Saffir–Simpson scale

The Saffir–Simpson hurricane wind scale (SSHWS) is a tropical cyclone intensity scale that classifies hurricanes—which in the Western Hemisphere are tropical cyclones that exceed the intensities of tropical depressions and tropical storms—into five categories distinguished by the intensities of their sustained winds. This measuring system was formerly known as the Saffir–Simpson hurricane scale, or SSHS.

To be classified as a hurricane, a tropical cyclone must have one-minute-average maximum sustained winds at 10 m (33 ft) above the surface of at least 74 mph (64 kn, 119 km/h; Category 1). The highest classification in the scale, Category 5, consists of storms with sustained winds of at least 157 mph (137 kn, 252 km/h). The classifications can provide some indication of the potential damage and flooding a hurricane will cause upon landfall.

The Saffir–Simpson hurricane wind scale is based on the highest wind speed averaged over a one-minute interval 10 m above the surface. Although the scale shows wind speeds in continuous speed ranges, the US National Hurricane Center and the Central Pacific Hurricane Center assign tropical cyclone intensities in 5-knot (kn) increments (e.g., 100, 105, 110, 115 kn, etc.) because of the inherent uncertainty in estimating the strength of tropical cyclones. Wind speeds in knots are then converted to other units and rounded to the nearest 5 mph or 5 km/h.

The Saffir–Simpson hurricane wind scale is used officially only to describe hurricanes that form in the Atlantic Ocean and northern Pacific Ocean east of the International Date Line. Other areas use different scales to label these storms, which are called cyclones or typhoons, depending on the area. These areas (except the JTWC) use three-minute or ten-minute averaged winds to determine the maximum sustained wind speed, creating an important difference which frustrates direct comparison between maximum wind speeds of storms measured using the Saffir–Simpson hurricane wind scale (usually 14% more intense) and those measured using a ten-minute interval (usually 12% less intense).

There is some criticism of the SSHWS for not accounting for rain, storm surge, and other important factors, but SSHWS defenders say that part of the goal of SSHWS is to be straightforward and simple to understand.^{[citation needed]} There have been proposals for the addition of higher categories to the scale, which would then set a maximum cutoff for Category 5, but none have been adopted as of October 2025^[update].

In 1971, the scale was developed by civil engineer Herbert Saffir and meteorologist Robert Simpson, who at the time was director of the U.S. National Hurricane Center (NHC). In 1973, the scale was introduced to the general public, and saw widespread use after Neil Frank replaced Simpson at the helm of the NHC in 1974.

The scale was created by Herbert Saffir, a structural engineer, who in 1969 was commissioned by the United Nations to study low-cost housing in hurricane-prone areas. In 1971, while conducting the study, Saffir realized there was no simple scale for describing the likely effects of a hurricane. By using subjective damage-based scales for earthquake intensity like the Modified Mercalli intensity scale or MSK-64 intensity scale and the objective numerical gradation method of the Richter scale as models, he proposed a simplified 1–5 grading scale as a guide for areas that do not have hurricane building codes. The grades were based on two main factors: objective wind gust speeds sustaining for 2–3 seconds at an elevation of 9.2 meters, and subjective levels of structural damage.

Saffir gave the proposed scale to the NHC for their use, where Simpson changed the terminology from "grade" to "category", organized them by sustained wind speeds of 1 minute duration, and added storm surge height ranges, adding barometric pressure ranges later on. In 1975, the Saffir–Simpson Scale was first published publicly.