Typhoon Morakot meteorological analyses

Typhoon Morakot yielded record-breaking precipitation and caused severe disasters in Southern Taiwan in early August 2009. This event revealed the desperate need for extreme rainfall and disaster prediction. The multiscale analysis on circulations demonstrates that Typhoon Morakot not only developed in a monsoon trough, which is a large-scale system in favor of the development of convection systems, it was also involved with complicated features of different scales that included typhoon circulation itself, the circulation of northwestward-propagating 10–30-day oscillation, and the circulation of northward-propagating 40–50-day oscillation. The other remarkable features of Typhoon Morakot are: the asymmetric structure of convection, less damage occurred near the typhoon center than at the fringes, and the record-breaking torrential rain in the mountain areas of south Taiwan induced by the flows on the south fringe of the typhoon. The causes of disastrous precipitation from Typhoon Morakot can be stated as: (1) a large-scale environment in favor of convection development and a plentiful vapor supply provided by strong southwesterly flow, (2) the interaction between topography, typhoon circulation, and large-scale circulation resulting in the heavy rainfall in the mountains of Southern Taiwan, and (3) the weakening of steering flow slowed down Morakot's translation speed before it made landfall and extended the duration of heavy precipitation.