Brief communication: Forecasting extreme precipitation from atmospheric rivers in New Zealand

With mountainous topography and exposure to mid-latitude westerly storms causing frequent atmospheric river landfall and associated hydro-hazards, medium-range forecasting of extreme precipitation is a critical imperative for New Zealand. Here, the European Centre for Medium-Range Weather Forecasts Extreme Forecast Index (EFI) is applied to two variables in forecast week 2, total precipitation (TP-EFI) and vertically integrated water vapour transport (IVT-EFI). Results reveal the TP-EFI sometimes outperforms the IVT-EFI in capturing extreme precipitation events – in contrast to past Europe-based research and indicating a need to develop further our conceptual understanding of the predictability of extreme precipitation in different geographical contexts.