On the Calculation of Vertical Shear: An Operational Perspective

Many studies have shown an inverse relationship between vertical shear and intensity. Indeed, tropical cyclones are quite sensitive to the magnitude of shear with past studies citing a “critical shear” threshold beyond which weakening or arrested development occurs. However, the commonly used vector subtraction between two single levels, usually 850 and 200 hPa, may not always fully resolve vertical shear. Since the current operational Statistical Hurricane Intensity Prediction Scheme (SHIPS) model utilizes the 850 and 200 hPa levels in its shear calculations, individual runs may be improved by using an alternative means for calculating shear. This study evaluates the sensitivity of the SHIPS models to varying the levels used in the calculation of vertical shear in order to determine if alternative methods provide better results.