A Sensitivity Study on the Initial Field for the Track and Heavy Precipitation Forecast of Typhoon Haikui(2012)after Entering the Saddle Field

LIU Qiao; QIU Xuexing; ZHU Hongfang; AN Jingjing; WANG Dongyong; WANG Gen

doi:10.16032/j.issn.1004-4965.2026.003

Abstract：Typhoon Haikui(2012)was influenced by a saddle-point flow field,resulting in nearly stationary movement in southern Anhui and causing extreme rainfall.To examine the sensitivity of the track and precipitation forecast of Haikui to the model's initial conditions after entering the saddle-point region,ensemble forecast experiments and sensitivity experiments were conducted for Haikui using the Weather Research&Forecasting(WRF)model coupled with an Ensemble Kalman Filter(EnKF)assimilation system.The results show that:(1)After Typhoon Haikui made landfall in Zhejiang and moved northwestward into Anhui,typhoon tracks forecast by ensemble forecasting experiments can mainly be divided into the stagnation type,the eastward-turning type,and the westward-moving type.The stagnation tracks are most similar to the observed track of Haikui.(2)Compared with the circulation of the typhoon itself,differences in the environmental field of initial conditions are the key factor causing variations in typhoon motion in the experiments.The typhoon's movement is more sensitive to the continental high-pressure system and mid-latitude trough in the northwestern part of the simulation domain.(3)When the intensities of the continental high and trough are comparable in the initial field,the weakened typhoon circulation remains between the continental high and the subtropical high,leading to stagnation over southern Anhui.This,combined with cold air interaction,results in heavy rainfall in southern Anhui and northern Jiangxi.When the continental high is weak and the trough is strong in the initial field,the typhoon is forecasted to be in a saddle-point field in the 24-hour forecast.However,both the continental high and the subtropical high are relatively weak.As the trough moves southward,the continental high weakens and retreats westard,and the subtropical high shifts eastward.The typhoon then turns northeastward,resulting in heavy rainfall in Jiangsu.Conversely,when the continental high is strong but the trough is weak,the typhoon continues moving westward.The influence of the trough and cold air shifts to the north.Cold air is blocked by the high pressure and fails to directly interact with the typhoon's circulation,resulting in relatively weaker precipitation in southern Anhui.