A Diagnosis of the Poorly Forecast Interaction between Recurving Tropical Cyclone Malakas (2010) and the Extratropical Flow

In late September 2010, recurving Tropical Cyclone (TC) Malakas interacted strongly with the extratropical flow as it underwent extratropical transition over the western North Pacific. The interaction amplified a Rossby wave train that dispersed rapidly downstream. When the Rossby wave train reached North America, it established a high-amplitude ridge–trough pattern that was associated with record-breaking heat in western North America and flooding rains in portions of eastern North America. The timing and amplitude of this Rossby wave train was poorly forecast by NCEP deterministic and ensemble prediction models for lead times as short as three days.

It is hypothesized that the large-scale flow amplification was highly sensitive to the timing and strength of the TC–extratropical flow interaction. To evaluate this hypothesis, the main modes of extratropical flow variability associated with the recurvature of TC Malakas (i.e., the main forecast scenarios of recurvature) are identified by applying an empirical orthogonal function–fuzzy clustering analysis (Harr et al. 2008; Anwender et al. 2008) to THORPEX Interactive Grand Global Ensemble (TIGGE) forecasts of potential temperature on the dynamic tropopause over the North Pacific. Then, the TC–extratropical flow interaction is objectively evaluated following Archambault et al. (2013) for each forecast scenario of recurvature. Finally, for each forecast scenario of recurvature, the large-scale flow response to Malakas is evaluated in terms of the timing and strength of the corresponding TC–extratropical flow interaction.