Numerical Simulations of the Genesis of Typhoon Nuri (2008) during TCS08/TPARC: Sensitivity to Initial Conditions and Implications for the Roles of Environmental Conditions

Sensitivity of numerical simulations of the genesis of Typhoon Nuri (2008) to initial conditions is examined with an advanced research version of the Weather Research and Forecasting model. Two sets of experiments are conducted using initial and boundary conditions derived from two different global analyses. Results indicate that one set of numerical simulations fails to predict Nuri's genesis. The other set successfully captures the processes of Nuri's genesis and early intensification, as it produces stronger cyclonic circulation, upward vertical velocity, and a stronger gradient of vertical velocity, which leads to more rapid development of low-level vorticity. Differences between the two initial conditions and simulations are diagnosed to understand the environmental factors that influence Nuri's genesis. Despite warm SSTs and low vertical wind shear, favorable conditions for Nuri's genesis are provided by the strong and well-organized mid-level vortex, strong vertical motions of the upward vertical mass flux with a bottom-heavy profile, and low to mid-level moisture. Prior to the genesis of Nuri, the formation of a low- to mid-level cold pool enhances the low-level updraft by a bottom-heavy mass flux profile along with the development of a low-level vortex inflow. An additional set of sensitivity experiments indicates that initial moisture conditions play a significant role in Nuri's genesis. Specifically, enhancement of mid-level moisture is favorable for convection and vortex development.