Hurricane Milton, which has been gaining strength since the beginning of the week, may rewrite history. According to the President of the United States, Joe Biden, it could be the worst hurricane in a hundred years. How are hurricanes classified and why is the sixth, as yet non-existent degree, being added? We bring you a short overview of the classification of hurricanes according to the so-called Saffir-Simpson hurricane scale.
Photo: Reuters, NASA
Hurricane Florence as seen from the ISS.
First of all, it is necessary to explain what hurricanes are and how they form. Hurricanes are tropical cyclones that form over warm oceans. They most often occur in early summer, but they can form as late as November when the oceans are still warm enough. In order for a hurricane to form, several conditions must be met – the water temperature must reach at least 26.5 °C at a depth of at least 50-70 meters.
The high temperature of the ocean and plenty of sunlight cause water to evaporate. Rising warm air rich in water vapor cools in the upper atmosphere, causing the water vapor to condense and form clouds. This process releases a large amount of heat, which further promotes the upward movement of air.
Another condition for the formation of a hurricane is a large grouping of storm clouds, which leads to a decrease in air pressure near the ground. Subsequently, a centripetal wind is created, which rotates counterclockwise in the northern and clockwise in the southern hemisphere due to the Coriolis force. This spinning wind forms a cyclone, which can reach speeds of up to 120 kilometers per hour. When the wind speed exceeds this limit, we speak of a hurricane.
Saffir-Simpson scale
A pair of scientists – engineer Herbert Saffir and meteorologist Robert Simpson – worked on the definition of what already is and what cannot yet be considered a hurricane in the 1970s. During his work for the United Nations, Saffir created a simple system for classifying windstorms according to wind speed and their potential impact on the environment. Simpson, who worked at the US National Hurricane Center, then expanded Saffir’s definition to include several other variables, such as the pressure at the center of the hurricane and the level of tidal waves. This is how the Saffir-Simpson scale was created, which divided hurricanes into five categories. The boundaries of the categories are determined by the wind speed.
Category 1: 119–153 km/h
- Wind speed: 119 to 153 km/h
- Pressure: ≥ 980 hPa
- Height of tidal waves: 1,2 – 1,5 metra
- Damage: Damage to low-quality structures, breaking tree branches. Flooding of coastal areas and minor flooding in low-lying areas is also possible.
Category 2: 154–177 km/h
- Wind speed: 154 to 177 km/h
- Pressure: 965 – 979 hPa
- Height of tidal waves: 1,8 – 2,4 metra
- Damage: Significant damage to roofs and windows, some poorly fixed structures may be blown away. Coastal areas may be flooded, there is a risk of power outages lasting several days.
Category 3: 178–208 km/h
- Wind speed: 178 to 208 km/h
- Pressure: 945 – 964 hPa
- Height of tidal waves: 2,7 – 3,7 metra
- Damage: Houses can be severely damaged or destroyed, roofs and windows of buildings are often destroyed. Significant flooding of coastal areas, with low-lying areas potentially under water.
Category 4: 209–251 km/h
- Wind speed: 209 to 251 km/h
- Pressure: 920 – 944 hPa
- Height of tidal waves: 4,0 – 5,5 metra
- Damage: Significant damage to the destruction of buildings, blowing off roofs and parts of buildings. Coastal areas are subject to extreme flooding, with large sections potentially uninhabitable for extended periods of time. Power outages can last for weeks to months.
Category 5: over 252 km/h
- Wind speed: At 252 km/h
- Pressure: < 920 hPa
- Height of tidal waves: Over 5.5 meters
- Damage: Large parts of buildings can be completely destroyed. Dense vegetation is destroyed, areas can be uninhabitable for months. Huge tidal waves cause massive flooding that can reach deep inland and destroy coastal infrastructure and ecosystems.
In connection with Hurricane Milton, there is also public talk about changes in the classification of hurricanes and the addition of a sixth category. Some experts believe that adjustments in the classification should occur mainly due to climate change, which has an impact on the more frequent occurrence of strong hurricanes. According to the National Hurricane Center (NCH), Hurricane Milton already reached wind speeds of 270 kilometers per hour on Tuesday afternoon. In recent years, there have been several hurricanes whose intensity was so high that they far exceeded the wind speed of the fifth category. Although there is no upper limit to this category, some experts are calling for changes to the classification to help better differentiate hurricanes’ destructive potential. However, the American NCH issued a statement in February of this year, according to which it does not plan to add a sixth category, as it could be confusing. However, this may change depending on the damage caused by Hurricane Milton, which may be the worst in a hundred years.
Source: vat.pravda.sk
