Non-local Controls on Tropical Cyclogenesis: A Trajectory-based Genesis Potential Index

Abstract

Abstract Tropical cyclone (TC) genesis is initiated by convective precursors or “seeds” and influenced by environmental conditions along the seed-to-TC trajectories. Genesis Potential Indices (GPIs) provide a simple way to evaluate TC genesis likelihood from environmental conditions, but have two limitations that may introduce bias. First, the globally fixed GPIs fail to represent inter-basin differences in the relationship between environments and genesis. Second, existing GPIs are only functions of local environmental conditions, whereas non-local factors may have a significant impact. We address the first limitation by constructing basin- and timescale-specific GPIs ( local-GPI s) over the Eastern North Pacific (ENP) and North Atlantic (NA) using Poisson regression. A sequential feature selection algorithm (SFS) identifies vertical wind shear and a heating condition as leading factors controlling TC genesis in the ENP and the NA, respectively. However, only a slight improvement in performance is achieved, motivating us to tackle the second limitation with a novel trajectory-based GPI ( traj-GPI ). We merge adjacent non-local environments into each grid point based on observed seed trajectory densities. The seed activity, driven mainly by upward motion, and the transition to TCs, controlled primarily by vertical wind shear or heating conditions, are captured simultaneously in the traj-GPI , yielding a better performance than the original GPIs. This study illustrates the importance of seed activity in modeling TC genesis and identifies key environmental factors that influence the process of TC genesis at different stages.