Important Factors in the Tracking of Tropical Cyclones in Operational Models

Multiple configurations of the Geophysical Fluid Dynamics Laboratory vortex tracker are tested to determine a setup that produces the best representation of a model forecast tropical cyclone center fix for the purpose of providing track guidance with the highest degree of accuracy and availability. Details of the tracking algorithms are provided, including descriptions of both the Barnes analysis used for center fixing most variables and a separate scheme used for center fixing wind circulation. The tracker is tested by running multiple configurations on all storms from the 2015-17 hurricane seasons in the Atlantic and eastern Pacific basins using forecasts from two operational National Weather Service models, the Global Forecast System (GFS) and the Hurricane Weather Research and Forecasting Model (HWRF). A configuration that tracks only 850-mb geopotential height has the smallest forecast track errors of any configuration based on an individual parameter. However, a configuration composed of the mean of 11 parameters outperforms any of the configurations that are based on individual parameters. Configurations composed of subsets of the 11 parameters and including both mass and momentum variables provide results comparable to or better than the full 11-parameter configuration. In particular, a subset configuration with thickness variables excluded generally outperforms the 11-parameter mean, while one composed of variables from only the 850-mb and near-surface layers performs nearly as well as the 11-parameter mean. Tracker configurations composed of multiple variables are more reliable in providing guidance through the end of a forecast period than are tracker configurations based on individual parameters.