Intraseasonal Variability of Recurving EPAC Tropical Cyclones

The eastern North Pacific (EPAC) exhibits the highest density of tropical cyclogenesis among all tropical cyclone (TC) basins. Climatologically, upper-level easterlies at the southern edge of an EPAC subtropical anticyclone centered over Mexico steer a majority of developed EPAC TCs along the North American coastline before tracking westward. A subset of EPAC TCs, however, have been observed to move poleward or recurve inland due to the influence of EPAC troughs and an eastward displaced EPAC subtropical anticyclone that imposes southerly flow over EPAC TCs. The aforementioned EPAC troughs have been linked to upper-tropospheric anticyclonic Rossby wave breaking (AWB) associated with the development of upstream extratropical cyclones and recurving western North Pacific TCs that undergo extratropical transition commonly exhibited in early autumn. Therefore, the purpose of this study is to investigate the dominant large-scale patterns that are conducive for AWB across the North Pacific that can lead to the formation of downstream EPAC troughs that interact with recurving EPAC TCs.

EPAC TCs observed from 1979–2021 during the autumn will be identified using 6-h best-track data compiled by the NHC (HURDAT2). EPAC TCs that undergo recurvature will be extracted from HURDAT2 using the methods detailed in Archambault et al. (2013). Self-organizing maps (SOMs) will be used to objectively classify the associated upper-level patterns at the onset of each TC recurvature using the potential temperature on the dynamic tropopause surface and 500-hPa geopotential height fields derived from global reanalysis datasets (i.e., the National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR)). Recurvature-relative composite analyses of the large-scale flow pattern for each SOM node will be constructed to identify the large-scale flow patterns and Rossby wave breaking events across the NPAC that lead to recurving EPAC TCs. We also plan to utilize a Rossby Wave Breaking (RWB) tracking algorithm (e.g., Bowley et al. (2019)) to capture RWB events conducive for downstream trough formation centered over the EPAC.