**2. Typhoon cases and numerical simulations**

The numerical experiments in this study include two case studies: Typhoon (TY) Ketsana (2003) with the development of multiple MCSs and Typhoon Dan (1999) with only one MCS involved during its formation. These experiments are then examined to study the difference in the formation time and energy consumption in the two cases. In the simulations for both typhoon cases, the same set of nested domain settings is applied, and the same satellite datasets have been assimilated via the Weather Research and Forecasting Data Assimilation (WRFDA) system.

In the WRF simulation of Typhoon Ketsana, the model's initial and lateral conditions are taken from the National Center for Environmental Prediction (NCEP) final (FNL) analysis data with the outermost lateral boundary conditions updated every 6 h, and the SST data are interpolated to update the sea-surface boundary conditions. The WRF model is initialized at 0000 UTC on October 16, 2003 and integrated for 108 h until 1200 UTC on October 20. Within this model integration period, the WRFDA is used to assimilate QuikSCAT oceanic winds available at 0600 UTC on October 16 and 0600 UTC on October 17, 2003, and SSM/I oceanic surface wind speed and total precipitable water (TPW) available at 1200 UTC on October 17, 2003 into the boundary conditions. These twice daily swaths of QuikSCAT and SSM/I data are extracted from the remote sensing system (RSS) data archive with 0.25° latitude/longitude resolution.

The WRF simulation of Typhoon Dan (1999) is initialized at 0000 UTC on October 1, 1999 and integrated for 120 h until 0000 UTC on October 6. Similar to the case of Typhoon Ketsana, the WRFDA is used to assimilate QuikSCAT oceanic winds available at 0600 UTC on October 1 and 0600 UTC on October 2, and SSM/I oceanic surface wind speed and TPW available at 1200 UTC on October 1 and 12 UTC on October 2 into the boundary conditions.
