Watch: Canterbury conditions to get worse before they get better - MetService

Persistent heavy rain and widespread flooding in Canterbury is set to get worse before it gets better, MetService says. 

Heavy rain has been piling up in the region over Saturday night and Sunday morning causing flooding, shut roads and burst river banks. Timaru, Ashburton and Selwyn have been forced to declare a state of emergency.

MetService is maintaining its red-alert severe weather warning for Canterbury saying conditions "will get worse before they get better". 

MetService meteorologist Angus Hines says red warnings are "only issued for the most extreme weather systems which cause widespread disruption and severe impacts".

Hines says that while there has been a "little easing" of rain through north Canterbury, heavy rain persists through mid and south Canterbury due to a low targeting the area.

"It's all due to this broad low which is just stamped across Aotearoa. The centre of it is up over the North Island but the bigger impacts, the real sting of the tail is coming with the strong south-easterly down south." 

The red-alert warning is set for Canterbury south of Amberly and is in place until 11am on Monday, according to MetService. 

Between Sunday afternoon and Monday morning a further 70, 80 or 100mm of rain "may be possible" for low-lying parts of Canterbury and the Canterbury coastline, Hines says. 

"Inland a further 150 to 200mm could be experienced in the Canterbury high country and around the foothills.

"So we are expecting conditions to worsen through Sunday, rivers will continue to rise, more rivers may burst their banks, flooding is expected to get worse both inland and near the coast, several roads are already shut but more could be added to the list." 

Hines also warns those near the coastline to beware of the incoming high tide as it may worsen flooding.

"For those of you on the coast, high tide tonight 8pm, that is gonna lift the water level, the rivers running high as well that could exacerbate flood risk for coastal Canterbury this evening." 

An orange warning is still in place for north Canterbury. While rain has subsided, it is expected to return overnight, Hines saying this area could see another 100 to 150mm of rain by 3pm Monday.

Watches have also been introduced for north Otago, Dunedin, Southland and Clutha, the regions are expected to see a "heavy dose" of rain late Sunday and early on Monday. 

Strong south-east gales are set to continue to batter the South Island. 

Hines saying they will be "strongest on both coastlines where severe gales could rise to 120km through Westland, south of Hokitika, Fiordland and along the east coast as well." 

He advises Canterbury residents to avoid travel unless they are leaving a flood area, a full list of road closures can be viewed here.