The Predictability of the Extratropical Flow Response to Recurving Atlantic Tropical Cyclones

Abstract

AbstractGiven the ability of recurving Atlantic tropical cyclones (TCs) to disturb the amplitude of Rossby waves on the extratropical jet, this study investigates whether the predictability of the synoptic-scale flow is significantly modified from climatology downstream from and after TC recurvature events. Predictability is evaluated as the standard deviation of isentropic potential vorticity among a 50-member ensemble and is compared to a model climatology. It is shown that forecast uncertainty is dependent upon the relative location of the nearest trough at the time of recurvature and the relative zonal speed between the aforementioned trough and the TC in the 72 hours after recurvature. Predictability is significantly degraded when recurvature occurs downstream of a trough; the elevated uncertainty subsequently propagates downstream along with the trough axis. Furthermore, this study evaluates predictability in spectral space in order to distinguish between uncertainty tied to the exact location of troughs and ridges and uncertainty in Rossby wave amplitude. The wavelet analysis demonstrates that the increase in uncertainty is not solely limited to the trough location, as there is also significantly elevated uncertainty in the Rossby wave amplitude that originates from the upstream trough and spans across downstream troughs and ridges. Uncertainty is also increased near the recurvature longitude in the subset of cases in which the Rossby wave train propagates zonally slower than the TC after recurvature, which is hypothesized to be linked to baroclinic growth processes.