A forecast sensitivity study on the intensity change of Typhoon Sinlaku (2008)

Typhoon Sinlaku (2008), one of the super typhoons in the western North Pacific in 2008, had two distinct periods of rapid intensification (RI). Using the newly developed Weather Research and Forecasting adjoint modeling system, the forecast sensitivity to the initial conditions during Sinlaku's first RI was investigated. The highly sensitive region influencing the intensity change during RI of Sinlaku was found to be located over the storm core region and its vicinity. The forecast sensitivity signatures occurred in almost all vertical levels. The storm intensity was found to be most sensitive to low-level initial moisture, indicating the accurate initialization of moisture near the initial storm center and that its vicinity plays a crucial role in subsequent intensity forecasts. The targeted experiment based on the adjoint-derived sensitivities further verified that the assimilation of moisture observations near the storm core region had a remarkable impact on the forecast of rapid intensification of the Sinlaku (2008). These results highlight the potential value of adjoint method in the targeted observations in tropical cyclones' intensity forecasts.