Coastal Processes, Hazards, and Society

Measuring the Strength of Tropical Cyclones


Measuring the Strength of Tropical Cyclones

Before looking at examples of catastrophic storms, let’s review the ways they are quantified in terms of strength. The Saffir-Simpson Scale was developed in 1971 by civil engineer Herbert Saffir and meteorologist Robert Simpson, who at the time was director of the U.S. National Hurricane Center (NHC).

The scale uses the wind speeds and pressure of a storm to determine its strength. It did not originally take into account storm surge. The modified version of the Saffir-Simpson Scale on attempts to rectify this by assigning storm surge ranges to the scale. Please visit this site to learn about the classification of tropical cyclones (Categories of hurricanes and typhoons).

An abbreviated summary of this modified Saffir-Simpson scale is shown below.


Wind speeds/ surge

Types of Damage

Category 1 hurricane

74-95 mph (64-82 knots; 119-153 km/hr); surge 4-5 ft (1.2 – 1.7 m)

“Minimal”: Minimal damage to buildings, boats, trees, etc. Main threat is from heavy rainfall.

Category 2 hurricane

96-110 mph (83-95 knots; 154-177 km/hr); surge 6-8 ft (1.8 -2.6 m)

“Moderate”: Roof and window damage to buildings; severe damage to mobile homes. Some damage from storm surge.

Category 3 hurricane

111-130 mph (96-113 knots; 178-209 km/hr); surge 9-12 ft. (2.7 – 3.9 m);

“Extensive”: Structural damage to buildings; complete destruction of mobile homes. Storm surge destroys some buildings and causes shoreline erosion.

Category 4 hurricane

131-155 mph (114-135 knots; 210-249 km/hr); surge 13-18 ft (4 -5.5 m)

“Extreme”: Structural failure of some buildings. Severe coastal erosion. Hurricane force move winds far inland.

Category 5 hurricane; Super typhoon

Greater than 155 mph (135 knots; 249 km/hr) surge >18 ft (5.5 m).

“Catastrophic”: Catastrophic storm surge damage; Many buildings destroyed beyond repair.

Because storm surge is not well integrated into the Saffir Simpson Scale, it is often under-appreciated for the risk it poses when a hurricane comes ashore. It is the most dangerous part of any coastal hurricane impact and has been responsible for the majority of the deaths that have been recorded as a result of U.S. hurricanes. A good example is found in Hurricane Katrina. Although classified as category 3 upon landfall, Katrina was category 5 while in the Gulf of Mexico. Therefore, the storm surge, at more than 20 ft. fit the category 5 surge classification according to this modified scale.