| Category | m/s | knots | mph | km/h |
|---|---|---|---|---|
| 5 | ≥ 70 | ≥ 137 | ≥ 157 | ≥ 252 |
| 4 | 58–70 | 113–136 | 130–156 | 209–251 |
| 3 | 50–58 | 96–112 | 111–129 | 178–208 |
| 2 | 43–49 | 83–95 | 96–110 | 154–177 |
| 1 | 33–42 | 64–82 | 74–95 | 119–153 |
| TS | 18–32 | 34–63 | 39–73 | 63–118 |
| TD | ≤ 17 | ≤ 33 | ≤ 38 | ≤ 62 |
TheSaffir–Simpson hurricane wind scale (SSHWS) is atropical cyclone intensity scale that classifieshurricanes—which in theWestern Hemisphere aretropical cyclones that exceed the intensities oftropical depressions andtropical storms—into five categories distinguished by the intensities of their sustainedwinds. This measuring system was formerly known as theSaffir–Simpson hurricane scale, orSSHS.
To be classified as a hurricane, atropical cyclone must have one-minute-averagemaximum sustained winds at 10 m (33 ft) above the surface of at least 74 mph (64 kn, 119 km/h; Category 1).[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 andflooding a hurricane will cause uponlandfall.
The Saffir–Simpson hurricane wind scale is based on the highestwind speed averaged over a one-minute interval 10 m above the surface. Although the scale shows wind speeds in continuous speed ranges, the USNational Hurricane Center and theCentral 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.[2]
The Saffir–Simpson hurricane wind scale is used officially only to describehurricanes that form in the Atlantic Ocean andnorthern Pacific Ocean east of theInternational Date Line. Other areas usedifferent scales to label these storms, which are calledcyclones ortyphoons, depending on the area. These areas (except theJTWC) usethree-minute orten-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 aten-minute interval (usually 12% less intense).[3]
There is somecriticism 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. 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 2024[update].
In 1971, the scale was developed bycivil engineerHerbert Saffir and meteorologistRobert Simpson, who at the time was director of the U.S.National Hurricane Center (NHC).[4] In 1973, the scale was introduced to the general public,[5] and saw widespread use afterNeil Frank replaced Simpson at the helm of the NHC in 1974.[6]
The scale was created by Herbert Saffir, astructural engineer, who in 1969 was commissioned by theUnited Nations to study low-cost housing in hurricane-prone areas.[7] In 1971, while conducting the study, Saffir realized there was no simple scale for describing the likely effects of a hurricane.[8] By using subjective damage-based scales for earthquake intensity like theModified Mercalli intensity scale orMSK-64 intensity scale and the objective numerical gradation method of theRichter 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.[8][9]
| Grade | Wind Speed Range |
| Grade 1 | 120 - 140 km/h |
| Grade 2 | 151-180 km/h |
| Grade 3 | 181-210 km/h |
| Grade 4 | 211-240 km/h |
| Grade 5 | 241+ km/h |
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 addedstorm surge height ranges, adding barometric pressure ranges later on. In 1975, the Saffir-Simpson Scale was first published publicly.[6][8][10]
In 2009, the NHC eliminated pressure and storm surge ranges from the categories, transforming it into a pure wind scale, called the Saffir–Simpson Hurricane Wind Scale (Experimental) [SSHWS].[11] The updated scale became operational on May 15, 2010.[12] The scale excludes flood ranges,storm surge estimations, rainfall, and location, which means a Category 2 hurricane that hits a major city will likely do far more cumulative damage than a Category 5 hurricane that hits a rural area.[13] The agency cited examples of hurricanes as reasons for removing "scientifically inaccurate" information, includingHurricane Katrina (2005) andHurricane Ike (2008), which both had stronger than estimated storm surges, andHurricane Charley (2004), which had weaker than estimated storm surge.[14] Since being removed from the Saffir–Simpson hurricane wind scale, storm surge prediction and modeling is handled by computer numerical models such asADCIRC andSLOSH.
In 2012, the NHC extended the wind speed range for Category 4 by 1 mph in both directions, to 130–156 mph, with corresponding changes in the other units (113–136 kn, 209–251 km/h), instead of 131–155 mph (114–135 kn, 210–249 km/h). The NHC and theCentral Pacific Hurricane Center assign tropical cyclone intensities in 5 knot increments, and then convert to mph and km/h with a similar rounding for other reports. So an intensity of 115 kn is rated Category 4, but the conversion to miles per hour (132.3 mph) would round down to 130 mph, making it appear to be a Category 3 storm. Likewise, an intensity of 135 kn (~155 mph, and thus Category 4) is 250.02 km/h, which, according to the definition used before the change would be Category 5.[11]
To resolve these issues, the NHC had been obliged to incorrectly report storms with wind speeds of 115 kn as 135 mph, and 135 kn as 245 km/h. The change in definition allows storms of 115 kn to be correctly rounded down to 130 mph, and storms of 135 kn to be correctly reported as 250 km/h, and still qualify as Category 4. Since the NHC had previously rounded incorrectly to keep storms in Category 4 in each unit of measure, the change does not affect the classification of storms from previous years.[11] The new scale became operational on May 15, 2012.[15]
| Saffir–Simpson scale | ||||||
| TD | TS | C1 | C2 | C3 | C4 | C5 |
The scale separates hurricanes into five different categories based on wind. The U.S. National Hurricane Center classifies hurricanes of Category 3 and above asmajor hurricanes. The Joint Typhoon Warning Center classifies typhoons of 150 mph (240 km/h) or greater (strong Category 4 and Category 5) assuper typhoons. Most weather agencies use the definition for sustained winds recommended by theWorld Meteorological Organization (WMO), which specifies measuring winds at a height of 33 ft (10.1 m) for 10 minutes, and then taking the average. By contrast, the U.S.National Weather Service,Central Pacific Hurricane Center and theJoint Typhoon Warning Center define sustained winds as average winds over a period of one minute, measured at the same 33 ft (10.1 m) height,[16][17] and that is the definition used for this scale.
The five categories are described in the following subsections, in order of increasing intensity.[18] Example hurricanes for each category are limited to those which made landfall at their maximum achieved category on the scale.
| Category 1 | |
|---|---|
| Sustained winds | Most recent landfall |
| 33–42 m/s 64–82 kn 119–153 km/h 74–95 mph |  Oscar in 2024 at landfall inCuba |
Very dangerous winds will produce some damage
Category 1 storms usually cause no significant structuraldamage to most well-constructed permanent structures. They can topple unanchoredmobile homes, as well as uproot or snap weak trees. Poorly attached roof shingles or tiles can blow off.Coastal flooding andpier damage are often associated with Category 1 storms. Power outages are typically widespread to extensive, sometimes lasting several days. Even though it is the least intense type of hurricane, they can still produce widespread damage and can be life-threatening storms.[11]
Hurricanes that peaked at Category 1 intensity and made landfall at that intensity include:Juan (1985),Ismael (1995),Danny (1997),Stan (2005),Humberto (2007),Isaac (2012),Manuel (2013),Earl (2016),Newton (2016),Nate (2017),Barry (2019),Lorena (2019),Hanna (2020),Isaias (2020),Nicholas (2021),Julia (2022),Lisa (2022),Nicole (2022),Debby (2024), andOscar (2024).
| Category 2 | |
|---|---|
| Sustained winds | Most recent landfall |
| 43–49 m/s 83–95 kn 154–177 km/h 96–110 mph |  Francine in 2024 at landfall nearMorgan City, Louisiana |
Extremely dangerous winds will cause extensive damage
Storms of Category 2 intensity often damage roofing material, sometimes exposing the roof, and inflict damage upon poorly constructed doors and windows. Poorly constructed signs and piers can receive considerable damage and many trees are uprooted or snapped. Mobile homes, whether anchored or not, are typically damaged and sometimes destroyed, and manymanufactured homes suffer structural damage. Small craft in unprotected anchorages may break theirmoorings. Extensive to near-total power outages and scattered loss of potable water are likely, possibly lasting many days.[11]
Hurricanes that peaked at Category 2 intensity and made landfall at that intensity include:Alice (1954),Ella (1958),Ginny (1963),Fifi (1974),Diana (1990),Gert (1993),Rosa (1994),Erin (1995),Alma (1996),Marty (2003),Juan (2003),Alex (2010),Tomas (2010),Carlotta (2012),Arthur (2014),Sally (2020),Olaf (2021),Rick (2021),Agatha (2022), andFrancine (2024).
| Category 3 | |
|---|---|
| Sustained winds | Most recent landfall |
| 50–58 m/s 96–112 kn 178–208 km/h 111–129 mph |  Rafael in 2024 just prior to its landfall inCuba |
Devastating damage will occur
Tropical cyclones of Category 3 and higher are described asmajor hurricanes in the Atlantic, Eastern Pacific, and Central Pacificbasins. These storms can cause some structural damage to small residences and utility buildings, particularly those of wood frame or manufactured materials with minorcurtain wall failures. Buildings that lack a solid foundation, such as mobile homes, are usually destroyed, andgable-end roofs are peeled off.[11]
Manufactured homes usually sustain severe and irreparable damage. Flooding near the coast destroys smaller structures, while larger structures are struck by floating debris. A large number of trees are uprooted or snapped, isolating many areas. Terrain may be flooded well inland. Near-total to total power loss is likely for up to several weeks. Home water access will likely be lost or contaminated.[11]
Hurricanes that peaked at Category 3 intensity and made landfall at that intensity include:Easy (1950),Carol (1954),Hilda (1955),Audrey (1957),Olivia (1967),Ella (1970),Eloise (1975),Alicia (1983),Elena (1985),Roxanne (1995),Fran (1996),Isidore (2002),Jeanne (2004),Lane (2006),Karl (2010),Otto (2016),Zeta (2020),Grace (2021),John (2024), andRafael (2024).
| Category 4 | |
|---|---|
| Sustained winds | Most recent landfall |
| 58–70 m/s 113–136 kn 209–251 km/h 130–156 mph |  Helene in 2024 just prior to itsFlorida Big Bend landfall |
Catastrophic damage will occur
Category 4 hurricanes tend to produce more extensive curtainwall failures, with some completestructural failure on small residences. Heavy, irreparable damage and near-complete destruction of gas station canopies and other wide span overhang type structures are common. Mobile and manufactured homes are often flattened. Most trees, except for the hardiest, are uprooted or snapped, isolating many areas. These storms cause extensivebeach erosion. Terrain may be flooded far inland. Total and long-lived electrical and water losses are to be expected, possibly for many weeks.[11]
The1900 Galveston hurricane, the deadliest natural disaster to hit the United States, peaked at an intensity that corresponds to a modern-day Category 4 storm. Other examples of storms that peaked at Category 4 intensity and made landfall at that intensity include:Hazel (1954),Gracie (1959),Donna (1960),Carla (1961),Flora (1963),Betsy (1965),Celia (1970),Carmen (1974),Madeline (1976),Frederic (1979),Joan (1988),Iniki (1992),Charley (2004),Dennis (2005),Ike (2008),Harvey (2017),Laura (2020),Ida (2021),Lidia (2023), andHelene (2024).
| Category 5 | |
|---|---|
| Sustained winds | Most recent landfall |
| ≥ 70 m/s ≥ 137 kn ≥ 252 km/h ≥ 157 mph |  Otis in 2023 nearing its landfall inAcapulco, Mexico |
Catastrophic damage will occur
Category 5 is the highest category of the Saffir–Simpson scale. These storms cause complete roof failure on many residences and industrial buildings, and some complete building failures with small utility buildings blown over or away. The collapse of many wide-span roofs and walls, especially those with no interior supports, is common. Very heavy and irreparable damage to many wood-frame structures and total destruction to mobile/manufactured homes is prevalent.[11]
Only a few types of structures are capable of surviving intact, and only if located at least 3 to 5 miles (5 to 8 km) inland. They include office, condominium and apartment buildings and hotels that are of solid concrete or steel frame construction, multi-story concrete parking garages, and residences that are made of either reinforced brick orconcrete/cement block and havehipped roofs with slopes of no less than 35 degrees from horizontal and no overhangs of any kind, and if the windows are either made of hurricane-resistant safety glass or covered with shutters. Unless most of these requirements are met, the catastrophic destruction of a structure may occur.[11]
The storm's flooding causes major damage to the lower floors of all structures near the shoreline. Many coastal structures can be completely flattened or washed away by the storm surge. Virtually all trees areuprooted or snapped and some may be debarked, isolating most affected communities. Massiveevacuation of residential areas may be required if the hurricane threatens populated areas. Total and extremely long-lived power outages and water losses are to be expected, possibly for up to several months.[11]
Historical examples of storms that made landfall at Category 5 status include:"Cuba" (1924),"Okeechobee" (1928),"Bahamas" (1932),"Cuba–Brownsville" (1933),"Labor Day" (1935),Janet (1955),Inez (1966),Camille (1969),Edith (1971),Anita (1977),David (1979),Gilbert (1988),Andrew (1992),Dean (2007),Felix (2007),Irma (2017),[19]Maria (2017),[20]Michael (2018),[21]Dorian (2019), andOtis (2023) (the only Pacific hurricane to make landfall at Category 5 intensity).
Some scientists, includingKerry Emanuel and Lakshmi Kantha, have criticized the scale as being too simplistic, namely that the scale takes into account neither the physical size of a storm nor the amount ofprecipitation it produces.[13] They and others point out that the Saffir–Simpson scale, unlike themoment magnitude scale used to measureearthquakes, is not continuous, and isquantized into a small number of categories. Proposed replacement classifications include the Hurricane Intensity Index, which is based on thedynamic pressure caused by a storm's winds, and the Hurricane Hazard Index, which is based on surface wind speeds, theradius of maximum winds of the storm, and itstranslational velocity.[22][23] Both of these scales are continuous, akin to the Richter scale.[24] However, neither of these scales has been used by officials.[citation needed]
After the series of powerful storm systems of the2005 Atlantic hurricane season, as well as afterHurricane Patricia, a few newspaper columnists and scientists brought up the suggestion of introducing Category 6. They have suggested pegging Category 6 to storms with winds greater than 174 or 180 mph (78 or 80 m/s; 151 or 156 kn; 280 or 290 km/h).[13][25] Fresh calls were made for consideration of the issue afterHurricane Irma in 2017,[26] which was the subject of a number of seemingly credible false news reports as a "Category 6" storm,[27] partly in consequence of so many local politicians using the term. Only a few storms of this intensity have been recorded.
Of the 42 hurricanes currently considered to have attained Category 5 status in the Atlantic, 19 had wind speeds at 175 mph (78 m/s; 152 kn; 282 km/h) or greater. Only 9 had wind speeds at 180 mph (80.5 m/s; 156 kn; 290 km/h) or greater (the1935 Labor Day hurricane,Allen,Gilbert,Mitch,Rita,Wilma,Irma,Dorian, andMilton). Of the 21 hurricanes currently considered to have attained Category 5 status in the eastern Pacific, only 5 had wind speeds at 175 mph (78 m/s; 152 kn; 282 km/h) or greater (Patsy,John,Linda,Rick, andPatricia). Only 3 had wind speeds at 180 mph (80.5 m/s; 156 kn; 290 km/h) or greater (Linda, Rick, and Patricia).
Most storms which would be eligible for this category weretyphoons in the western Pacific, most notably typhoonsTip,Halong,Mawar, andBolaven in 1979, 2019, 2023 and 2023 respectively, each with sustained winds of 190 mph (305 km/h),[28] and typhoonsHaiyan,Meranti,Goni, andSurigae in 2013, 2016, 2020 and 2021 respectively, each with sustained winds of 195 mph (315 km/h).
Occasionally, suggestions of using even higher wind speeds as the cutoff have been made. In a newspaper article published in November 2018,NOAA research scientist Jim Kossin said that the potential for more intense hurricanes was increasing as theclimate warmed, and suggested that Category 6 would begin at 195 mph (85 m/s; 170 kn; 315 km/h), with a further hypothetical Category 7 beginning at 230 mph (105 m/s; 200 kn; 370 km/h).[29] In 2024 another proposal to add "Category 6" was made, with a minimum wind speed of 192 mph (309 km/h), with risk factors such as theeffects of climate change and warming ocean temperatures part of that research.[30] In the NHC area of responsibility, only Patricia had winds greater than 190 mph (85 m/s; 165 kn; 305 km/h).
According to Robert Simpson, co-creator of the scale, there are no reasons for a Category 6 on the Saffir–Simpson scale because it is designed to measure the potential damage of a hurricane to human-made structures. Simpson explained that "... when you get up into winds in excess of 155 mph (249 km/h) you have enough damage if that extreme wind sustains itself for as much as six seconds on a building it's going to cause rupturing damages that are serious no matter how well it's engineered."[6] Nonetheless, the counties ofBroward andMiami-Dade in Florida have building codes which require that critical infrastructure buildings be able to withstand Category 5 winds.[31]
For US Navy interests, the factor 0.88 is used in going from a 1-minute system to a 10-minute system such that TEN-MINUTE MEAN = 0.88 * ONE-MINUTE MEAN or ONE-MINUTE MEAN = 1.14 * TEN-MINUTE MEAN.Retrieved on 2018-10-07.
