Evaluation of tropical cyclogenesis in operational global models and their ensembles

In 2009, the National Hurricane Center (NHC) began issuing probabilistic forecasts of tropical cyclogenesis on an operational basis for the Atlantic and eastern Pacific Ocean basins. These forecasts are based on a variety of observational and forecast data, including numerical model forecasts. In this paper, we examine the ability of operational global models and their ensembles to predict genesis at lead times out to ten days during the 2008 and 2009 hurricane seasons.

We will present results for forecasts of genesis in the Atlantic, eastern Pacific and western Pacific Ocean basins. For 2008, we will include the high resolution deterministic forecasts from the NCEP Global Forecast System (GFS), the Meteorological Service of Canada (MSC) GEM model, and the ECMWF model. In addition, the forecasts from the lower resolution ensemble forecasts will be evaluated for each of these Modeling Centers. The GFS and MSC ensembles are each comprised of 20 members, while the ECMWF ensemble has 50 members. For 2009, we will also include an evaluation of the FNMOC/NOGAPS deterministic model and the 16-member FNMOC global ensemble forecast system.

The use of an ensemble allows for the development of an ensemble-based probabilistic genesis forecast. Statistical evaluations such as Brier Skill Scores and reliability diagrams will be presented. These measures will be compared against those computed for the NHC official forecasts.