Impact of ensemble composition, formulation, and resolution on tropical cyclone track forecast performance

A number of configurations of the NOGAPS Ensemble Transform (ET) ensemble forecasting system were run for July-October 2008, and the tropical cyclone (TC) track forecasts of the ensemble members and the ensemble means were evaluated for the Atlantic and North Pacific basins. Experiments were run testing ensembles with different formulations, different number of members, and different resolutions. It was found that increasing the NOGAPS forecast model resolution from T119 to T159 had a positive impact on the TC track forecasts of the ensemble members as well as the ensemble mean. For forecast lengths greater than 24 h, increasing the resolution resulted in a reduction in the ensemble mean TC track forecast error of roughly 10 percent for the combined Atlantic and North Pacific basins. The number of members required to produce an optimal ensemble mean was also reduced by the increase in resolution.