Atlantic hurricane activity has been recorded for more than 170 years, but understanding its trends requires separating real changes in the storms from changes in our ability to observe them.
What a "Normal" Season Looks Like
Based on the 1991–2020 climatological average, a typical Atlantic season produces about 14 named storms, 7 of which become hurricanes and 3 of which reach major-hurricane status (Category 3 or higher).1 Individual seasons vary enormously, from quiet years with a handful of storms to hyperactive years such as 2005 and 2020, which each produced roughly 30 named storms.
Natural Cycles: The AMO and ENSO
Atlantic activity swings on both multi-decadal and year-to-year cycles. The Atlantic Multidecadal Oscillation (AMO), a 60–80-year cycle in North Atlantic sea surface temperatures, modulates long stretches of higher or lower activity, and the period from 1995 onward has been notably active.1 On shorter timescales, the El Niño–Southern Oscillation (ENSO) strongly shapes each season: El Niño tends to increase wind shear over the Atlantic and suppress hurricanes, while La Niña tends to favor them.
The Observation Problem
Comparing modern seasons to the distant past is fraught, because detection has improved dramatically. Before the satellite era (pre-1966), storms that stayed at sea or struck sparsely populated areas were often missed, and weak systems were undercounted.2 Apparent increases in storm counts therefore partly reflect better observation rather than more storms, a bias researchers must correct for before drawing conclusions about long-term frequency.2
Climate Change Signals
Once these factors are accounted for, the clearest climate-change signals are in intensity and rainfall, not overall frequency. The IPCC's Sixth Assessment Report concludes it is likely that the global proportion of intense (Category 4–5) tropical cyclones has increased, and very likely that tropical-cyclone rainfall rates will rise with warming.3 Satellite analyses likewise find that the proportion of storms reaching major-hurricane intensity has grown over recent decades.4 Global tropical-cyclone frequency, by contrast, is not projected to change greatly, and trends in total counts remain uncertain.3
Rapid Intensification on the Rise
One of the most consequential trends is in rapid intensification: an increase of at least 35 mph (55 km/h; 30 kt) in a storm's maximum winds within 24 hours. Bhatia and colleagues (2019) found a significant upward shift in Atlantic intensification rates between 1982 and 2009, with the fastest-strengthening storms strengthening faster than in the past.5 Rapid intensification is especially dangerous near land, because a storm can leap one or two Saffir-Simpson categories in the final day before landfall, as Michael (2018), Ida (2021), and Ian (2022) all did, leaving little time to revise warnings or evacuate.
Slower, Wetter Storms
Intensity is not the only thing changing. Kossin (2018) documented a roughly 10 percent global slowdown in the forward (translation) speed of tropical cyclones over the past 70 years.6 A slower storm lingers longer over any given location, multiplying the hours of wind and, critically, the total rainfall it dumps, a major factor in the catastrophic inland flooding of Hurricane Harvey (2017), which stalled over Texas for days. Rising sea levels compound the threat from the coast: every inch of global sea-level rise lifts the baseline on which a hurricane's storm surge is stacked, so the same surge reaches farther inland than it would have a century ago.3
Reading a Single Season
Any single busy or quiet season carries less signal than the headlines suggest. Atlantic activity blends long natural cycles, year-to-year ENSO swings, an evolving observing system, and a warming climate that is making the strongest storms stronger and wetter, and pulling those threads apart is what separates a real trend from a noisy year.3 In our own view the intensity and rainfall signals are the ones worth watching, because they are where the physics and the observations agree most clearly; the frequency question remains genuinely unsettled, and we would be cautious of anyone who states it as decided. For how these trends translate into damage and dollars, see climate change and hurricane intensity and costliest natural disasters.
Sources
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National Hurricane Center. Tropical Cyclone Climatology. NOAA. https://www.nhc.noaa.gov/climo/ ↩ ↩2
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Landsea, C. W., & Franklin, J. L. (2013). Atlantic hurricane database uncertainty and presentation of a new database format. Monthly Weather Review, 141(10), 3576–3592. https://doi.org/10.1175/MWR-D-12-00254.1 ↩ ↩2
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Seneviratne, S. I., et al. (2021). Weather and climate extreme events in a changing climate. In Climate Change 2021: The Physical Science Basis (IPCC AR6 WG1, Ch. 11). Cambridge University Press. https://www.ipcc.ch/report/ar6/wg1/ ↩ ↩2 ↩3 ↩4
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Kossin, J. P., Knapp, K. R., Olander, T. L., & Velden, C. S. (2020). Global increase in major tropical cyclone exceedance probability over the past four decades. Proceedings of the National Academy of Sciences, 117(22), 11975–11980. https://doi.org/10.1073/pnas.1920849117 ↩
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Bhatia, K. T., Vecchi, G. A., Knutson, T. R., et al. (2019). Recent increases in tropical cyclone intensification rates. Nature Communications, 10, 635. https://doi.org/10.1038/s41467-019-08471-z ↩
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Kossin, J. P. (2018). A global slowdown of tropical-cyclone translation speed. Nature, 558, 104–107. https://doi.org/10.1038/s41586-018-0158-3 ↩