New research predicts that North Atlantic hurricane activity will reduce over the next decade and a half, due to the El Nino Southern Oscillation (ENSO) and changes in North Atlantic sea surface temperature. The open ocean is expected to experience the largest decrease, with approximately four fewer tropical cyclones per decade.
Woosuk Choi from Seoul National University in Korea and colleagues used a track-pattern-based tropical cyclone model to examine the role of natural variability and anthropogenic forcing on climate in the near-future – the next one or two decades.
A predicted increase in the frequency of El Niño episodes provides unfavourable conditions for tropical cyclone formation – for example, enhanced vertical wind shear erodes the vertical structure that the storms need to maintain in order to develop. In the North Atlantic, the study shows, the cooling effects of natural variability dominate those of anthropogenic warming. This results in a cooling of the North Atlantic sea surface, which will also suppress tropical cyclone formation.
Many studies focus on cyclone genesis frequency or maximum intensity. But when considering impact, the location of the tracks is most important, as it relates to landfall. Choi and colleagues from the University of California, US, and City University of Hong Kong used a model that divides tropical cyclone tracks into four patterns. They based predictions for each pattern on climate projections from the Climate Forecast System version 2 (CFSv2) in the Coupled Model Intercomparison Project (CMIP), and compared tropical cyclone activity between 2002–2015 and 2016–2030.
Predicting cyclone activity in the near-future is complicated by uncertainties from both internal variability (natural oscillations) and external forcings such as greenhouse gases. The timescale lies between short-term predictions and long-term climate change, where in each case only one of the uncertainties dominates. Predictions in the near-future, however, are vitally important for planning mitigation strategies for extreme weather such as hurricanes.