A first look at the genesis of Typhoon Manyi (2007) during the TCS-08 Dry Run

As part of the ONR-sponsored TCS-08 “Dry Run” based at the Naval Postgraduate School at Monterey, we simulated the formation of Manyi, a super typhoon over the western North Pacific in July 2007, using the Weather Research and Forecasting (WRF) model. GFS analysis and TRMM precipitation data suggest that the formation of Manyi was associated with a quasi-stationary monsoon disturbance and a westward-propagating equatorial Rossby wave. The genesis of Manyi was preceded by a superposition of these two disturbances. The WRF simulation shows that a closed circulation in the “wave gauge” frame of reference (moving at a constant zonal velocity set by the equatorial Rossby wave) served as the “sweet spot” of the synoptic-scale disturbances and later developed into a storm vortex at 12Z 07 July. The numerical simulation predicts a spin up of the mesoscale vortex by the low-level convergence associated with multiple vortical hot towers. The model simulation and diagnosis indicates a “bottom up” development process and moreover suggests that a “wave gauge” frame of reference is an appropriate choice for understanding the evolution of proto-vortices embedded within the mother wave.