Effects of Typhoon Fitow residual circulation on the relationship between surface wind field and precipitation in Shanghai

Heavy precipitation, triggered by the residual circulation from Typhoon Fitow (2013), struck Shanghai with a spatial inhomogeneity distribution. Using multi-physical diagnostic analysis based on automatic weather stations (AWS) observations, the fifth-generation ECMWF re-analyses (ERA5), FY satellite products, and typhoon track data, this study investigates the relationship between the surface wind field and precipitation in Shanghai. The main results are as follows: (1) The Shanghai Central Area (SCA) decelerated the eastward progression of the northerly wind associated with the typhoon’s residual circulation. The low-wind area and wind deflection around the SCA enhanced the wind field convergences in its surrounding regions. (2) The slow-moving convective systems prolonged the duration of rainfall, while the wind deflection around the SCA further strengthened surface wind convergence conditions. (3) Intense surface Q vector convergence persisted between the northerly wind from the residual circulation and the northeasterly maritime wind. Precipitation attenuated rapidly within 2 h following the weakening of the Q vector convergence, suggesting that this parameter served as a reliable indicator for the development of the studied precipitation event. Additionally, surface water vapor advection was channeled by wind deflection around the SCA, leading to water vapor accumulation in both upwind and downwind areas of the SCA.