A coroner has criticised MetService's hourly rainfall forecasts in his findings into the death of a schoolboy on a school trip.
The findings questioned the validity of the weather forecaster's updates, which are computer generated and not moderated by humans before being published.
Coroner Alexander Ho criticised the Whangārei School decision to proceed with the Abbey Caves trip in 2023, with an orange heavy rain warning in place for Northland.
He found that the rainfall updates may not have aligned with the true forecast. And he honed in on the hourly forecasts in his findings.
Coroner Ho said in his findings: "The consequences of relying on inaccurate weather data differ depending on the purpose. Not receiving the expected forecast rainfall for one’s lemon tree is inconvenient. Being caught outside in a thunderstorm during a high-risk outdoor activity is dangerous."
Forecast on the day
The forecast on the Tuesday morning of the trip predicted light-moderate rain that was described by a MetService meteorologist as "the type of rain where the absence of a raincoat would start to be felt".
The coroner said the forecast had changed from the previous night's one, which would have been more accurate.
"The 12.5 millimetres of rain which the Monday 9 pm forecast predicted between 1 to 2 pm on Tuesday was no longer," the coroner said. "Instead, the Tuesday morning forecast predicted rainfall of between 1 and 4 millimetres per hour, each hour, between 7 am and 5 pm."
MetService's official forecast for the region that day was: Rain with squally thunderstorms and downpours, clearing late afternoon, but chance of shower remains.
That may not have been the same communication on the platform the Whangārei Boys' teachers checked.
This is because the hourly updates are computer generated and aren't verified against other forecasts before being released. It left potential for there to be inaccuracies between the various MetService forecasts, with not all information aligning.
The coroner was concerned by this.
"This raises the obvious question of why MetService publishes hourly numbers at all."
Although MetService's resources do state possible differences between app, website and true forecasts, the coroner argued it wasn't made clear enough, and might been to blame for the teachers' decision to go through with the trip.
The app's disclaimer was worded differently from the website's which read:
The hourly forecasts above are automatically generated by MetService’s computer weather modelling system. They have not been moderated by MetService’s forecast team. The magnitude & timing of weather events (rain, changes in wind direction and speed) may differ from those described in worded forecasts. The rainfall data is given for the previous two hours.
There was also the issue of members of the public understanding the hourly rainfall updates, with many people misinterpreting the intended hours.
The coroner explained MetService's hourly forecast observations published on their app and website referred to the time leading up to the present hour, not for the time afterwards.
"In other words, for an observation or forecast published in the '9 am' column, the relevant observation or forecast rainfall is for the hour leading up to 9 am, not the observation or forecast rainfall at 9 am. Nor, as might be inferred, is it for the hour following 9 am," the coroner said.
It was advised that MetService should make definitions and disclaimers in these cases more prominent to help the wider public who may not have full knowledge of how their resources work.
"I recommend that MetService explore the possibility of changing, clarifying or adding elements to its website to improve the dissemination of its weather information, in accordance with the matters discussed in these findings," the coroner said.
"Additionally, it would be sensible, and reduce the risk of confusion, to ensure the wording of disclaimers align between the website and the app."
'Prominently displayed'
MetService chief meteorologist Chris Noble said in a statement that any weather warnings in place should have been heeded over other provided forecasts.
"MetService Severe Weather Watches and Warning should always take precedence over other forecast information," Noble said.
"Watches and Warnings are prominently displayed across our website and app to help people recognise when severe weather is expected and take appropriate action."
Noble said they had already been working on aspects of their communication when the coroner released his findings.
"We have reviewed the coroner’s findings and recommendations which build on improvements that were already being implemented," Noble said.
"Ongoing improvements aim to help people better understand the different types of forecasts and warning information and how they should be interpreted, particularly when severe weather has the potential to create hazardous conditions."
Since the incident, MetService has introduced a message on its website saying:
The hourly model data shown can differ from the written forecast and icons, which are produced by MetService meteorologists and take into account model data along with many other data sources. If they differ significantly, please use the text forecasts.
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