Climate modulation of North Atlantic hurricane tracks: observations and implications

In addition to the direct effects of changing the ambient thermodynamic state that tropical cyclones move through, climate variability also relates to hurricane activity through indirect pathways that affect basin-wide circulation patterns. For example, modes of variability such as the Atlantic Meridional Mode (AMM), El Niño / Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), and Madden-Julian Oscillation (MJO) have been shown to affect North Atlantic hurricane activity through changes in atmospheric steering currents and vertical wind shear, among other pathways. These modes affect hurricane genesis location and track, which affect storm duration. This leads to another factor modulating hurricane intensity since storms that last longer also typically achieve greater intensities. Thus hurricane intensity is modulated directly by local ambient thermodynamic conditions and indirectly by broader-scale regional conditions. In addition to the more obvious importance of hurricane tracks as they relate to landfall occurrence, there is then a critical need to better understand the controls of track in order to adequately assess how intensity changes as climate varies.

Here we will present our analysis of North Atlantic tropical storm and hurricane tracks and demonstrate how these tracks are modulated on intra-seasonal to multi-decadal time scales by local and remote climate factors. We will further demonstrate how the addition of track variability can overwhelm the observed trend in the broader regional-mean thermodynamic state, which has the effect of removing the secular trends in the storm-ambient thermodynamic state.