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Origins -

The classification of hurricanes can be traced back to the mid-20th century. In the hope of understanding the destructive nature of storms, early meteorologists sought ways to differentiate them based on intensity. This led to the development of a structured categorization system.

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Initial storms -

Before formal categorization, storms were identified primarily by their region and date. There was no standard system, but early weather scientists began recording pressure, wind speeds, and damage.

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The 1900 Galveston hurricane -

The Great Galveston hurricane remains one of the deadliest natural disasters in US history. It killed up to 12,000 people and caused the modern equivalent of US$1.25 billion in damage. The hurricane’s devastation highlighted the need for better storm warnings and classifications.

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The Saffir-Simpson Scale -

In 1971, civil engineer Herbert Saffir and meteorologist Robert Simpson developed the Saffir-Simpson Hurricane Wind Scale (SSHWS). This scale categorized hurricanes based on wind speed, which was considered the most measurable aspect correlating to damage.

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Wind speed -

Wind speed was chosen as the primary metric for hurricane classification because it directly correlates with potential destruction. It is easier to measure wind speed consistently across regions, which provides a universal language to describe storm intensity.

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Measurement -

Wind speed and wind pressure are both measured using an instrument known as an anemometer. It was first developed in the 15th century and has since been used by meteorologists around the world.

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Hurricane, a definition -

In order for a tropical cyclone to be classified as a hurricane, it must have one-minute-average maximum sustained winds of at least 74 mph (119 km/h) and a height of 32.8 feet (10 meters) above the surface.

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Tropical depression -

Before a tropical cyclone is considered a hurricane, it starts as a tropical depression, the weakest form of a cyclone with sustained wind speeds of up to 38 mph (62 km/h). Although not as severe as hurricanes, tropical depressions can still cause flooding and damage, especially when they stall over land.

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Tropical storm -

Once a tropical depression reaches sustained wind speeds of 39 to 73 mph (63–118 km/h), it is classified as a tropical storm. These storms are less destructive than hurricanes but can still produce significant rainfall and strong winds. So how does the Saffir–Simpson scale categorize actual hurricanes?

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Categories -

The Saffir-Simpson scale is divided into five categories based on wind speeds. Categories 1 to 5 increase in intensity and potential damage. This structured scale helps forecasters communicate the severity of upcoming storms to the public.

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Category 1 -

Category 1 hurricanes have sustained wind speeds of 74 to 95 mph (119–153 km/h). These storms are considered the least severe in terms of wind damage but can still cause power outages, minor flooding, and coastal erosion.

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Category 2 -

Hurricanes classified as Category 2 have wind speeds ranging from 96 to 110 mph (154–177 km/h). These storms can cause more extensive damage, particularly to roofs, trees, mobile homes, and poorly constructed buildings.

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Category 3 -

Category 3 hurricanes, also known as major hurricanes, feature wind speeds of 111 to 129 mph (178–208 km/h). These storms can cause significant structural damage to homes and buildings, lead to widespread power outages, and even have the strength to uproot trees.

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Category 4 -

With wind speeds between 130 and 156 mph (209–251 km/h), Category 4 hurricanes are capable of causing catastrophic damage. Entire communities can be leveled, with widespread devastation to infrastructure, homes, and the environment.

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Category 5 -

Category 5 is the most severe level on the Saffir-Simpson scale, with wind speeds of 157 mph (252 km/h) or higher. These storms can cause total destruction, widespread flooding, and massive loss of life if not properly prepared for. Virtually every tree in the hurricane’s vicinity is uprooted, while steel and concrete structures also sustain damage.

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Deadliest hurricane -

In terms of sustained wind speed, Hurricane Patricia was the most powerful tropical cyclone in the entirety of recorded history. The Category 5 hurricane made landfall in Mexico in 2015 and reached top wind speeds of 215 mph (345 km/h). Luckily, only 13 souls perished in the disaster.

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Storm surge -

While the Saffir-Simpson scale primarily focuses on wind speed, storm surge (which is the rise in seawater level during a storm) remains one of the most deadly aspects of hurricanes.

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The Beaufort scale -

Before the Saffir-Simpson scale, the Beaufort Wind Force Scale was commonly used to describe wind speeds. Created in the 19th century, it was initially designed for sailors but later helped meteorologists assess storm intensity based on wind forces.

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Satellites -

The advent of weather satellites in the 1960s revolutionized hurricane monitoring. Satellites provide images and data on storm development and trajectory, giving meteorologists more precise information to categorize storms.

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Category 6 -

Over the years, many scientists have criticized the Saffir-Simpson scale under the claim that it simplifies hurricanes too much. Not only have meteorologists advocated for a scale that accounts for factors like storm surge, rainfall, and population density, but they have also suggested adding a Category 6 for storms with winds greater than 180 mph (290 km/h).

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Tornadoes -

For tornadoes, which occur over land, the Fujita scale is used to measure their intensity across six categories of structural damage, F0 to F5. In the US in 2007, this scale was decommissioned in favor of the more accurate Enhanced Fujita scale.

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Location -

The Saffir–Simpson hurricane wind scale is only used to categorize storms that are form in the Atlantic Ocean and northern Pacific Ocean east of the International Date Line. Because of this, only the American continents use the scale, while other places use different classifications.

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Western Pacific -

Tropical cyclones that form in the Northern Hemisphere between the 180th meridian and Thailand are monitored by the Japan Meteorological Agency. Cyclones are classified either as tropical storms or more extreme typhoons, with each classification divided into three categories of increasing intensity.

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North Indian Ocean -

Tropical cyclones in the North Indian Ocean are monitored by the India Meteorological Department in New Delhi. The department’s scale uses seven different classifications for storms, and cyclones that originate in the Arabian Sea are given the suffix “A,” while those from the Bay of Bengal receive the suffix “B.”

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South-West Indian Ocean -

In the Southern Hemisphere, cyclones to the east of Africa are monitored by the La Réunion tropical cyclone center, which is overseen by the French meteorological administration Météo-France. Their seven-scale system is used in various French territories, including New Caledonia and French Polynesia.

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Australia and Fiji -

Tropical cyclones that form in the Southern Hemisphere of the Pacific Ocean are monitored by multiple centers in Australia, Fiji, New Zealand, and Indonesia. Australia’s Bureau of Meteorology uses a five-point scale that measures cyclones according to 10-minute sustained wind speeds rather than one-minute.

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Formation -

Hurricanes form over warm ocean waters, typically above 80°F (26.5°C). The process begins when moist air rises, which creates low pressure at the surface. As more warm air rises, it cools and condenses, forming clouds and releasing latent heat, which fuels the storm.

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Coriolis effect -

The Coriolis effect (caused by Earth's rotation) helps hurricanes form by causing the storm to spin. In the Northern Hemisphere, hurricanes rotate counterclockwise, while in the Southern Hemisphere they rotate clockwise. In both hemispheres, hurricanes move east to west.

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Weakening a hurricane -

As hurricanes move over cooler waters or land, they lose their primary source of energy: warm water. Increased wind shear or dry air can also disrupt the storm's organization, causing it to weaken and eventually dissipate.

Sources: (National Weather Service) (National Oceanic and Atmospheric Administration) (National Hurricane Center) (Britannica)

See also: Climate change—how extreme weather is affecting our world

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