Predictability of a Predecessor Rain Event over Northeastern Japan Associated with Recurving Typhoon Roke (2011)

Tropical cyclones (TCs) that recurve over western portions of ocean basins can enhance the potential for remote heavy rain [i.e., >100 mm (24 h)^-1] associated with mesoscale convective systems. Such rain events, termed predecessor rain events (PREs), are favored to occur when moist air surges poleward from a TC and ascends along a low-level baroclinic zone within the equatorward entrance region of an upper-level jet streak.

Whereas several studies have addressed the synoptic conditions favoring PREs, relatively few studies have focused on the predictability of PREs. To this end, this study evaluates the predictability of a PRE that occurred over northeastern Japan during 17–18 September 2011 in association with recurving Typhoon Roke. Uncertainty in the characteristics of the PRE (i.e., its intensity, location, and timing) is assessed with respect to uncertainty in (i) the corresponding track of Typhoon Roke and (ii) the corresponding synoptic conditions over eastern Asia and the western North Pacific in the period surrounding the PRE.

To address (i), the PRE characteristics in THORPEX Interactive Grand Global Ensemble (TIGGE) are evaluated with respect to the corresponding location of Typhoon Roke within TIGGE. The location of Typhoon Roke in TIGGE is defined using probability ellipses, which contain 68% of the TIGGE members (Pearman 2011). To address (ii), the PRE characteristics in TIGGE are evaluated with respect to the main synoptic forecast scenarios found to contribute to the variability in TIGGE. These forecast scenarios are obtained by applying an empirical orthogonal function–fuzzy clustering analysis to TIGGE geopotential height fields (i.e., Anwender et al. 2008).