Prediction of Extreme Rainfall in the Tropical Southwest Pacific using a Poor Man's Ensemble

The Australian Bureau of Meteorology uses a poor man's ensemble (PME) to produce operational rainfall forecast guidance for the Australian continent. The PME takes forecasts from seven NWP models, and computes the average rainfall, and probability of rainfall exceeding pre-defined thresholds.

Recently the PME domain was extended to cover the tropical Southwest Pacific in order to provide experimental forecast guidance to the WMO Severe Weather Forecasting and Disaster Risk Reduction Project (SWFDDP). Quantitative and probabilistic forecasts of rainfall from the PME were verified against observations from several Southwest Pacific islands.

Our results show the PME provides useful guidance for rainfall occurrence and amount at most of the tropical island locations, with PME equitable threat scores comparable to or better than from the Bureau of Meteorology's operational NWP model. The PME has a tendency to under-forecast extreme rain events because not all the component NWP models have severe weather systems co-located (or present). Some preliminary results demonstrating the use of probabilistic forecasts from the PME to address this issue will also be shown.