Multimodel Superensemble Forecasting of Tropical Cyclones in the Pacific

Abstract

Using currently available operational forecast datasets on the tracks and intensities of tropical cyclones over the Pacific Ocean for the years 1998, 1999, and 2000 a multimodel superensemble has been constructed following the earlier work of the authors on the Atlantic hurricanes. The models included here include forecasts from the European Centre for Medium-Range Weather Forecasts (ECMWF), the National Centers for Environmental Prediction/Environmental Modeling Center [NCEP/EMC, the Aviation (AVN) and Medium-Range Forecast (MRF) Models], the U.S. Navy [Naval Operational Global Atmospheric Prediction System, (NOGAPS)], the U.K. Met Office (UKMO), and the Japan Meteorological Agency (JMA). The superensemble methodology includes a collective bias estimation from a training phase in which a multiple-regression-based least squares minimization principle for the model forecasts with respect to the observed measures is employed. This is quite different from a simple bias correction, whereby a mean value is simply shifted. These bias estimates are described by separate weights at every 12 h during the forecasts for each of the member models. Superensemble forecasts for track and intensity are then constructed up to 144 h into the future using these weights. Some 100 past forecasts of tropical cyclone days are used to define the training phase for each basin. The findings presented herein show a marked improvement for the tracks and intensities of forecasts from the proposed multimodel superensemble as compared to the forecasts from member models and the ensemble mean. This note includes detailed statistics on the Pacific Ocean tropical cyclone forecasts for the years 1998, 1999, and 2000.