Extreme Rainfall over Coastal Eastern Asia Arising from Interactions between a Monsoon Gyre, Four Tropical Cyclones, and Mobile Midlatitude Disturbances in Late August 2016

Four Tropical Cyclones (TCs; Kompasu, Mindulle, Lionrock and TD-14W) developed from cyclonic vortices embedded in a broad monsoon gyre that formed over the subtropical western Pacific in mid-August 2016. TC Lionrock was especially noteworthy for two reasons. First, TC Lionrock was an intense cyclone that formed via the tropical transition (TT) process, a pathway that is less common in the western Pacific as compared to the North Atlantic basin. Second, TC Lionrock had multiple interactions with TCs Mindulle, Kpmpasu, and TD-14W that had a significant impact on its track. TC Lionrock formed southeast of Japan on 19–20 August via the TT process. TC Lionrock subsequently moved southwestward while remaining well east of Taiwan as it engaged in a “Fujiwhara-like” cyclonic motion with TCs Kompasu, Mindulle, and TD-14W that moved around to the east.

TC Lionrock subsequently made a tight cyclonic hairpin turn, turning northeast prior to undergoing a strong extratropical transition (ET) as it interacted with an unusually deep and intense baroclinic trough. TC Lionrock’s ET was also noteworthy because the storm took a Sandy (2012)-like “left hook” towards Japan. This left turn during ET culminated in multiple extreme precipitation events occurring in conjunction with a predecessor rain event (PRE) and devastating flooding over parts of eastern Asia in late August 2016.

TC Lionrock’s remarkable life cycle from its initial formation by the TT process to its concluding strong ET that was accompanied by a “left hook” toward Japan, analogous to TC Sandy’s now-infamous “left hook” to the New Jersey coast on 31 October 2012, motivates several science opportunities. These opportunities include: (1) investigating the structure and evolution of monsoon gyre formation and the resulting multiple TC interactions with this gyre, (2) the ET of TC Lionrock and its role in the observed extreme precipitation events over eastern Asia, and (3) and the cumulative downstream impacts of these TC, gyre, and mid-latitude interactions, including the strong ET of TC Lionrock. These science opportunities are motivating our investigation of the remarkable life cycle of TC Lionrock from its birth by the TT process to its death via the ET process.