The track forecast error bounds shown on the TSR Storm Tracker represent the mean distance between forecast and actual tropical cyclone positions at all lead times over a number of previous years. These errors are calculated by each tropical cyclone forecasting centre (see the Data document for more about these centres) during the post tropical cyclone season assessment of their forecast performance. The errors represent the average performance of tropical cyclone track forecasts at given lead times in a particular region during previous years. As such they do not indicate a definitive bound on the actual future cyclone position and serve as an indication only.
The table below shows the error values (in nautical miles) used by the TSR Storm Tracker. Note that the 96 h and 120 h lead forecasts for the North Indian and Southern Hemisphere have only been introduced in 2010. The error figures used for these lead times and basins (marked * in the table) represent average errors over the period 2010-2012.
The table below provides a summary of the data available for each tropical cyclone region:
|Region||Mean Position Error for each Forecast Lead Time (nm)||Data Period|
|0 h||12 hrs||24 hrs||36 hrs||48 hrs||72 hrs||96 hrs||120 hrs|
|North East Pacific||10.1||25.9||41.7||55.3||68.9||98.1||134.6||167.1||2009-2013|
|North West Pacific||13||38||60||81||104||155||178||243||2008-2012|