Relationship between Tropical Cyclone Development Pathways and Extratropical Transition

This study analyzes the relationship between tropical cyclone development pathways and the probability of extratropical transition (ET). That is, we ask the question: is ET more likely for storms whose original development occurs via one pathway vs. another? We considered tropical cyclones globally in the period 1979 – 2010 using best-track datasets from the National Hurricane Center (North Atlantic and eastern North Pacific) and the Joint Typhoon Warning Center (western North Pacific, North Indian Ocean and southern hemisphere). Extratropical transition occurrence was determined by Hart’s Cyclone Phase Space (CPS), as described in Bieli et al. (2019). The genesis development pathway of each storm was defined by McTaggart-Cowan et al. (2012), using the following categories or pathways: non-baroclinic, low-level baroclinic, trough induced, weak tropical transition (TT) and strong TT. In each basin, we determined the rate of occurrence of ET (both in absolute terms and as a fraction of all storms) for each development pathway. We further analyzed the ET occurrence and fraction as functions of seasonality, interannual variability, and storm tracks. The differences in ET rates between genesis pathways are statistically significant in a few cases. For instance, in the North Atlantic, the strong TT pathway has an ET fraction of 79.6% while the ET fraction of all other pathways is 53.0%, yielding a 99% significance level in the difference in ET fraction. In the western North Pacific, the trough induced pathway has ET fraction of 55.3% while the ET fraction of all other pathways is 43.8%, yielding a 95% significance level in the difference in ET fraction. Globally, the strong TT and trough induced pathways have ET fractions that are statistically significantly different from all other development pathways.