Decadal behaviors of tropical storm tracks in the North West Pacific Ocean

Abstract

Quantitative analysis on the shape of 959 tropical storm (TS) tracks in the North West Pacific (NWP) basin was carried out over the period from 1977 to 2016 by using International Best Track Archive for Climate Stewardship (IBTrACS) provided by National Oceanic and Atmospheric Administration (NOAA) based on an established track sinuosity metric. Track sinuosity is a measure of deviation of a storm track from its straight–line path between the cyclogenesis and cyclolysis locations. More sinuosity in the storms' tracks makes it rather challenging for the atmospheric models to accurately assess the storms' respective locations on the map and potentially causes higher damages due to lack of precise information about their movement. Statistical analysis was carried out on spatial and temporal trends (monthly to decadal) of the TS track shape and the obtained results were mapped based on sinuosity categories within a GIS environment. The sinuosity distribution results are normalized using a cube–root transformation function to reduce skewness and obtain sinuosity index (SI). Distinct enhancement of TS sinuosity was noticed from the months July to October (JASO). It is also detected that early months of TS season like June–August have dominance of more predictable straighter storm tracks over sinuous kind of tracks, and vice-versa in the case of late months of season like September–October. It is also evident that there is a one- to three-year cyclic pattern of changing sinuosity over the NWP basin. The 1987–1996 decade had the maximum dominance of sinuous tracks in comparison to the other three decades. Significant longitudinal eastward shift (from 110°–140° E to 130°–160° E) in majority of cyclogenesis locations is observed as sinuosity in storm track increases from straight to sinuous patterns. Similar shift for latitudinal track was not found. Finally, we investigate the sinuosity based on the warm/cold phase of the ENSO. Warm phase of ENSO is found to be associated with a greater number of TS with higher SI values in the NWP basin. These TS during warm phase mostly originate in the eastern part of the basin where a vast open area of warm sea surface temperature encourages their formation and intensification. Lastly, the study found a moderate positive relationship between SI and TS' longevity and distance coverage, which are crucial information for disaster risk assessment, mitigation and preparedness.