A Statistical Analysis on the Dependence of Tropical Cyclone Intensification Rate on the Storm Intensity and Size in the North Atlantic

The dependence of tropical cyclone (TC) intensification rate IR on storm intensity and size was statistically analyzed for North Atlantic TCs during 1988-2012. The results show that IR is positively (negatively) correlated with storm intensity (the maximum sustained near-surface wind speed V-max) when V-max is below (above) 70-80 knots (kt; 1 kt = 0.51 m s(-1)), and negatively correlated with storm size in terms of the radius of maximum wind (RMW), the average radius of gale-force wind (AR34), and the outer-core wind skirt parameter DR34 (=AR34 - RMW). The turning point for V-max of 70-80 kt is explained as a balance between the potential intensification and the maximum potential intensity (MPI). The highest IR occurs for V-max = 80 kt, RMW <= 40 km, and AR34 = DR34 = 150 km. The high frequency of occurrence of intensifying TCs occurs for V-max <= 80 kt and RMW between 20 and 60 km, AR34 <= 200 km, and DR34 <= 150 km. Rapid intensification (RI) often occurs in a relatively narrow parameter space in storm intensity and both inner- and outer-core sizes. In addition, a theoretical basis for the intensity dependency has also been provided based on a previously constructed simplified dynamical system for TC intensity prediction.