Recurving Tropical Cyclones as Precursors to Blocking

High-latitude blocking is a subseasonal atmospheric phenomenon that has been linked to high-impact weather such as flooding rains, heat waves, and cold-air outbreaks. The hypothesis that the recurvature of tropical cyclones (TCs) over the western North Pacific favors the onset of high-latitude blocking is explored from statistical and dynamical perspectives. This hypothesis is based on the tendency for recurving TCs over the western North Pacific to induce Rossby wave dispersion and cyclonic wave breaking, two processes linked to high-latitude blocking.

In this study, a standard blocking index is used in conjunction with a database of recurving TCs over the western North Pacific to assess the frequency of blocking episodes following recurving TCs, and, conversely, the frequency of TCs preceding blocking episodes. In addition, composite analyses are constructed from the 0.5° NCEP/NCAR Climate Forecast System Reanalysis data to establish the dynamical mechanisms and physical processes linking recurving TCs to the onset of blocking. It is found that blocking tends to occur a wavelength or more downstream from the recurving TC within the poleward exit region of an elongated, intensified North Pacific jet steam, where cyclonic wave breaking is favored. Furthermore, the phasing between TC outflow and extratropical features over the western North Pacific is found to influence whether a jet stream configuration that is favorable for blocking develops downstream of a recurving TC.