Analysis of the Cause of Rapid Offshore Strengthening of Typhoons Higos and Hato

Using the 6-hourly reanalysis data of the European Center ERA-Interim with horizontal resolution and the hourly typhoon operational data provided by the National Meteorological Center, the circulation situation and intensity structure characteristics of typhoon No. 7 Higos in 2020 and typhoon No. 13 Hato in 2017 are compared and analyzed in this study. The scale of the two typhoons is relatively small. Their generation, moving path, and landing location are relatively similar. In addition, both exhibit rapid offshore strengthening. Comparative analysis results revealed that the common reasons for the rapid offshore strengthening of the two typhoons include the abnormally high sea surface temperature, small vertical shear of wind, and favorable circulation configuration in the upper and lower layers. However, different reasons for the rapid strengthening of offshore waters of the two typhoons are also obvious. The diagnosis and analysis are based on the vertical distribution of potential vorticity, vorticity budget, and vorticity enstrophy. Other factors leading to the rapid growth of typhoon intensity are also obtained.