An Observational Study of Environmental Dynamical Control of Tropical Cyclone Intensity in the Atlantic

An attempt has been made to extend the analysis of environmental dynamical control of tropical cyclone (TC) intensity recently performed for the western North Pacific to the North Atlantic. The results show that both the vertical shear and translational speed have negative effects on TC intensity, consistent with previous findings for other basins. It is shown that few TCs intensified when they moved faster than 15 m s-1. The threshold vertical shear of 20 m s-1 is found above which few TCs intensified and below which most TCs could reach their lifetime peak intensity. The average intensity of total TCs in the Atlantic is a bit smaller than that in the western North Pacific. The SST-determined empirical TC maximum potential intensity (MPI) for 1981-2003 in this study is slightly higher than that found for 1962-1992 by DeMaria and Kaplan in the Atlantic, however.

A new empirical TC MPI has been constructed for the Atlantic. It includes not only the positive contribution by SST but also the combined negative effect of translation and vertical shear as the environmental dynamical control of TC intensity and also the effect of the thermodynamic efficiency. The new empirical MPI not only gives more accurate estimation of real TC MPI but also provides an approximate, explicit measure of the environmental dynamical control of TC maximum intensity. However, the empirical MPI differs considerably from basin to basin. This may reflect the difference in the geographical configuration of the basin and the settings of the large-scale climatological pattern that are not considered explicitly in the empirical MPI. Nevertheless, regardless the basins, the inclusion of dynamical control could improve the estimation of the TC MPI since it provides higher percentage of storms reaching their new MPI than that reaching their SST-determined MPI or the MPI modified to include the thermodynamic efficiency. This implies that the environmental dynamical control could be generally negative to TC intensity.