Several scientists propose adding a sixth category to the hurricane intensity scale. Due to the increase in sea water temperature, the risk of a hurricane with winds over 300 km/h is now very high.
The intensity of hurricanes is classified according to the Saffir-Simpson scale developed in 1969 by the civil engineer Herbert Saffir and the meteorologist Robert Simpson, director of the National Hurricane Center (Florida) at that time: from category 1 (119 to 153km/h) to category 5 (more than 251km/h). The formation and strength of a hurricane depends on five factors, namely the sea temperature which must exceed 26,5°C to a depth of at least 60m, with a surface water temperature reaching or exceeding 28 to 29°C. Hot water, a source of energy for cyclonic phenomena, intensifies winds and rain. In 2023, water temperatures will reach a record high, particularly in the North Atlantic, the basin of hurricanes that hit the Antilles and the United States. For one of the developers of the intensity scale, Robert Simpson, there is no sufficient reason to include category 6 because a hurricane wind exceeding 251 km/h would in any case cause considerable damage. The National Hurricane Center (NHC) has also clarified that the addition of a sixth category is not on the agenda for the moment. Conversely, other scientists consider that this new category would nevertheless make it possible to characterize hurricanes with winds greater than 308 km/h. According to scientists from the Lawrence Berkeley National Laboratory (California), five hurricanes could already have been classified in category 6 between 1980 (start of taking measurements) and 2021, all having occurred from 2012 including Irma in 2017 with gusts of 360km/h.
In an environmental context of global warming, the number of hurricanes generating winds over 308 km/h will only increase. With global warming already active at +1,5°C, the number of category 6 hurricanes will increase by 50% near the Philippines and in the Gulf of Mexico according to the study published in Proceedings of the National Academy of Sciences. As a reminder, the Saffir-Simpson scale is only used to communicate the risk linked to winds. Other hazards from hurricanes, such as precipitation, flooding, and storm surge, are reported by the NHC through specialized measurements. _VX
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