Evaluation of Northwest Pacific tropical cyclone track forecast difficulty and skill as a function of environmental structure

Abstract

A Systematic Approach for tropical cyclone track forecasting by Carr and Elsberry defines the Synoptic Environment of each cyclone in terms of ten Synoptic Pattern/Region combinations. Because storms in each Pattern/Region combination have characteristic tracks that are dramatically different, it is hypothesized that the degree of difficulty in forecasting the tropical cyclone track, and the skill of the Joint Typhoon Warning Center (JTWC) track forecasts will be a function of the Synoptic Environment. The degree of forecast difficulty is defined by comparing forecast track errors (FTEs) of the operational CLImatology and PERsistence (CLIPER) technique in each of the ten Pattern/Region combinations with the overall CLIPER FTEs. The most difficult combinations are the recurving scenarios of Weakened Ridge Region of the Standard Pattern and the Southerly Flow Region of the Multiple tropical cyclone Pattern. The least difficult combinations are the Dominant Ridge Regions of the Standard and Gyre Patterns. The JTWC forecasts have statistically significant skill compared to the no-skill CLIPER forecasts for storms in the Standard/Dominant Ridge and North-oriented Pattern/North-Oriented Region, which comprise nearly 77% of the five-year sample of JTWC forecasts. As transitions occur between the Synoptic Pattern/Region combinations, the degree of forecast difficulty increases, and the JTWC forecast skill decreases. Although the JTWC track forecasts are generally slow and slightly to the left, significant differences are found in man of the Pattern/Re ion combinations.