Staggering rainfall difficult to predict
ALTHOUGH meteorological services were forecasting heavy rain for Auckland days in advance, officials say the scale of its record rainfall ‘‘couldn’t have been predicted’’.
On Friday, Tā maki Makaurau experienced its wettest day on record, with severe flooding that claimed three lives. A fourth person is missing.
Hundreds of people had to be rescued from their homes, workplaces and cars, trapped by floodwater, slips and fallen trees, and water and wastewater operations remain ‘‘significantly’’ impacted.
MetService meteorologist Angus Hines said the forecast heavy rain featured in its severe weather outlook early last week, and was reflected in severe weather watches and warnings from Thursday onwards.
Rain began before sunrise on Friday, and MetService issued an ‘‘orange’’ heavy rain warning for the entirety of the day – warning of a risk of thunderstorms and isolated downpours.
At 9.10am on Friday, MetService issued a severe thunderstorm watch for Northland and Auckland. This warned that downpours could be severe.
It advised rainfall of this intensity could cause surface and/ or flash flooding, especially in low-lying areas, and slips. It advised of potentially hazardous driving conditions. It continued to reissue severe weather advisories for Tā maki Makaurau throughout the day. Things quickly escalated: Rainfall across Auckland turned ‘‘extreme and unprecedented’’, Hines said.
With torrential downpours not abating, MetService – in consultation with Auckland Council – elevated the warning to ‘‘red’’ (issued only in the most extreme weather events) – for the entire region.
Auckland Emergency
Management deputy controller Rachel Kelleher said agencies work closely with MetService to understand the likely severity of these events. However, ‘‘the intensity of Friday’s event escalated rapidly, and localised rain rates were unprecedented’’.
Kelleher says the agency acted as soon as it received intelligence that the storm was escalating, setting up its Emergency Coordination Centre by 5pm.
‘‘Our response teams were quickly deployed and worked alongside our emergency service partners to respond to what has been a devastating storm event,
‘We had to find emergency centres in a matter of minutes.’ ANDREW CLARK, EMERGENCY MANAGEMENT CONTROLLER
the size of which couldn’t have been predicted.’’
Kelleher says the activation and response was ‘‘well under way’’ before a local state of emergency was declared by Auckland mayor Wayne Brown about 9.30pm.
While a declaration affords the agency more powers, such as enforcing evacuations if needed, ‘‘it does not signal the start of a response’’.
‘‘Our focus was, and continues to be, on supporting Aucklanders who have been impacted.’’
Yesterday, Emergency Management controller Andrew Clark said the event was beyond anything the city had ever seen.
The priority was rescuing people and finding shelter for those who had been displaced, and ‘‘we had to find emergency centres in a matter of minutes’’.
Hines said the ‘‘extremely torrential’’ rainfall amounts recorded were ‘‘unprecedented’’ for Auckland’s weather stations.
The Auckland Airport weather station has had an unbroken record of observation since 1962. Before Friday, its record for the wettest day was 161.8mm of rain.
Between 9am Friday and 9am yesterday, the same site recorded 245mm – surpassing the record by more than 50%.
Hines said forecasters can never really be totally sure of the extent of a severe weather event until they start to see what is happening at weather stations.
‘‘We knew of the risk . . . but you can never be sure of the exact extent.’’