Interactions between Super Typhoon Megi (2010) and the Monsoon Gyre

Abstract:

Accurate prediction of tropical cyclone track is critical for high-impact weather preparedness, especially as the storm is near the coastal region. The track prediction for super typhoon Megi (2010) in the western Pacific was notoriously bad as most operational models predicated a mainly westward movement while Megi actually made a northward turning after it has crossed the Philippines islands. In this study, we try to understand this rather irregular motion for Megi. Examination of NCEP reanalyzed fields indicated that during this period a low-frequency (10-60-day) monsoon gyre in the vicinity of Megi may have interactions with the latter. To understand the effect of the low-frequency mode on the movement of Megi, numerical experiments were designed and conducted. The total flow from the analyzed field is separated into 1) a slowly varying background state, 2) a 10-60-day low frequency component representing the monsoon gyre, and 3) a 10-day high-pass filtered component representing Megi. In the control experiment, the total field containing all three components is used as the initial and lateral boundary conditions, and the WRF model is able to simulate Megi’s sharp northward turning successfully. In the second experiment, the 10-60-day mode is removed from the initial and lateral boundary fields. In the absence of the low-frequency mode, Megi moves westward and only slightly northwestward without turning north. When the vortex representing Megi was removed, the movement of the monsoon gyre was also affected. These experiments indicated strong interactions between Megi and the monsoon gyre. The interactions and the way the monsoon gyre actually affected the track of Megi will be discussed in the presentation.