2020 Volume 98 Issue 4 Pages 821-833
The effectiveness of the probability ellipse for tropical cyclone (TC) track forecasts is investigated with multiple ensembles from the Japan Meteorological Agency (JMA), the European Centre for Medium-Range Weather Forecasts (ECMWF), the U.S. National Centers for Environmental Prediction (NCEP), and the Met Office in the United Kingdom (UKMO). All TCs during the 3 years from 2016 to 2018 are included in the verification. We show that the multiple ensembles composed of these four global ensembles are capable of predicting the situation-dependent uncertainties of TC track forecasts appropriately in both the along-track (AT) and cross-track (CT) directions. The use of a probability circle involves the implicit assumption of an isotropic error distribution, whereas the introduction of the probability ellipse makes it possible to provide information as to which is more uncertain; the direction or speed of TC movement. Compared to the probability circle adopted operationally at JMA, the probability ellipse can potentially reduce the area by 16, 15, and 24 %, on average, at forecast times (FT) of 3, 4, and 5 days, respectively, indicating that narrowing warning areas of TC track forecasts by the probability ellipse enables us to enhance disaster prevention/mitigation measures.