Abstract:In contrast to the observation, there was an obvious deviation in tack and rainfall distributions in operational Typhoon Kujira (1508) forecasting in Hainan. It brought a great challenge to the operational typhoon warning service in Hainan. In this paper, the reasons of the track and rainfall forecast deviations for Typhoon Kujira are investigated by using conventional observation data, FY-2G satellite data and ECMWF ERA interim reanalysis data (0.25°×0.25°) and operational deterministic model products. Meanwhile, the reason of the reverse rainfall distributions, which was caused by two groups of tropical cyclones in summer with the similar tracks to Typhoon Kujira, is analyzed. The results show that (1) the larger deviation in operational positioning of Typhoon Kujira for its weak intensity, and a weaker and more eastward located subtropical high predicted by ECWMF are the main reasons for the failure of Typhoon Kujira’s track and landing point forecastings. (2) An enhanced subtropical westerly jet and upper-level north-easterly over South China Sea are well forecasted by ECMWF. However their roles in typhonic unsymmetrical structure via strong vertical shear are neglected, thus leading to the forecast deviation of Typhoon Kujira (1508) in track and rainfall distributions. (3) The evolution of the subtropical westerly jet and upper tropospheric westerly trough should be paid more attention in operational typhoon track and rainfall forecastings. When the subtropical westerly jet intensifies and moves southeastward, the vertical wind shear becomes greater accompanying the accelerating of upper-level northeasterly near the typhonic center. Severe convection tends to develop in the south side of the typhoon, which facilitates a westward moving of typhoon with heavy rainfall occurring at the left side of its track. However when the westerly trough moves southeastward in the vicinity to the typhoon circulation, the vertical wind shear near the typhonic center weakens significantly. At this time, the convection tends to develop in the north side of typhoon, which leads to a northward moving of typhoon with heavy rainfall occurring at the right side of its track.