EXPERT REACTION: Faster tropical cyclones in a warming world

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In some parts of the world, a Category 5 hurricane signifies the most extreme wind speeds starting at 252 km/h. New research looks into why creating a new Category 6 could help capture just how much more intense the biggest tropical cyclones are expected to become under climate change. Warm tropical waters are a key ingredient for a tropical cyclone to form, and even warmer waters mean there’s more energy available to feed into them. The authors explore how a new Category 6 for the Saffir-Simpson scale that starts at 309 km/h could help illustrate this change. Five storms in the past nine years would have qualified as a Category 6, they found.

Journal/conference: PNAS

Link to research (DOI): 10.1073/pnas.2308901121

Organisation/s: Lawrence Berkeley National Laboratory, US; First Street Foundation, USA; University of Wisconsin-Madison, USA

Funder: M.F.W. was supported by the Director, Office of Science, Office of Biological and Environmental Research of the U.S. Department of Energy under Contract No. DE340AC02-05CH11231 under the Regional and Global Model Analysis program.

Media release

From: PNAS

Saffir-Simpson hurricane scale in a warming world

Researchers introduce an extension of the Saffir-Simpson hurricane wind scale to include a Category 6. Since the early 1970s, the National Hurricane Center has communicated the risk of damage from hurricanes using the Saffir-Simpson hurricane wind scale. The scale labels hurricanes as Category 1 through 5, with Category 5 indicating any hurricane with windspeeds of 70 m/s or greater. Michael F. Wehner and James P. Kossin examined extremes in hurricane wind speeds to determine whether the open-ended Category 5 is sufficient to communicate risk in a warming climate. An increase in ocean temperatures provides additional heat energy for hurricane intensification, the authors note. The authors introduced a hypothetical Category 6, which would encompass storms with wind speeds greater than 86 m/s. Analysis of historical data from 1980 to 2021 showed five storms that would have been classified as Category 6, all of which occurred in the past 9 years of the record. Reanalysis and climate modeling suggested that the risk of Category 6 storms increases by 50% near the Philippines and doubles in the Gulf of Mexico with 2 °C of global warming above pre-industrial levels. According to the authors, appending the Saffir-Simpson hurricane wind scale may raise awareness of the intensification of hurricanes and other tropical cyclones in a warming climate.

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