Tropical Cyclone Gale Wind Radii Estimates for the Western North Pacific

Abstract

AbstractThe Joint Typhoon Warning Center?s (JTWC) forecast improvement goals include reducing 34-kt (1 kt = 0.514 m s?1) wind radii forecast errors, so accurate real-time estimates and postseason analysis of the 34-kt wind radii are critical to reaching this goal. Accurate real-time 34-kt wind radii estimates are also critical for decisions regarding base preparedness and asset protection, but still represent a significant operational challenge at JTWC for several reasons. These reasons include a paucity of observations, the timeliness and availability of guidance, a lack of analysis tools, and a perceived shortage of personnel to perform the analysis; however, the number of available objective wind radii estimates is expanding, and the topic of estimating 34-kt wind radii warrants revisiting. In this work an equally weighted mean of real-time 34-kt wind radii objective estimates that provides real-time, routine operational guidance is described. This objective method is also used to retrospectively produce a 2-yr (2014?15) 34-kt wind radii objective analysis, the results of which compare favorably to the postseason National Hurricane Center data (i.e., the best tracks), and a newly created best-track dataset for the western North Pacific seasons. This equally weighted mean, when compared with the individual 34-kt wind radii estimate methods, is shown to have among the lowest mean absolute errors and smallest biases. In an ancillary finding, the western North Pacific basin average 34-kt wind radii calculated from the 2014?15 seasons are estimated to be 134 n mi (1 n mi = 1.852 km), which is larger than the estimates for storms in either the Atlantic (95 n mi) or eastern North Pacific (82 n mi) basins for the same years.