Civil Defence is warning residents in the upper North Island, including Auckland, to brace for more severe weather today as rainfall totals reach uncharted levels.
As the shocking wet spell shows no sign of abating, Coromandel and the Bay of Plenty are being warned to expect up to a month's worth of rain today - on top of the month's worth that has already fallen across the saturated regions this week.
Niwa is describing the rain that fell in Auckland's Hunua Ranges as "off the chart" and well above a one-in-100-year event.
The torrential downpour left swathes of southern Auckland and the Coromandel under water, closing roads and forcing people to evacuate their homes.
Four schools and five early childhood centres have closed across Northland, Coromandel and southeast due to flooding, and roads across the region are still affected.
MetService meteorologist Georgina Griffiths said further bursts of heavy rain are expected in the Auckland region between now and Sunday.
"While we've had a good, dry reprieve today, the weather on Friday night and Saturday morning is forecast to be comparable to, or worse, than Tuesday."
Localised downpours are possible anywhere in the region today and tomorrow, especially overnight.
Niwa meteorologist Ben Noll described the volume of rain that fell in the upper Hunua Ranges overnight Tuesday as "off the chart".
"According to Niwa's high-intensity rainfall system model, the volume that fell - 225mm in 12 hours - well exceeds what would be considered a one-in-100-year event. It's off the chart," he said.
"And it's not over yet. We're expecting more deluges [today] and into the weekend."
Today authorities are concerned about how this will affect already-saturated eastern areas of Auckland, including Waiheke Island, Clevedon Valley and the Hunua Ranges.
This morning MetService issued thunderstorm and heavy rain warnings for the top of the country.
Watch out for a few thunderstorms this afternoon for the top of the country. https://t.co/BZWb7ZPiRd ^JR pic.twitter.com/0WAdishUif
— MetService (@MetService) March 9, 2017
Auckland Civil Defence emergency operations manager Aaron Davis said the agency was monitoring the situation and encouraged people to have a weekend inside.
Debris and flooding would be affecting roads and people were urged to drive with extreme care. Davis warned people to not attempt to drive through floodwaters.
"At this stage it is hard to be certain about which areas of the region are likely to be hit with the most rain, but you should consider your plans for the weekend, especially if you are likely to be driving," he said.
Many roads that were closed on Wednesday had reopened today but motorists were warned to drive with caution and watch for slips and surface water. JV Grant Rd in Wellsford was closed after a large tree came down and sections of Twilight Rd in Clevedon and Kawakawa Bay Coast Rd were still impassable because of flooding.
MetService meteorologist Peter Little said a warning was in place for heavy rain in Coromandel from midday and Bay of Plenty from about 3pm.
Little said both regions could expect 120mm to 140mm of rain in that time.
"You're in for another month's worth of rain again in that period," he said. "The ground is going to be getting a lot more rain yet before it can dry out."
This morning the Ministry of Education said Motatau, Waima and Maromaku Schools were closed in Northland after floodwaters cut off roads. Karangahake School in Thames was also closed. Four early childhood centres in the Coromandel Peninsula and one in Kawakawa Bay had also not opened today.
Tapapakanga Regional Park, Hunua Ranges Regional Park and Waitawa Regional Park have been closed because of heavy flooding.
Aucklanders are also being asked to reduce their water use over the next three weeks after floods affected capacity at Ardmore Water Treatment Plant.
About half of Auckland's water comes from four water storage dams in the Hunua Ranges, where flash flooding has taken place.
Watercare chief executive Raveen Jaduram said Aucklanders needed to reduce their water consumption by 20 litres a day, "until the silt in the dams settle and we can resume normal production at our Ardmore plant".
Because of flash flooding, the Ardmore Water Treatment Plant was treating about half the water it usually did.
A small number of properties in southeast Auckland have been damaged and flooded. Those affected should contact their insurance company.
Meanwhile, in Coromandel, roads were closed yesterday and road crews were clearing debris and preparing for more heavy rain.
Road crews dealt with about 30 incidents on state highways in the area on Wednesday, ranging from major slips that brought down power lines to minor flooding.
NZTA regional performance manager Karen Boyt said workers were still trying to clear the damage.
"It's a big job and we'd like to thank the Coromandel people for being so patient while we work to get their roads cleared," Boyt said.
She asked that motorists watch their speed and drive carefully.
"We know that there is more heavy rain forecast to fall on the Coromandel for Friday and over the weekend so we will have our crews in a state of readiness should more slips and flooding occur."
Northland was hit by thunderstorms and torrential rain overnight, but no damage was reported, despite predictions of downpours of 30-50mm an hour.
• Whangarei
Friday - Periods of rain, chance of heavy and thundery falls. Strong northeasterly.
High 25C, overnight low 20C
Saturday - Periods of rain, heavy at times. Northerlies.
High 27C, overnight low of 20C
Sunday - Periods of rain, chance of being heavy, but easing. Northwesterly.
High 27C, overnight low 19C
• Auckland
Friday - Periods of rain, chance of heavy and thundery falls. Strong northeasterly.
High 25C, overnight low 19C
Saturday - Periods of rain, heavy at times. Northerlies.
High 26C, overnight low 20C
Sunday - Periods of rain, chance of being heavy, but easing. Northwesterlies.
High 25C, overnight low 19C
• Hamilton
Friday - Rain at times, chance of heavy and thundery from afternoon. Northeasterly wind.
High 24C, overnight low 18C
Saturday - Rain, heavy falls, chance of thunderstorms. Northerly winds.
High 26C, overnight low 19C
Sunday - Periods of rain, chance heavy. Winds turn northwest.
High 25C, overnight low 17C
• Tauranga
Friday - Periods of rain, chance of heavy and thundery falls.
High 23C, overnight low 20C
Saturday - Rain, heavy falls, chance of thunderstorm. Northerly winds.
High 25C, overnight low 20C
Sunday - Periods of rain, chance heavy. Winds turn northwest.
High 25C, overnight low 19C
• Napier
Friday - Mostly cloudy, periods of rain from morning. Northeast.
High 23C, overnight low 18C
Saturday - Periods of rain. Northerlies.
High 26C, overnight low 18C
Sunday - Rain at times. Winds turning southerly.
High 26C, overnight low 18C
• Wellington
Friday - Occasional rain from late morning. Light winds.
High 24C, overnight low 15C
Saturday - Periods of rain, chance heavy. Winds turn southerly.
High 19C, overnight low 14C
Sunday - Periods of rain, chance heavy. Strong southerly gale.
High 18, overnight low 14
What you need to know
• Heavy rain expected in Auckland between now and Sunday
• Take extreme care driving through heavy rain. Do not drive through floodwaters
• State Highway 25 at Whangamata remains closed because of a number of large slips
• Aucklanders are being asked to reduce their water use over the next three weeks after floods affected water treatment capacity
• Consider alternative plans if you have an outdoor event scheduled this weekend
• If you live on a rural property, think about your livestock rotation for the weekend, especially if your farm is flood-prone
• Check your drains and gutters to ensure these aren't blocked. These can cause flooding issues during heaving rain
• Tapapakanga Regional Park, Hunua Ranges Regional Park and Waitawa Regional Park have been closed because of heavy flooding
Police will co-ordinate rescue operations via other SAR teams and helicopter providers.