The rough weather forecast for many parts of the country is beginning to set in, with two days of persistent rain expected in Canterbury, which could cause rivers to burst their banks.
MetService meteorologist Tom Adams said the Nelson-Tasman region has been particularly hard hit so far.
"We've seen some stations, particularly in the Takaka Hill region, that have seen over 100 millimetres in the last 12 hours.
"Canterbury, on the other hand, the heavy rain warning only started at 3pm today.
"We've seen 30 millimetres or so falling in some of the Canterbury stations but that's very small change compared to what they're expected to see over the next two days."
However, the region is next in line - with 200 to 300 millimetres expected to hit the High Country.
"That's a lot of rain to be falling in the hills and while we are expecting smaller amounts down at lower levels obviously those rivers are going to swell and we are going to see flooding and potentially inundations downstream as those rivers start to rise."
In the seaside suburb of Sumner, local authorities have delivered sand bags to businesses on the main road in case a combination of king tides and rain sends water through the town centre.
There has been some rain in the area, though not a lot. But one local said they are bracing in case it becomes worse.
MetService issued a red warning for severe weather for Canterbury, south of Amberley, for the weekend, with 200 to 300mm of rain forecast for the high country, and 80 to 120mm about the plains and the coast.
Peak hourly rates of 10 to 20mm/h are expected, especially from later on Saturday and during Sunday.
North Canterbury and the Kaikōura coast were expected to be the worst affected, with other parts of Canterbury also in for wet and windy conditions.
An orange warning for heavy rain is in force for the region from Amberley to Kaikoura. From 3pm on Saturday until 3pm on Monday, 150 to 200mm of rain is forecast. Peak rates of 10 to 20mm/h expected on Saturday evening and during Sunday.
The rain is expected to cause dangerous river conditions and significant flooding. Slips and floodwaters are likely to disrupt travel, making some roads impassable and possibly isolating communities.
Rivers of concern include the Ashley, Selwyn, Ashburton, Opihi and Orari, along with the tributaries that flow into those rivers. River flows will be highest on Sunday and Monday.
Niwa is forecasting a rapid increase in river flows across Canterbury.
HEAVY SNOW
MetService also advised that the freezing level was forecast to be around 1400 metres on Saturday, then lifting to around 1800 metres on Sunday, before lowering to 1400 metres again on Monday.
Heavy snow is expected above the freezing level throughout the event, but it may fall as low as 1000 metres in some places at times, especially on Saturday and Monday.
Snow is expected to continue to affect alpine passes on state highways on Saturday and Sunday, MetService said.
Lewis Pass (SH 7): From 11am until 2pm, snow may affect the road until early this afternoon, and 1 to 3cm could settle on the road near the summit during this time.
Arthur's Pass (SH 73): From 8pm on Saturday until 10am on Sunday, snow is expected to affect the state highway. Expect 1 to 3cm of snow to settle on the road near the summit, with lesser amounts down to 800 metres during this time.
Porters Pass (SH 73): From 8pm on Saturday until 10am on Sunday, snow is expected to affect the road from this evening through to Sunday morning. Expect 1 to 3cm of snow to settle on the road near the summit, with lesser amounts down to 800 metres during this time.
Weather commentator Richard Green told RNZ's Checkpoint programme on Friday that he put the forecast weather for Canterbury in the "severe category".
"It is very rare that Canterbury has a ... red alert status from MetService. It's the terminology ... things like 'dangerous river conditions and flooding are expected', 'slips and floodwaters are likely to disrupt travel for Cantabrians, some roads impassable' and 'possibly floodwaters isolating communities'.
"That's terminology I've never come across from MetService. We don't want to push the panic button here, but to give you an idea how heavy this rain is looking, it's starting mid-afternoon, late afternoon tomorrow and it's falling on very dry ground, we're in drought territory here and the amount of rainfall ... in the alps is not unusual.
"However, it's what's falling across the plains, coast and maybe Christchurch - 80 to 120mm, now, this year so far we have had for some parts of north Canterbury, 30mm. We're looking at trebling that or quadrupling that in 48 hours."
Green advised keeping an eye on the Canterbury rivers and said farmers would be preparing by moving stock to higher ground.
"This is significant, it's not to be sneezed at... this is first red alert for Canterbury that I have seen from MetService."
He pointed out that the alert was for 44 hours.
"If it does go on for that long, there could be significant problems."
Waka Kotahi New Zealand Transport Agency's senior manager maintenance and operations Wayne Oldfield said the rain had potential to cause widespread flooding, land instability and for some rivers to break flood banks.
Christchurch City Council said the city might escape some of the worst of the rain, but with king tides also expected, measures would be put in place to reduce the flood risk.
Contractors were clearing grates and making checks on the stormwater network, the council said.
People in Canterbury were being encouraged to clear out drains and gutters before the heavy rain arrived.
Fire and Emergency NZ recommended that if people had not cleaned out their spouting, gutters and drains recently, now would be a good time to do it.
It also said that if water leaked through light sockets, to turn off the power as short circuits could cause fires.
- RNZ and ODT Online
