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).
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).
[4] In 1973, the scale was introduced to the general public,[5] and saw widespread use after Neil Frank replaced Simpson at the helm of the NHC in 1974.
[6] 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.
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.
The NHC and the Central 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.
[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), and Oscar (2024).
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), and Francine (2024).
These storms can cause some structural damage to small residences and utility buildings, particularly those of wood frame or manufactured materials with minor curtain wall failures.
[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), and Rafael (2024).
Heavy, irreparable damage and near-complete destruction of gas station canopies and other wide span overhang type structures are common.
[11] The 1900 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), and Helene (2024).
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 or concrete/cement block and have hipped 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.
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), and Otis (2023) (the only Pacific hurricane to make landfall at Category 5 intensity).
[13][25] Fresh calls were made for consideration of the issue after Hurricane 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.
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 (the 1935 Labor Day hurricane, Allen, Gilbert, Mitch, Rita, Wilma, Irma, Dorian, and Milton).
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, and Patricia).
[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 the effects of climate change and warming ocean temperatures part of that research.