Intraseasonal variability and tropical cyclogenesis in the western North Pacific simulated by a global nonhydrostatic atmospheric model

Thirty-one successive daily experiments for extended-range (30 day) forecasts are conducted using a global nonhydrostatic atmospheric model without convective parameterization. The model successfully reproduces tropical cyclogenesis (TCG) in six out of eight cases in the western North Pacific in August 2004, up to 2 weeks prior to cyclone formation. Detailed analyses reveal that Typhoon Songda's genesis is related to the eastward extension of the monsoon trough associated with the intraseasonal variability (ISV). The successful simulation of the migration and extension of the monsoon trough leads to a 2 week forecast for Songda's genesis. These findings highlight the need for a model capable of predicting the modulation of large-scale fields by ISV for TCG forecasts and that a global nonhydrostatic cloud-system-resolving model is a promising tool for TCG forecasts.