Sensitivity of 96 and 120-hour Numerical Model Tropical Cyclone Position Forecasts to Initial Position Errors

Abstract : Global Forecast System (GFS) western Pacific tropical cyclone track forecasts from the 2011, 2012, and 2013 seasons (87 storms) were compared to Joint Typhoon Warning Center (JTWC) tropical cyclone best track data and warning bulletins in order to determine the sensitivity of 96 and 120-hour tropical cyclone position forecasts to initial position error. A tropical cyclone vortex tracker, which uses seven different model parameters to track storm centers, was implemented to determine model forecast positions. The differences between JTWC analysis positions and the model-derived vortex positions were analyzed at each forecast hour (00, 12, 24, 36, 48, 72, 96, and 120). The relationship between the geographical spread among the model vortex-tracking parameters and forecast errors was also considered. Correlations between error at each forecast hour and the initial 00-hour error suggest that position error has no effect on forecast error at 96 and 120-hours.