll have more details this morning.https://t.co/gb7E1qcpZ3. pic.twitter.com/iZRrsek7cX
— WeatherWatch.co.nz (@WeatherWatchNZ) December 13, 2021
Its latest position is about 650km northwest of New Caledonia, as of this morning, and is moving southeast.
WeatherWatch head weather analyst, Philip Duncan, says it is currently a category 2 strong cyclone, but has the potential to become more fierce.
It is set to head over New Caledonia and some southern parts of Vanuatu tonight, before tracking towards New Zealand, Duncan said.
MetService says it is expected to intensify to a category 3 event as it moves across New Caledonia tomorrow.
By Saturday, however, weather experts expect that the cyclone's tropical characteristics will wane as it comes into contact with cooler seas.
"On Thursday, the system is expected to move southeast past the upper North Island as a deep low.
"Most outlooks suggest the system will remain offshore to the north of the North Island, but there remains some uncertainty regarding how close to New Zealand the system will come."
Next week, an atmospheric river of moisture may flow southward into Aotearoa New Zealand, as a tropical cyclone swirls to the north
There's a strong chance for a wetter than normal week across the North Island, with a risk for heavy rainfall that may lead to floodingpic.twitter.com/pfcyakXULt