Comparison of Tropical Cyclone Wind Radius Estimates between the KMA, RSMC Tokyo, and JTWC

Abstract

This study compared estimates of gale-force wind radii (R30 or R34) and storm-force wind radii (R50) of tropical cyclones (TC) by three agencies—the Korea Meteorological Administration (KMA), the Regional Specialized Meteorological Center (RSMC) Tokyo, and the Joint Typhoon Warning Center (JTWC)—in the western North Pacific during 2015–2018 and investigated the characteristics of these estimates. The results showed that the KMA’s R30 and R50 estimates were smaller (38% and 29%, respectively) than those of the RSMC Tokyo, and larger (11%) for R30 and smaller (12%) for R50 than those of the JTWC. The differences between these agencies seem to be largely determined by whether the agency estimates wind radii based only on a TC’s own winds or on TC winds combined with other mid-latitude synoptic systems to make TC warnings more comprehensive. The former is mainly the practice of the KMA and JTWC, whereas the latter is mainly the practice of the RSMC Tokyo. The factors considered for estimating wind radii also differ between the agencies: the KMA heavily relies on TC intensity—the higher the intensity, the larger the radius—while the RSMC Tokyo and JTWC rely less on TC intensity than the KMA but additionally consider the latitude and storm translation speed in their estimations. In particular, the TC translation speed considered by the RSMC Tokyo and JTWC explains why their estimated wind radii exhibit, on average, greater asymmetries (i.e., greater differences between the longest and shortest radii) than those estimated by the KMA. The findings of agency-dependent characteristics of TC wind radius data help to better determining and understanding the TC impact areas for TC risk reduction and management.