台风鲸鱼(1508)路径和降水业务预报偏差原因分析

摘要

1508号台风鲸鱼路径和降水业务预报均出现明显偏差,造成该台风预报服务效果很差.本文主要利用常规观测资料、卫星资料、EC模式预报结果和ERA-interim再分析资料(0.25°×0.25°),探讨“鲸鱼”路径和降水业务预报偏差的原因,同时对比分析与“鲸鱼”路径相似的两组夏季台风出现近乎反向的强降水落区的成因.结果表明:(1)“鲸鱼”强度偏弱,业务定位出现较大偏差,同时EC模式对副热带高压预报明显偏弱偏东,是其路径及登陆点预报偏差的主要原因.(2)EC模式较好地预报出副热带西风急流加强、南海海域高层东北风加大的过程,但业务中却忽视了它们通过加强环境风垂直切变对台风非对称结构的作用,从而导致“鲸鱼”路径和降水预报出现偏差.(3)台风路径和降水预报要特别关注副热带西风急流和对流层高层西风槽的演变,副热带西风急流加强东进南落,台风中心附近高层东北风加大,环境风垂直切变随之加大,其南侧对流发展旺盛,台风移动路径偏西分量加大,强降水主要位于其路径左侧;西风槽东移南压,且与台风环流靠近,台风中心附近环境风垂直切变明显减小,其北侧对流发展旺盛,台风移动路径偏北分量加大,强降水主要位于其路径右侧.%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 EC-MWF 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 northeasterly 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.