How the Saffir-Simpson Hurricane Wind Scale Works

How the Saffir-Simpson Scale Works

Quiz Yourself

Stores are disemboweled, roads are jam-packed and people are in a total frenzy.
Yes, those are the harrowing scenes that occur when a category 5 hurricane sets its eyes on an area.
But, just what makes the category of a hurricane such a big deal?
In this lesson, you will learn how hurricane categories or the Saffir-Simpson Hurricane Wind Scale works.

The Saffir-Simpson scale was developed by structural engineer Herbert Saffir and Meteorologist Robert Simpson. It became operational in 1973.

By the dawn of the 1970s, the United States became quite accustomed to and aware of the destructive potential of hurricanes. Catastrophic hurricanes such as Hazel, Cleo and Betsy have already wreaked havoc on the population.
But, something was missing: there was no thorough, systematic method of quantifying the strength of hurricanes. Realizing this during his studies, structural engineer Herbert Saffir created a scale rated from one to five.
Later, meteorologist Robert Simpson also contributed to the scale by factoring in flooding and storm surge. The scale became available to the public by 1974 [1].

Figure 1: A simplified view of the Saffir-Simpson Scale.

The Saffir-Simpson scale is only based on potential wind damage from a hurricane.

The saffir-Simpson scale ranges from category one to category five, with category five being the most destructive. Hurricanes of category three intensity or higher are considered to be major hurricanes. They have an "M" symbol on tracking maps.
The scale is basely solely on wind. After it was revised in 2010, it no longer included factors such as storm surge, atmospheric pressure and flooding. It also does not include tropical cyclones weaker than a hurricane. As such, tropical storms and tropical depressions are not part of the Saffir-Simpson scale.

Figure 2: The "M" symbol represents a major hurricane. NOAA.

What About Other Parts of the World ?
The Saffir-Simpson scale is mainly used in the western hemisphere, particularly North America, central America, the Caribbean, etc. Other parts of the world such as Australia, Japan and India use other scales to rate tropical cyclone intensity.

1. After 2010, air pressure and storm surge were no longer included in the scale.
2. In 2012, the wind speed range for a category four hurricane became 130 MPH to 156 MPH. For a category three Hurricane, it became 111 MPH to 129 MPH.
3. The new, official name of the scale is the Saffir-Simpson Hurricane Wind Scale.

As mentioned earlier, the scale doesn't include storm surge and flooding. But, that was not always the case. Before 2010, the scale used to include atmospheric pressure and storm surge.
Storm surge in particular does not always correlate with maximum sustained winds. For example, hurricane Charley was a strengthening, powerful category 4 hurricane at landfall. Yet, it produced a paltry storm surge for a hurricane of its caliber.
In contrast, Hurricane Katrina made landfall as a 125-MPH category 3 Hurricane, but had a much higher storm surge than Hurricane Charley. Granted, one clear reason for this was because Hurricane Katrina covered a greater distance. It was thus able to pile up more water. But, then that would also mean making the scale more complicated by including the overall size of the storm into it.
Therefore, to keep things simple, it was announced in the National Hurricane Plans of 2010 that the Saffir-Simpson scale would no longer include storm surge and atmospheric pressure. Rather, it would only be a wind scale — hence the name Saffir-Simpson Hurricane Wind Scale [2].
Moreover, to facilitate conversion, the National Hurricane Center adjusted the wind speed ranges for category three and four hurricanes in 2012. As such, the Category three hurricanes have been adjusted from 111-130 MPH to 111-129 MPH; and category four hurricanes have been adjusted from 131-155 MPH to 130-156 MPH [3].

Figure 3: Hurricane Andrew as a powerful category five storm. NOAA.

A big difference! With each complete category upgrade, the damage potential of a hurricane increases exponentially. For example, it might seem like a strong, 150-MPH category four hurricane is twice as destructive as a 75-MPH category hurricane.
The truth is it's not a twofold, but a 256 times increase in damage potential. The reason is because each incremental increase in wind significantly increases the amount of damage that can be done on an object.
This explains why major hurricanes (category three or higher) cause 85 percent of all the damage despite the fact they account for just 24 percent of all tropical cyclones that make landfall [4].
Therefore, when you see a storm is upgraded a category or two, pay attention and take it seriously!