Should We Add Category 6 to the Hurricane Scale? Experts Weigh In

For more than half a century, the Saffir-Simpson Hurricane Wind Scale (SSHWS) has defined hurricane intensity by the maximum sustained wind speed, classifying storms into categories from 1 to 5. Until 2012, the SSHWS also took into account the central storm pressure and storm surge, but these factors were later removed to avoid unnecessary confusion among the public. Climate change is expanding risk zones not only from wind strength but also due to storm surge, flooding, and precipitation. Several ultra-strong storms, such as Milton, Patricia, and Typhoon Haiyan, have raised questions: is it time to add Category 6? In this article we examine various expert viewpoints on the advisability of introducing Category 6 or a possible reorientation of the classification concept.

Some scientists support a multi-factor approach that accounts not only for wind, but also for storm surge and precipitation. Others believe that the modern system can remain effective if risk explanations are made clearer in the context of global warming, without adding a new category.

Key expert positions regarding the possibility of Category 6

“In my view, Category 6 is unnecessary. Category 5 of this scale already signifies a completely devastating impact. There were discussions in the scientific community about ten years ago, and the overall conclusion was: it’s better to create another system. Our new scale, Tropical Cyclone Severity Scale (TCSS), accounts for three main hazards – wind, storm surge, and precipitation – each rated from 1 to 5. The overall category corresponds to the highest of these hazards. For example, Hurricane Florence in 2018 would have Category 1 for wind, Category 4 for storm surge, and Category 5 for precipitation, so the overall category would be Category 5. If you consider floods and human losses, someone who survived it would agree that calling it Category 1 does not reflect the real risk. TCSS also shows a high risk when two or more hazards are present: if at least two hazards are high, the overall category increases. Thus tropical cyclones rated 3 for wind and surge, but 1 for precipitation, would be classified as Category 4. In two scenarios a high-risk cyclone could receive Category 6 under TCSS: if two hazards are Category 5, or two are Category 4 and one is Category 5. This should warn people about a hurricane with several extraordinary hazards.”

According to Brian McNoldy, introducing Category 6 is not necessary and will not add new value to the existing messaging system. Since 1980, Category 5 hurricanes account for about 5% of named storms worldwide, and in the Atlantic about 4%. There are no compelling advantages to dividing this small number of storms into even smaller categories. The most powerful Atlantic hurricane on record remains Allen (1980) with a maximum sustained wind of 190 mph; since then no similar figures have been recorded. If the threshold for Category 6 is at least 193 mph – as some research suggests – no Atlantic hurricane today would qualify. Moreover, dividing such excessive data into even smaller categories does not change risk communication. The National Hurricane Center describes landfall of a Category 5 hurricane as “catastrophic” – a significant portion of frame houses will be destroyed, roofs will fail, power lines will go down, leading to a prolonged power outage. An additional signal of Category 6 at landfall could overemphasize risks – other hazards remain important.”

“SSHWS was developed in the United States to reflect the maximum sustained wind and the associated level of destruction. If a storm reaches Category 5, catastrophic consequences are expected. Therefore creating a new Category 6 makes no sense from a threat communication standpoint.”

Liz Ritchie-Tyo emphasizes that an important multi-factor classification can help predict risks depending on where the storm lands: coastal areas need an emphasis on winds, waves, and storm surge, while inland regions – on floods and landslides. Maximum wind speed does not always correlate with rainfall intensity, so a system that accounts for multiple hazards may more accurately reflect different risks and their impact on people and infrastructure.

“At present, the National Hurricane Center does not plan to change SSHWS or add Category 6. Classification systems in all tropical basins are based on maximum wind speed. Even if a storm strengthens, damage may not become worse than ‘catastrophic’. The main limitation of existing systems is not that they fail to cover a high enough level, but that they focus solely on the wind threshold and do not account for other hazards. A multi-hazard system is needed to convey risk from multiple hazards: wind, storm surge, precipitation, floods, and landslides. Results depend on the landfall location: the coast requires more attention to winds and storm surge, further inland – to floods and landslides. Also, maximum wind speed does not always correlate with rainfall intensity.”

“There are currently no plans to change SSHWS or to introduce Category 6. The tropical-basin classification systems are based on maximum wind speed. Even with storm intensification, damage does not necessarily exceed the ‘catastrophic’ threshold. The main limitation of existing systems is their focus on the wind threshold without considering other hazards. A multi-hazard system is needed to convey risk from multiple hazards: wind, storm surge, precipitation, floods, and landslides. Results depend on landfall location: the coast requires greater attention to winds and storm surge, further inland – to floods and landslides. Also, maximum wind speed does not always correlate with rainfall intensity.”

In conclusion, experts agree that a simple additional Category 6 is not a universal solution for all scenarios. The main need is clearer and more multifaceted informing of the public about the risks, as well as improved forecasting and warning tools, including storm-surge maps and inland-flood maps. A modern system, complemented with detailed messages about different hazards and their local impacts, can provide a more appropriate public response to emergencies than reducing all risks to a single category.