Abstract/Summary

Understanding which environmental processes are responsible for driving the interannual and decadal variability of tropical cyclones (TCs) is important for providing TC impact-related mitigation and planning information to the responsible agencies and business. TC activity in the northern hemisphere is examined in IBTrACS, seven recent reanalyses and coupled and atmosphere-only simulations at various resolutions from HadGEM3-GC3.1. Drivers of TC activity are examined for the current climate, on decadal time scales and in scenarios of a warming climate. Different tools, including the standard power spectrum method, the wavelets, and the Empirical Teleconnections method are utilized. TC activity in the North Atlantic (NATL), characterized by high variability, is primarily influenced on interannual and decadal time scales by the Atlantic Multi-decadal Oscillation (AMO) via warm local Sea Surface Temperatures (SSTs). The primary driver for TC activity in the Eastern Pacific (EPAC) and Central Pacific (CPAC) regions under current climate conditions is the El-Niño Southern Oscillation (ENSO) with associated warm SSTs and weak Vertical Wind Shear (VWS) in the Pacific, whereas decadal variability is driven by both ENSO and AMO. Typhoon activity in the Western Pacific (WPAC) is found to be driven by more than one main driver in observations and the model. Variability of TC activity in the North Indian Ocean (NIND) is not linked significantly to the climate modes (ENSO, AMO, PDO) examined in the study. With a warming climate, ACE increases in NATL, EPAC, CPAC and WPAC and decreases for NIND. For EPAC there is a westward shift, while for WPAC there is a poleward shift in TC activity. Finally, a simple, open-source hurricane-catastrophe model is developed for assessing risk associated with hurricane winds for Bermuda and it is used to test the sensitivity of hurricane wind risk to variability of the frequency of events, particularly related to the AMO.