|Saffir–Simpson Hurricane Scale|
|Category||Wind speed||Storm surge|
The scale separates hurricanes into five different categories based on wind, central barometric pressure, and storm surge. The U.S. National Hurricane Center classifies hurricanes of Category 3 and above as major hurricanes. Most weather agencies use the definition for sustained winds recommended by the World Meteorological Organization (WMO), which specifies measuring winds at a height of 33 ft (10 m) for 10 minutes, and then taking the average. By contrast, the U.S. National Weather Service defines sustained winds as average winds over a period of one minute, measured at the same 33 ft (10 m) height. Central pressure and storm surge values are approximate and often dependant on other factors, such as the size of the storm and the location. Intensity of example hurricanes is from both the time of landfall and the maximum intensity.
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||
Claudette near 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|
Category 1 storms usually cause no significant structural damage to building structures; however, they can topple unanchored mobile homes, as well as uproot or snap trees. Poorly attached roof shingles or tiles can blow off. Coastal flooding and pier damage are often associated with Category 1 storms.
|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|
Storms of Category 2 are strong enough that they can lift a house, and inflict damage upon poorly constructed doors and windows. Vegetation, poorly constructed signs, and piers can receive considerable damage. Mobile homes, whether anchored or not, are typically damaged, and many manufactured homesalso suffer structural damage. Small craft in unprotected anchorages may break their moorings.
|Sustained winds||50–58 m/s||96–113 kt||
Jeanne over the Bahamas
|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|
Tropical cyclones of Category 3 and higher are described as major hurricanes in the Atlantic or Eastern Pacific basins. These storms can cause some structural damage to small residences and utility buildings, particularly those of wood frame or manufactured materials with minor curtainwall failures. Buildings that lack a solid foundation, such as mobile homes, are usually destroyed, and gable-end roofs are peeled off. Manufactured homes usually sustain severe and irreparable damage. Flooding near the coast destroys smaller structures, while larger structures are struck by floating debris. Additionally, terrain may be flooded well inland.
|Sustained winds||59–69 m/s||114–135 kt||
Flossie in the Central Pacific
|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|
See also: List of Category 4 Atlantic hurricanes
Category 4 hurricanes tend to produce more extensive curtainwall failures, with some complete roofstructural 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 leveled. These storms cause extensive beach erosion, while terrain may be flooded far inland.
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 Atlantic tropical cyclone. Ike also went on to become the most massive Atlantic 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, peaked at an intensity that corresponds to a modern-day Category 4 storm. Other examples of storms at this intensity are Hazel (1954), Carmen (1974), Iniki (1992),Luis (1995), Iris (2001), Charley (2004).
|Sustained winds||≥70 m/s||≥136 kt||
Gilbert in the Caribbean Sea
|≥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, and Gilbert in 1988, Andrew in 1992, Dean, and Felix (2007).