An objective method for discriminating the process of extratropical transition (ET) in tropical cyclones is introduced. With this method, the gridpoint output data of NWP are used to calculate three parameters: storm-relative thickness symmetry (B), low-level ( flV TL) and upper-level thermal wind ( flV TU). This objective method is easy to calculate and convenient for operational use. To verify the method, this paper uses the NCEP reanalysis data to identify the evolution of ET for"Haima", a tropical storm (0421) that affected the eastern part of China in 2004. The result shows that the three parameters defined with the objective method are good indicators of the ET process.
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