Tropical Cyclone Rapid Intensification & it’s Impact for (Re)insurers

The rapid intensification (RI) of tropical cyclones (whereby the maximum sustained wind increases by 30 kt (15.4 m s−1) or over in a 24-period) has garnered particular attention in recent years, with insurers and risk managers increasingly concerned that warmer ocean basins are fuelling increasingly intense landfalling hurricanes (Kaplan et al 2010).RI was a notable characteristic of both Hurricanes Helene and Milton during the 2024 North Atlantic Hurricane Season. These two storms caused 78bn and 35bn in economic losses respectively (Gallagher Re), with Helene undergoing explosive RI of 55mph in the 24-hours ahead of landfall, increasing its windspeed upon impacting the Florida coast to 140mph, classifying it as a category 4 storm (Saffir-Simpson scale).In this study, key trends have been analysed in the pattern of RI of Tropical Cyclones globally over the period 1990-2023, including the response of different ocean basins as well as the critical impact of teleconnection patterns such as the El Nino Southern Oscillation (ENSO) in modulating the geographic dispersion of intensifying cyclones. The study shows that while most Tropical Cyclones (>90%) in recent decades have exhibited some form of RI in their development prior to landfall, there is a clear upward trend in recent years in some ocean basins towards a pattern of so-called ‘Explosive’ Rapid Intensification (whereby a storm intensifies at a rate >50 kt in 24 hours).With the most extreme Tropical Cyclones undergoing explosive RI and potentially landfalling with greater intensity than in previous decades, this research studies the potential economic and (re)insured loss implications for global risk management. Particular focus is given to the North Atlantic as well as the strong signal of RI occurrence changes under ENSO and over the study period in the North-West and Eastern Pacific basins.Kaplan, J., DeMaria, M., & Knaff, J. A. (2010). A revised tropical cyclone rapid intensification index for the Atlantic and eastern North Pacific basins. Weather and forecasting, 25(1), 220-241.