A Comprehensive Analysis of Recurving EPAC Tropical Cyclones in Environments of Upper-Tropospheric Troughs

Eastern North Pacific tropical cyclones (EPAC TCs) can significantly impact North America's west coast, leading to challenges such as urban and agricultural flooding. Most often observed in September, these landfalling EPAC TCs are often associated with nearby upper-tropospheric troughs, typically inducing southwesterly flow over the TCs. While upper-tropospheric troughs are typically characterized by increased vertical wind shear and dry air, their interactions with TCs in the western Atlantic and Pacific basins have occasionally led to intensification through increased upper-level divergence in the right entrance and left exit regions of upper-tropospheric jet streaks and an increase in angular momentum eddy flux convergence in the TC outflow layer. This study aims to acquire a better understanding of the structures of upper-tropospheric troughs and their relative dynamic contributions to the evolution of EPAC TCs.

To examine the structures of upper-tropospheric troughs and their relative dynamic contributions to the evolution of EPAC TCs, we will use 6-hourly best-track data (1950–2022) from the National Hurricane Center's HURDAT2. This data will be utilized to locate and extract maximum sustained surface wind and minimum central surface pressure for EPAC TCs that minimally reach tropical storm intensity. We will quantify the distribution of maximum upper-tropospheric potential vorticity anomalies surrounding an EPAC TC to objectively define TC-trough interactions with ERA5 reanalysis data (e.g., Fischer et al. 2019). Subsequent quasi-geostrophic analyses on these patterns, incorporating low-level warm-air advection and moisture flux convergence, will aid in comprehensively evaluating the strength and duration of dynamic interactions between EPAC TCs and upper-tropospheric troughs. We will present a case study illustrating our methodology and showcasing a notable instance of a favorable EPAC TC-trough interaction, enhancing the generality and applicability of our findings with practical insights into our approach.