Scientists renew call for Category 6 hurricane classification: NPR

Residents of Tacloban in the central Philippines in 2013, after Typhoon Haiyan devastated the area. Scientists are renewing the call for a new Category 6 classification for the most powerful hurricanes and typhoons, such as Haiyan.

Aaron Favela/AP

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Aaron Favela/AP

Residents of Tacloban in the central Philippines in 2013, after Typhoon Haiyan devastated the area. Scientists are renewing the call for a new Category 6 classification for the most powerful hurricanes and typhoons, such as Haiyan.

Aaron Favela/AP

Hurricanes are ranked on a scale of one to five, depending on wind speed. The higher the speed, the higher the category. But as climate change makes powerful storms more common, it may be necessary to add a sixth category, according to a new paper published by leading hurricane researchers.

The current five-point scale, called Saffir-Simpson scaleIt was introduced in the 1970s and is used by forecasters around the world including the National Hurricane Center in Florida. Under the scale, storms with maximum sustained winds of 157 mph or higher are classified as Category 5 hurricanes.

Category 5 storms were relatively rare. But climate change is making it more common, research shows. The authors say that some recent Category 5 storms had very high wind speeds, making it logical to classify them as Category 6, if such a category exists.

Authors New paperJames Kossin of the First Street Foundation and Michael Weiner of Lawrence Berkeley National Laboratory have studied the effects of climate change on hurricanes for decades. They propose that Category 5 hurricanes with maximum sustained winds of 157 to 192 mph, and that the new Category 6 should include any storm with wind speeds exceeding 192 mph.

Under the new scale, Category 6 hurricanes would be extremely rare for now. For example, this might apply to the 2013 Typhoon Haiyan that devastated the Philippines with wind speeds reaching around 195 mph. Indeed, scholars in Taiwan at the time argued that Haiyan required a new classification of the category.

Four other storms since 2013 will qualify as Category 6, including 2015's Hurricane Patricia, which struck Mexico, and three hurricanes that formed near the Philippines in 2016, 2020 and 2021.

But other strong storms will not be enough. For example, Hurricane Irma had winds of about 185 mph when it hit the U.S. Virgin Islands in 2018 as a Category 5 storm. Wind damage from Irma led some residents to suggest that the storm should have been rated a Category 6 by forecasters, because they felt they were not adequately warned about the extremely dangerous winds. But under the new proposed scope, Irma would still be a Category 5 hurricane.

The new scale will do little to explain the special danger posed by storms like Hurricane Harvey, Hurricane Florence, or Hurricane Ida, which fit well within the current wind speed scale but caused deadly flooding due to heavy rains. Climate change is to blame – studies have found that hurricanes and other storms drop more rain because a warmer atmosphere can hold more water.

The National Hurricane Center, which handles the official classifications of hurricane categories that threaten the United States and its territories, did not intervene in the issue of adding Category 6. The center has done other things to update hurricane forecasts in response to climate change. However, including new storm surge forecasting tools, and updates that allow forecasters to predict the intensity and location of storms earlier, so people have more time to prepare and evacuate.