The classifications are intended primarily for use in measuring the potential damage and flooding a hurricane will cause upon landfall, although they have been criticized as being too simple. Officially, the Saffir-Simpson Hurricane Scale is used only to describe hurricanes forming in the Atlantic Ocean and northern Pacific Ocean east of the International Date Line. Other areas use different classification scales to label these storms, which are called "cyclones" or "typhoons", depending on the area.
The initial scale was developed by Saffir, a structural engineer, who in 1969 went on commission for the United Nations to study low-cost housing in hurricane-prone areas. While performing the study, Saffir realized there was no simple scale for describing the likely effects of a hurricane. Mirroring the utility of the Richter magnitude scale in describing earthquakes, he devised a 1–5 scale based on wind speed that showed expected damage to structures. Saffir gave the scale to the NHC, and Simpson added the effects of storm surge and flooding. The scale does not take into account rainfall or location, which means a Category 2 hurricane which hits a major city will likely do far more damage than a Category 5 hurricane that hits a rural area.
The scale is roughly logarithmic in wind speed, and the top wind speed for Category "c" (c=1, 2, 3, or 4) can be expressed as miles per hour rounded to the nearest multiple of 5.
The five categories are, in order of increasing intensity:
|Sustained winds||33–42 m/s||64–82 kt|| |
Gaston at landfall
|119–153 km/h||74–95 mph|
|Storm surge||1.2–1.5 m||4–5 ft|
|Central pressure||980–989 mbar||28.94 inHg|
|Sustained winds||43–49 m/s||83–95 kt|| |
Alma approaching land
|154–177 km/h||96–110 mph|
|Storm surge||1.8–2.4 m||6–8 ft|
|Central pressure||965–979 mbar||28.50–28.91 inHg|
Hurricanes that peaked at Category 2 intensity, and made landfall while still in that category include Carol (1954), Diana (1990), Erin (1995), Alma (1996), Marty, Juan and Isabel (all 2003) and Dolly (2008).
|Sustained winds||50–58 m/s||96–113 kt|| |
Alicia approaching Texas
|178–209 km/h||111–130 mph|
|Storm surge||2.7–3.7 m||9–12 ft|
|Central pressure||945–964 mbar||27.91–28.47 inHg|
|Sustained winds||59–69 m/s||114–135 kt|| |
Ike, the largest Atlantic hurricane ever, coming over the Lesser Antilles
|210–249 km/h||131–155 mph|
|Storm surge||4.0–5.5 m||13–18 ft|
|Central pressure||920–944 mbar||27.17–27.88 inHg|
Hurricanes of this intensity are extremely dangerous to populated areas. Hurricane Ike was the most destructive Category 4 tropical cyclone in recorded history, causing damage in excess of $31.5 billion (2008 USD). With a storm surge of a Category 5 height though the windspeeds were that of a Category 2-3, Ike brought on the greatest recorded storm surge of any Category 4 Altantic tropical cyclone. Ike also went on to become the most massive Altantic tropical cyclone ever recorded. Use of radius of outermost closed isobar statistics indicate that Hurricane Ike was the largest tropical cyclone ever observed in the Atlantic basin. The Galveston Hurricane of 1900, the deadliest natural disaster to hit the United States, would be classified as Category 4 if it occurred today. Other examples of storms at this intensity are Hazel (1954), Carmen (1974), Iniki (1992), Luis (1995), Iris (2001), Charley (2004), and Gustav (2008).
|Sustained winds||≥70 m/s||≥136 kt|| |
Katrina approaching the Gulf Coast
|≥250 km/h||≥156 mph|
|Storm surge||≥5.5 m||≥19 ft|
|Central pressure||<920 mbar||<27.17 inHg|
Category 5 is the highest category a tropical cyclone can obtain in 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. 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. Only a few types of structures are capable of surviving intact, and only if located at least three to five miles (four to eight km) inland. They include office, condominium and apartment buildings and hotels that are of solid concrete or steel frame construction, public 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.
The storm's flooding causes major damage to the lower floors of all structures near the shoreline, and many coastal structures can be completely flattened or washed away by the storm surge. Storm surge damage can occur up to four city blocks inland, with flooding, depending on terrain, reaching six to seven blocks inland. Massive evacuation of residential areas may be required if the hurricane threatens populated areas.
Storms of this intensity can be severely damaging. Historical examples that reached the Category 5 status and made landfall as such include the Labor Day Hurricane of 1935, the 1959 Mexico Hurricane, Camille in 1969, Gilbert in 1988, Andrew in 1992, and Dean and Felix in 2007.
According to Robert Simpson, there is no reason 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. If the wind speed of the hurricane is above 156 mph (250 km/h), then the damage to a building will be "serious no matter how well it's engineered". However, the result of new technologies in construction leads some to suggest that an increase in the number of categories is necessary.
NAGS HEAD MAY RESTRICT DESIGN OF BIG HOMES PLAN CALLS FOR PORCHES, GABLED ROOFS, OTHER TOUCHES TO GIVE LARGER HOUSES MORE CHARACTER.(LOCAL)
Sep 17, 2002; Byline: MICHELLE WAGNER THE VIRGINIAN-PILOT\ NAGS HEAD -- The Nags Head Planning Board will consider a proposed ordinance tonight...