Recurving western North Pacific tropical cyclones and midlatitude predictability

Abstract

Data from an ensemble prediction system are used to examine the impact of recurving tropical cyclones on downstream midlatitude forecasts. The ensemble spread, normalized by its climatology, increases after recurvature and peaks approximately 4-5 days later. It returns to climatological levels within a week after recurvature. Initially, the spread increases around the position of the tropical storm. Subsequently, it increases after extratropical transition, and it is associated with a developing wave packet in the midlatitude storm track. The enhanced spread propagates downstream approximately at the group speed of the wave packet. These results suggest that relative to the model's baseline, recurvature-related increase in loss of forecast skill is spatially and temporally localized. Further, energy dispersion of the developing wave packet may constrain the rate at which the forecast errors propagate downstream.