Extended range forecast of intraseasonal variability of western north Pacific monsoon and typhoons in 2004 using a global nonhydrostatic model

Intraseasonal variability of western north Pacific monsoon modulates large scale circulations, active convective regions and track and number of tropical cyclones. In August of 2004, monsoon trough is extended to the east of Philippine and eight typhoons are generated. In this study, a series of extended range forecast experiments of western north Pacicfic interseasonal variability and typhoons are performed by the global Nonhydrostatic ICosahedral Atmospheric Model (NICAM). The model is initialized 00UTC each day of August 2004 using the ERA-Interim reanalysis data and integrated for 30 days without any convective parameterization schemes at 14-km horizontal resolution. The NICAM well simulated the time series of western north Pacific monsoon index (WNPMI) in the first two weeks. In the latter two weeks, the NICAM well simulate the time variation of WNPMI with a bit underestimation. Almost all runs underestimated WNPMI monsoon index around 25 August in which two typhoons exists near Taiwan and about 2000 km east of Taiwan, respectively since the model failed to simulate them near observed position. The NICAM also well simulate northward shift of active convective region during August and its dissipation in September. Although the NICAM tend to generate typhoons earlier than observed genesis time, the NICAM can predict TC genesis about 10 days in advance. For example, in TC Aere's case, low level vertical disturbance originated from the easterly wave, eastward extension of monsoon trough, and energy dispersion from preexistent TC Megi are all simulated three runs of five those initiated at 6-10 Aug (more than 10 days before TC Aere's genesis).