Influence of Large-Scale Environment on the Size of Secondary Eyewalls

Secondary eyewalls (SEs) are frequently observed in intense tropical cyclones. The separation distance between the primary eyewall and the SE can range from more than one hundred to less than ten kilometer. It is generally suggested that internal dynamic structures of tropical cyclone determine the radiual location of the SE. In this study, the potential role of large-scale environment is investigated using NCEP/NCAR reanalysis data. It is found that the environmental middle-level relative humidity, surface pressure, horizontal wind vertical shear, the potential maximum intensity (MPI) and the storm latitude and intensity can all used as predictors for the formation location of the SEs. A prediction scheme is established by using a multiple linear regression model to provide up to 48 hr guidance for the radial location of SEs formation. The prediction scheme explains about 40% of the variance of the radial locations of the SE formation. The physical interpretation of the predictors is also provided.