Like the 10 point Richter Scale, the Saffir-Simpson Scale’s purpose is to simplify our understanding of hurricanes using a rating system. The 1-5 scale, based upon wind speeds, tells the potential damage and impact a hurricane can have once it hits land. Since the basis for defining a hurricane on this scale is wind speed, some things such as storm surge and other effects can vary somewhat between categories.
The Saffir-Simpson was first developed in 1969 by civil engineer Herbert Saffir. He realized that unlike earthquakes, there was no common scale used to inform people about the intensity of hurricanes. Initially it was done at the behest of the United Nations who were doing a study of low-cost housing in hurricane prone areas.
After working on this project he gave his new scale to the National Hurricane Center (NHC). The director of the NHC at that time was Bob Simpson. Besides wind speed and potential damage to buildings, Simpson also added the levels of storm surge and flooding to be expected with each of the five categories of hurricanes. The Saffir-Simpson Scale was born.
Tropical Depressions and Tropical Storms
The Saffir-Simpson Scale deals with the five categories of hurricanes. However there are also other distinctions used by hurricane watchers to refer to pre-hurricane storms which they use to monitor developments in possible hurricanes.
The lowest level is a tropical depression. This involves conditions where winds are between 0 and 38 miles per hour. Thestorm surge for a tropical depression is 0 feet.
Somewhat more serious than a tropical depression is a tropical storm. When a depression becomes a tropical storm it is designated with a number. The numbers go up sequentially started at 1 every hurricane season. Tropical storms have wind speeds ranging between 39 and 73 miles per hour, with storm surges ranging between 0 and 3 feet.
Category 1 Hurricane on the Saffir-Simpson Scale
Once a tropical storm hits sustained winds of speeds at 74 miles per hour or more it becomes a Category 1 hurricane. It is at this point that it becomes a named storm (such as Hurricanes Katrina or Rita of the 2005 hurricane season).
Wind speeds for Category 1 hurricanes range between 74 and 95 miles per hour. Storm surge levels range between 4 and 5 feet. This is the weakest type of hurricane, and generally there is no major damage to building structures. Damage that occurs generally occurs to unanchored mobile homes, shrubberies and trees. Some coastal flooding and damage to pier structures is also common.
Examples of Category 1 hurricanes would include Hurricane Ophelia and Hurricane Epsilon in 2005.
Category 2 Hurricane on the Saffir-Simpson Scale
Following Category 1 follows Category 2. Wind speeds here range from 96 to 110 miles per hour. Storm surges range between 6 and 8 feet above normal.
Category 2 storms on the Saffir-Simpson Scale can be expected to do considerable damage to mobile homes and vegetation. Also expect them to damage roofs, windows, street signs and piers. Coastal flooding generally starts beginning 2 to 4 hours before the arrival of the hurricane’s eye.
Hurricane Frances of 2004 and Hurricane Irene of 2005 were both category 2 hurricanes.
Category 3 Hurricane on the Saffir-Simpson Scale
A Category 3 hurricane is marked by sustained wind speeds of between 111 and 130 miles per hour. Storm surges are generally 9-12 feet above normal in a Category 3 hurricane.
Category 3 hurricanes can destroy mobile homes and poorly constructed houses. The storm surges can flood low-lying streets. Flooding can go as far inland as 8 miles, depending on the level of terrain. People living in low-lying areas will most likely need to be evacuated.
Hurricane Katrina of 2005, although it maxed out as a Category 5 hurricane, made landfall in New Orleans as a Category 3. Hurricane Wilma also struck Florida as a Category 3 that year, although it had maxed out as a Category 5 also.
Category 4 Hurricane on the Saffir-Simpson Scale
Category 4 hurricanes are marked by sustained wind speeds of between 131 and 155 miles per hour. Storm surge for Category 4 hurricanes is usually between 13 and 18 feet above normal levels.
Because of high winds, many small trees, shrubs, plants, etc. as well as street signs and other objects can be blown away. Mobile homes and lower quality structures are generally completely destroyed, with significant if not major damage happening to larger and stronger structures. There is a significant chance of flooding in low lying areas less than 10 feet above sea level. Flooding can happen as far as 6 miles inland and evacuation is required in such areas.
Hurricane Dennis in 2005 was a Category 4 when it struck land in Cuba. Hurricane Emly struck the Yucatan Peninsula as a Category 4 in 2005 also.
Category 5 Hurricane on the Saffir-Simpson Scale
Category 5 hurricanes are the strongest hurricanes on the Saffir-Simpson Scale. Any hurricane with winds greater than 155 miles per hour. Storm surges typically exceed 18 feet above normal.
Damage is greatest from a Category 5 hurricane. Complete evacuations of residents less than 15 feet below sea level within 5 to 10 miles of the shoreline will most likely be required. Escape routes can be cut off up to 5 hours prior to the coming of the center of the hurricane, so early evacuation is recommended.
Only 3 Category 5 hurricanes have ever struck land in the US: The Labor Day Hurricane of 1935 which struck Florida (this was before the Saffir-Simpson Scale was put into place), Hurricane Camille in 1969 and Hurricane Andrew in 1992.