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MetService quizzed on agency's weather warnings during coronial inquest

An example of MetService weather warnings and watches that were in place on 26 and 27 June. Photo: MetService The chief meteorologist for MetService has been quizzed on the agency's colour-coded weather warnings during a coronial inquest into the deaths of 18 people during Cyclone Gabrielle and the preceding Auckland floods. The inquest , which began Monday, is split into two phases. The first will focus on Auckland and the second on Hastings. MetService chief meteorologist Chris Noble was first to give evidence, questioned by the agency's lawyer Nicola Cuervo on the process used to issue a weather warning. He explained that thunderstorm notifications came in three stages: outlooks, watches and warnings. "Outlooks are designed to give a heads-up that severe or impactful weather is coming at some point in the future (usually three to six days)," Noble said. "As the event draws nearer and it becomes more certain we are likely to have weather that reaches the criteria to justify a warning, we'll issue a watch; this is a heads-up we're close to an event and it looks like it could be impactful." The watch would be upgraded to a warning once it became relatively certain that the storm was imminent. Noble also explained the criteria MetService used to rule that a thunderstorm was "severe". "MetService classifies a thunderstorm severe if one or more of the following criteria are met: heavy rain from thunderstorms of 25 millimetres per hour, large hail, strong wind gusts from thunderstorms of 110 kilometres per hour or more, or damaging tornadoes with a wind speed more than 116 kilometres per hour." Flooding on the corner of Seabrooke and Margan Avenues in the Auckland suburb of New Lynn on 27 January 2023. Photo: RNZ/ Josie Campbell Weather warnings were assigned colours from yellow to red to indicate severity, and given the term "broad scale" if they covered an area of 1000 square kilometres. Noble said it was very rare for a weather event to be both on a broad scale and meet the criteria for a red warning. The "broad scale red warning" label was only issued when there was an event with expected severe impacts and a potential threat to life over a significant area, and just 16 of these warnings had been issued since the colour coded system was introduced in 2019. Auckland's anniversary weekend storm was the ninth of these, and Cyclone Gabrielle the tenth, Noble said. He said when the colour coded system was first established, MetService only expected between one to three weather events on that scale each year - but eight had occurred since the start of 2023. Sign up for Ngā Pitopito Kōrero , a daily newsletter curated by our editors and delivered straight to your inbox every weekday.