Hurricane Categories

In the 1970s, NOAA (the National Oceanic and Atmospheric Administration) developed a disaster potential scale to aid forecasters in predicting the destructive power of a hurricane called the Saffir-Simpson Hurricane Scale. According to the book Hurricane Watch by Bob Sheets and Jack Williams, the original categorical measurement levels were developed in 1971 by structural engineer Herbert Saffir as part of his work with the United Nations to assess the potential for wind damage to low cost housing. The following year, Saffir’s original work was expanded upon by Robert Simpson (then director of National Hurricane Center). While Saffir concentrated on wind damage, Simpson noted the effects of flooding, tides and storm surges.

In 1972, the Saffir-Simpson Hurricane Scale debuted (see Reference #1); it is only used to classify storms in the Atlantic Basin and northern Pacific Ocean east of the International Date Line (in other words, it is not used to classify typhoons and cyclones). Before Saffir and Simpson categorized hurricanes, they were known as either “major or minor” – after the implementation of the scale, the National Hurricane Center searched its own archives and classified every known major storm to hit the U.S. since 1886. Hebert Saffir died on November 22nd, 2007.

At the beginning of the 2009 Atlantic Basin hurricane season, NOAA “redefined” the Saffir-Simpson Hurricane Scale removing Robert Simpson’s references to storm surge. The new reference system was initially called the Saffir-Simpson Hurricane Wind Scale (Experimental); NOAA and the National Hurricane Center set out to develop a new storm surge, flooding and tides scale (logic would dictate the eventual categorization of a Saffir Wind Category Scale and a Simpson Tidal Surge Scale).

Storm surge is just as dangerous (and sometimes even more) than wind damage and somewhat unpredictable under the old Saffir-Simpson model. In 2008, an unexpected storm surge of 13 to 18 feet (usually associated with a Category 4 storm) accompanied Hurricane Ike (a Category 2 storm) when it made landfall in Texas. Conversely, 2004’s Hurricane Charley (the first of seven severe storms over a two year period to make landfall in the U.S.- see Reference #2 ) hit Florida as a Category 4 but only had a six to seven foot storm surge (something usually acquainted with a Category 2). The “dirty-side” of any system can cause massive flooding; in forecasting a storm surge, scientists have to take into account typography, tidal activity, wind speed and wind direction.

In taking action on a new scale, the NHC addressed concerns about non-evacuations by complacent residents ignoring storm surge warnings of areas not in a direct path of a storm, as well as any unnecessary mass exodus clogging potential evacuation routes and putting a strain on infrastructure. With the new separate scales (and better forecasting tools), meteorologists would be able to emphasize potential wind and flood danger for different areas. Other changes to the revised wind scale include a much more detailed prediction of damage, an associated aftermath of a hurricane’s devastation (in the form of power outages) and a grim no-nonsense assessment of the possibility of injury or death.

Here is the new Saffir-Simpson Hurricane Wind Scale (Categories 1-5) along with “tropical” definitions. At the bottom of this page is the old “pre-2009” Saffir-Simpson Hurricane Scale:

  • Tropical Disturbance: (No specific wind speed)
    A moving area of thunder storms in the Tropics that maintain its identity for 24 hours or more. As it organizes, look for it to develop into a tropical depression.
  • Tropical Depression:(Winds less than 39 mph)
    An organized weather system of clouds and thunderstorms. There is a defined circulation.
  • Tropical Storm: (Winds 39 mph-73 mph)
    An organized weather system of strong storms. Again, there is a defined circulation.
  • Category 1: (Winds 74 mph to 95 mph) – Minimal or Weak
    Damaging winds are expected. Some damage to building structures could occur, primarily to unanchored mobile homes (mainly pre-1994 construction). Some damage is likely to poorly constructed signs. Loose outdoor items will become projectiles, causing additional damage. Persons struck by windborne debris risk injury and possible death. Numerous large branches of healthy trees will snap. Some trees will be uprooted, especially where the ground is saturated. Many areas will experience power outages with some downed power poles.
  • Category 2: (Winds 96 mph to 110 mph) – Moderate
    Very strong winds will produce widespread damage. Some roofing material, door, and window damage of buildings will occur. Considerable damage to mobile homes (mainly pre-1994 construction) and poorly constructed signs is likely. A number of glass windows in high rise buildings will be dislodged and become airborne. Loose outdoor items will become projectiles, causing additional damage. Persons struck by windborne debris risk injury and possible death.. Numerous large branches will break. Many trees will be uprooted or snapped. Extensive damage to power lines and poles will likely result in widespread power outages that could last a few to several days.
  • Category 3: (Winds 111 mph to 130 mph) – Extensive or Strong
    Dangerous winds will cause extensive damage. Some structural damage to houses and buildings will occur with a minor amount of wall failures. Mobile homes (mainly pre-1994 construction) and poorly constructed signs are destroyed. Many windows in high rise buildings will be dislodged and become airborne. Persons struck by windborne debris risk injury and possible death. Many trees will be snapped or uprooted and block numerous roads. Near total power loss is expected with outages that could last from several days to weeks.
  • Category 4: (Winds 131 mph to 155 mph) – Extreme or Very Strong
    Extremely dangerous winds causing devastating damage are expected. Some wall failures with some complete roof structure failures on houses will occur. All signs are blown down. Complete destruction of mobile homes (primarily pre-1994 construction). Extensive damage to doors and windows is likely. Numerous windows in high rise buildings will be dislodged and become airborne. Windborne debris will cause extensive damage and persons struck by the wind-blown debris will be injured or killed. Most trees will be snapped or uprooted. Fallen trees could cut off residential areas for days to weeks. Electricity will be unavailable for weeks after the hurricane passes.
  • Category 5: (Winds greater than 155 mph) – Catastrophic or Devastating
    Catastrophic damage is expected. Complete roof failure on many residences and industrial buildings will occur. Some complete building failures with small buildings blown over or away are likely. All signs blown down. Complete destruction of mobile homes (built in any year). Severe and extensive window and door damage will occur. Nearly all windows in high rise buildings will be dislodged and become airborne. Severe injury or death is likely for persons struck by wind-blown debris. Nearly all trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last for weeks to possibly months.

Old Saffir-Simpson Hurricane Scale (pre 2009):

  • Category 1: (Winds 74 mph to 95 mph) – Minimal or Weak
    No real damage to building structures. Damage primarily to unanchored mobile homes, shrubbery and trees. Also, some coastal flooding and minor pier damage…
  • Category 2: (Winds 96 mph to 110 mph) – Moderate
    Some roofing material, door and window damage to buildings. Considerable damage to vegetation, mobile homes and piers. Coastal and low-lying escape routes flood 2-4 hours before arrival of center. Small craft in unprotected anchorages break moorings. Storm surge expected to be 6 to 8 feet…
  • Category 3: (Winds 111 mph to 130 mph) – Extensive or Strong
    Some structural damage to small residences and utility buildings with a minor amount of curtain-wall failures. Mobile homes are destroyed. Flooding near the coast destroys smaller structures with larger structures damaged by floating debris. Terrain continuously lower than five feet ASL (at sea level) may be flooded inland 8 miles or more. Storm surge expected to be nine to 12 feet…
  • Category 4: (Winds 131 mph to 155 mph) – Extreme or Very Strong
    More extensive curtain-wall failures with some complete roof structure failure on small residences. Major erosion of beach. Major damage to lower floors of structures near the shore. Terrain continuously lower than ten feet ASL may be flooded requiring massive evacuation of residential areas inland as far as 6 miles. Extensive damage expected to ships as big as oil barges and freighters caught in the path. Storm surge expected to be 13 to 18 feet…
  • Category 5: (Winds greater than 156 mph) – Catastrophic or Devastating
    Complete roof failure on many residences and industrial buildings. Some complete building failures with small utility buildings blown over or away. Major damage to lower floors of all structures located less than 15 feet ASL and within 500 yards of the shoreline. Massive evacuation of residential areas on low ground within 5 to 10 miles of the shoreline may be required. Storm surge expected over 19 feet…

Reference #1: Sheets, Bob and Jack Williams. Hurricane Watch. 1st. New York: Random House, 2001. Page 156.

Reference #2: In order (from 2004 to 2005), those seven storms were Charley, Frances, Ivan, Dennis, Katrina, Rita and Wilma.