West Coast deluge nears Christchurch's annual rainfall, half of Auckland's

Tuesday, 26 March 2019

The volume of rain pounding Milford Sound during the storm battering the South Island is nearing what Christchurch sees in an average year. 

It comes as Westland is in a state of emergency due to risk to people and property, and the Waiho Bridge, south of Franz Josef, has been swept away by a river in raging flood. 

National Institute of Water and Atmospheric Research (Niwa) figures show about 530 millimetres of rain has dropped at Milford Sound since Sunday night, with more expected overnight.

Comparatively, Christchurch averages about 650mm a year while Auckland and Wellington sees about 1250mm annually. But for Milford Sound it's just a drop in the bucket; the area averages 6000-7000mm a year.

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The rest of the West Coast has gotten off slightly lighter; 494mm has fallen at Mueller Hut, 459mm at the Ivory Glacier, 391mm at Mt Cook and 206mm at Mt Philistine.

MetService meteorologist Melissa Oosterwijk said about 265mm had fallen at Franz Josef, while about 350mm had dropped at Mt Aspiring.

Oosterwijk said the rain was 'a significant event' but not unheard of; these volumes were considered a one-in-20-year event for Westland and a one-in-two-year event for the Southern Alps.

Westland Mayor Bruce Smith declared a state of emergency on Tuesday evening due to 'raised risk of life and injury for local residents and further risk to property'.

A welfare centre has been set up in Haast Hall to host those whose properties have been flooded by 'minor breaches' from the Haast River. About 50 people, mainly tourists, were staying at the hall.

The weather has closed several major roads in the region, including 360km of State Highway 6 between Makarora and Hokitika. 

The rain, caused by a cold front from the south, has begun to ease in Fiordland and would ease on Wednesday morning in Westland. 

A weather warning was in place for Buller from 11pm Tuesday night, expected to ease about midday Wednesday. Oosterwijk said the region has had occasional rain so far but could expect it to be heavier overnight. 

As of Tuesday night, warnings also remained in place for Westland and the Canterbury headwaters.