More heavy rain will sweep across Auckland and Northland today after downpours dumped up to 100mm of rainfall overnight.
MetService meteorologist Rob Kerr said a band of heavy rain had swept across the northern half of the North Island overnight, bringing very heavy rain to some places.
"Some of our stations around the northern half of the country have had over 100mm of rain," he said.
Some parts of the Auckland region got up to 70mm of rain in the last 24 hours, with most of the rain falling since 3pm yesterday.
Northern and eastern areas were worst hit, but other areas were spared heavy rainfall, with Auckland Airport getting only 14mm.
In Warkworth, where a large fallen tree was partially blocking State Highway 1 this morning, there had been 40mm of rainfall.
The tree had fallen about 2km south of the satellite station and blocked both lanes.
One lane was now open to traffic, but police have warned of delays while the tree was removed.
The heaviest band of rain arrived about 8pm yesterday. In Kaeo, in the Far North, there was 52mm of rainfall in just one hour.
"And that's an awful lot of rain," Mr Kerr said.
The front that brought the rain was moving off the east of the country this morning, he said.
However, more showers were expected as a broader low moved across the country today.
"Embedded in that is a couple of troughs. The first of those is currently over Whangarei and approaching northern Auckland, and there could be some heavy falls in that, and there could be one or two thunderstorms as well.
"There will be another trough later in the day before things ease off tonight. It will be a bit more showery, rather than a solid band of rain moving over that region, so some places might just miss out, but some places might get some very heavy rain."
Further south, Wellington had a murky start to the day as low cloud moved up the east coast of the country. Mr Kerr said southerlies would pull low cloud and fog into the city this morning.
"And then the winds will get going and it will flush through quite quickly."
In the South Island, cloud in the east should clear, with Christchurch in for fine spells this afternoon.
A cold southerly was expected later tonight, perhaps bringing snow showers to Banks Peninsula.
Heavy rain has also caused issues in the Bay of Plenty today, with surface flooding in Rotorua forcing the closure of SH36 north of the city.
Police said motorists on the Hamurana Rd stretch of the highway, near Keith Rd, were being turned away due to flooding.
Council contractors were arranging for signage and diversions, and motorists were urged to avoid the area.
Police said there were other areas of localised flooding throughout the region and motorists were advised to take extra care.
The MetService this morning warned there was a high risk of thunderstorms for Auckland this afternoon and evening.
Auckland forecaster Georgina Griffiths said it would continue to monitor the development of any severe storms.
"The main risk with the expected thunderstorms is localised heavy rain, with the possibility of downpours of up to 35mm/hr.
"Deluges of this type can cause localised surface flooding, especially given the saturated soils due to recent heavy rain in the region."
WeatherWatch said showers were already forming around the upper North Island early this morning, and the risk of thunder would increase as the day progressed.
The centre of a low was moving in today, which would allow slow-moving showers to build up in size and create heavy localised downpours.
WeatherWatch said it did not anticipate many issues across the upper North Island today, but a warm northerly flow was expected to bring heavy cloud and downpours.
There was a high risk of heavy downpours this afternoon, with a low risk of localised surface or flash flooding.
Tomorrow morning, there would be a risk of fog around Auckland and Hamilton airports. However, southerlies were expected to move in during the morning to clear any possible fog.
Roads, schools closed in Rotorua
Wet weather has caused roads to close, a serious crash, power outages and at least one Rotorua school to close.
A passenger in a car that struck a power pole on Te Ngae Rd this morning has suffered serious injuries.
Police said earlier reports were a single car had struck a power pole just before 10am, bringing three power poles down outside Placemakers, between Sala St and Hamiora Pl.
The driver was initially trapped.
All occupants are now out of the vehicle, however one rear-seat passenger is reported to have suffered serious injuries and has been taken to hospital.
Contractors had isolated power at the scene.
There is widespread flooding in the area and police said this may have contributed to the crash and urged motorists to take extra care and drive to the conditions.
Unison advised it was working on a power outage covering parts of Ngapuna, Lynmore, Okareka and Tarawera and hoped to have supply resumed early afternoon.
Rotorua District Council had activated its emergency operations centre at the council Civic Centre to monitor weather events, although no Civil Defence emergency has been declared.
Rotorua schools were being asked by the police to keep children at school and not send students home early in order to reduce congestion on roads.
* A substantial number of urban and rural roads have been closed or restricted.
* The council is asking residents to stay off roads until the weather improves unless travel is essential. If residents do need to travel they should exercise extreme care at all times.
* As a result of some sewer overflows people should treat any flood water as potentially contaminated, and in particular ensure that children are kept clear of all flooded areas.
State Highway 36 from Tauranga to Ngongotaha is closed at Awahou. The New Zealand Transport Agency's website said there was a detour in place via Hamurana Rd and State Highway 33 and State Highway 30, past the Rotorua Airport.
Rotorua weatherman Brian Holden said there was "quite a downpour" overnight.
"Up until 8am we have had 67.5mm in the last 24 hours, with most of that being overnight, which has doubled our rainfall for the month . . . and it's still bucketing down.