A new statistical ensemble prediction system (STEPS) for the track and intensity (defined as maximum wind speed) of tropical cyclones is presented. The system is based on a statistical analysis of the annual performance of all available operational numerical prediction models, assuming that their position and intensity errors are systematic and depend on storm structure, location and motion. For a given tropical cyclone advisory and given model forecasts of a particular storm at any base date and time, the statistical analysis of the model performances in the year preceding the base date and time can be used to produce a track and intensity prediction and probability distributions of future storm positions and intensities at all prediction times.

The statistical ensemble prediction system was developed using all available tropical cyclone advisories, model predictions and "best track" positions and intensities of all Atlantic Hurricane seasons between 1996 and 2000. Track and intensity predictions were carried out for each individual year between 1997 and 2000. The 12, 24, 36, 48 and 72 h mean position errors, averaged over the whole time period 1997-2000, were found to be 66, 120, 167, 215 and 296 km, respectively, and correspond to positive skill (negative relative error) of about 20% relative to all high-quality numerical models and the National Hurricane Center's (NHC) official forecast at all prediction times. The corresponding errors in maximum wind speed were found to be 3.3, 5.5, 7.5, 9.2 and 10.7 m/s and had approximately the same quality as those of the official forecast of the NHC.

A major advantage of the new track and intensity prediction system lies in the automatic production of geographical strike probability maps and intensity probability intervals. Mean 1997-2000 diameters of the 66.7% strike probability regions of 139, 274, 389, 535 and 749 km and 66.7% intensity probability intervals of 9.0, 13.5, 17.5, 20.9 and 25.7 m/s at 12, 24, 36, 48 and 72 h prediction time, respectively, show the potential of the new system with regard to operational tropical cyclone track prediction.