Ensemble Forecast Experiment for Typhoon Quantitatively Precipitation in Taiwan

The continuous torrential rain associated with a typhoon often caused flood, landslide or debris flow, leading to serious damages to Taiwan. Therefore the quantitative precipitation forecast (QPF) during typhoon period is highly needed for disaster preparedness and emergency evacuation operation in Taiwan. Taiwan Typhoon and Flood Research Institute (TTFRI) started the Taiwan Cooperative Precipitation Ensemble Forecast Experiment (TAPEX) in 2010. The ensemble members include various models and consider different setups in the model initial conditions, data assimilation processes and model physics.

The results of TAPEX from 2010~2013 show that the ensemble mean provides valuable information on typhoon track forecast and quantitative precipitation forecasts around Taiwan. For example, the ensemble mean track captured the sharp northward turning when Typhoon Megi (2010) moved westward to the South China Sea. The model rainfall also continued showing that the total rainfall at the northeastern Taiwan would exceed 1,000 mm, before the heavy rainfall occurred. Similar situation occurred for Typhoon Nalgae (2011) which caused 1,621 mm accumulated rainfall during a 72-hours period (1~3 Oct) in I-lan area. Although the ensemble forecast performs reasonably well for the total rainfall amount during the typhoon period, it still has limitation especially the short-duration extremely heavy rainfall occurred over a small area which will be discussed in the presentation.