Recurving Tropical Cyclone–Extratropical Flow Interactions and their Influence on the Large-Scale Flow Pattern: A Diagnostic and Modeling Study

As a tropical cyclone (TC) undergoes recurvature, its diabatically driven divergent outflow may interact with the extratropical flow such that a jet streak develops and/or an upper-level ridge amplifies. In some instances, the TC–extratropical flow interaction can excite or amplify a Rossby wave train, leading to the onset of large-scale circulation anomalies well downstream of the TC. Due to the inherent complexity of TC–extratropical flow interactions and their sensitivity to diabatic processes, which may be inadequately resolved by numerical models, the predictability of the large-scale flow pattern often is reduced during TC recurvature episodes.

In late October 2010, a complex and poorly forecast interaction between recurving western North Pacific TC Chaba and the extratropical flow helped to initiate a Rossby wave train that dispersed rapidly downstream to North America. The subsequent establishment of a high-amplitude ridge–trough pattern over North America provided favorable synoptic conditions for extreme heat over western North America and heavy rain over eastern North America.

The objective of this study is to identify the physical and dynamical mechanisms that link the interaction between TC Chaba and the extratropical flow to the large-scale flow reconfiguration and high-impact weather that occur downstream. Diagnostic analyses and high-resolution numerical simulations produced by the WRF-ARW will be used to examine the relative roles of precipitation within the core of TC Chaba versus frontogenetically forced precipitation along a developing baroclinic zone just poleward of Chaba in driving divergent outflow that interacts with the extratropical flow. Of particular interest with respect to frontogenetically forced precipitation associated with the recurvature of TC Chaba is the role of a diabatic Rossby vortex-like disturbance originating along the baroclinic zone poleward of Chaba in (i) forming a jet streak via its divergent outflow and (ii) serving as a precursor to subsequent explosive extratropical cyclogenesis over the eastern North Pacific.