On the Sharp Track Change and Rapid Intensification of SuperTyphoon Chanchu (2006)

SuperTyphoon Chanchu (2006) was well known as a strong TC, with the maximum surface wind of 50 m s-1 and the minimum sea-level pressure of 930 hPa. Its peak deepening rate is about 1.7 hPa h-1 and 12 m s-1 per day during the period of 1800 UTC 13 – 1200 UTC 14 May 2006. It could be considered as a marginally rapid intensifying (RI) TC by the definition of (Kaplan and DeMaria 2003). The storm entered the SCS on 13 May and landed in the coast of Southern China on 18 May. It was also the worst and most intense typhoon on record to enter the SCS in May. As Chanchu moved northward, it began to interact with a low-level cold front on 15 May, and an upper-level jet on 16 May – a subject for ET Chanchu was blamed for several hundred deaths and several hundred million dollars in damage in the Philippines, China, and in the South China Sea. The sharp northward turn on 15 May was unanticipated by over 300 Vietnamese fisherman who were left stranded in Chanchu's path and killed (see http://english.vietnamnet.vn/reports/2006/05/573957/ ). Some studies have been conducted on Chanchu such as the genesis of Chanchu from a westerly wind burst at the equator during the MJO (Hogsett and Zhang 2010, 2011). Mao and Wu (2008) suggest that Chanchu served as the trigger for the onset of the 2006 Asian monsoon.

In this study, an 8-day nested-grid numerical simulation with the Advanced Research Weather Research and Forecast model (ARW-WRF) is used to examine the sharp track change, rapid intensification and extratropical transition (ET) of SuperTyphoon Chanchu (2006). Results show that the WRF model reproduces well the track and intensity of Chanchu, especially its sharp northward turn, and landfall at China's southern coast, although the simulated storm moves faster than the observed at the later stage. Deep-level mean flow shows that the steering flow play an important role in the sharp track change, while the upper-level warm core explains the rapid intensification of the storm. Chanchu's interaction with the cold front accounts for the ET, leading to the transformation of an upright to a tilted warm-core structure, a more axisymmetric to high-asymmetric rainfall structure, and finally a baroclinic system (after the termination of the model integration).