Statistical Postprocessing of NOGAPS Tropical Cyclone Track Forecasts

Abstract

A statistical postprocessing technique is developed and tested to reduce the U.S. Navy global model (NOGAPS) track forecast errors for a sample of western North Pacific tropical cyclones during 1992?96. The key piece of information is the offset of the initial NOGAPS position relative to an updated (here best-track) position that will be known by 6 h after the synoptic times, which is when the NOGAPS forecast is actually available for use by the forecaster. In addition to the basic storm characteristics, the set of 24 predictors includes various segments in the 0?36-h NOGAPS forecast track as well as a 0?36-h backward extrapolation that is compared with the known recent track positions. As statistically significant regressions are only found for 12?36 h, the original 36-h to 72-h NOGAPS track segment is simply translated to the adjusted 36-h position. For the development sample, the adjusted NOGAPS track errors are reduced by about 51 n mi (95 km) at 12 h, 35 n mi (65 km) at 36 h, and 28 n mi (52 km) at 72 h. Independent tests with a 1997 western North Pacific sample, 1995?97 Atlantic sample, and 1996?97 eastern and central North Pacific sample of NOGAPS forecasts have similar improvements from the postprocessing technique. Thus, the technique appears to have a more general applicability to Northern Hemisphere tropical cyclones.