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

With mountainous topography and exposure to midlatitude westerly storms causing frequent atmospheric river landfall and associated hydrohazards, medium-range forecasting of extreme precipitation is 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. Importantly, these case studies highlight the need to develop further understanding of sources of predictability for extreme precipitation in different geographical contexts.