Saffir-Simpson hurricane scale, index of tropical cyclone intensity that classifies a storm’s wind speed into one of five divisions, or categories. The Saffir-Simpson hurricane scale was developed by American structural engineer Herbert Saffir and American meteorologist Robert H. Simpson (who served as the director of the U.S. National Hurricane Center from 1968 to 1973) in 1971 to help government officials and the public understand the risks posed by an impending tropical cyclone and the amount of property damage and associated impacts that would likely stem from it. The tool was first adopted for use in 1975, and it is the official scale used to classify tropical cyclones occurring in the Atlantic Ocean and northern Pacific Ocean basins east of the International Date Line. Category 1 tropical cyclones are considered the mildest of these types of storms, whereas category 5 tropical cyclones are considered to be the most severe.
Tropical cyclones are classified on the basis of wind speed. Those with winds ranging from 0 to 61 km (0 to 38 miles) per hour are called tropical depressions, whereas those with winds ranging from 63 to 117 km (39 to 73 miles) per hour are called tropical storms. Once a tropical cyclone’s maximum sustained winds at the surface (the highest average wind speeds measured over 1 minute that occur at 10-meter [32.8-foot] elevations over water) reach 119 km (74 miles) per hour, the storm can be ranked on the Saffir-Simpson hurricane scale. In its hurricane forecasting products, the National Oceanic and Atmospheric Administration (NOAA) bundles category 1 and category 2 tropical cyclones together as hurricanes and those of category 3 and above as major hurricanes. (What’s called a hurricane in the North Atlantic and central and eastern North Pacific oceans is typically called a typhoon in the western North Pacific; storms in the South Pacific and Indian oceans, regardless of the strength of their winds, are generally called cyclones.)
| category | wind speed | damage | |
|---|---|---|---|
| mph | km/hr | ||
| *Used to rank tropical cyclones in the North Atlantic Ocean (including the Gulf of Mexico and Caribbean Sea) and the eastern North Pacific Ocean. Published by permission of Herbert Saffir, consulting engineer, Robert Simpson, meteorologist, and the National Weather Service of the National Oceanic and Atmospheric Administration. | |||
| 1 | 74–95 | 119–153 | Very dangerous winds will produce some damage: Well-constructed frame homes could have damage to roof, shingles, vinyl siding and gutters. Large branches of trees will snap and shallowly rooted trees may be toppled. Extensive damage to power lines and poles likely will result in power outages that could last a few to several days. |
| 2 | 96–110 | 154–177 | Extremely dangerous winds will cause extensive damage: Well-constructed frame homes could sustain major roof and siding damage. Many shallowly rooted 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. |
| 3 | 111–129 | 178–208 | Devastating damage will occur: Well-built framed homes may incur major damage or removal of roof decking and gable ends. Many trees will be snapped or uprooted, blocking numerous roads. Electricity and water will be unavailable for several days to weeks after the storm passes. |
| 4 | 130–156 | 209–251 | Catastrophic damage will occur: Well-built framed homes can sustain severe damage with loss of most of the roof structure and/or some exterior walls. Most trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last weeks to possibly months. Most of the area will be uninhabitable for weeks or months. |
| 5 | >157 | >252 | Catastrophic damage will occur: A high percentage of framed homes will be destroyed, with total roof failure and wall collapse. Fallen trees and power poles will isolate residential areas. Power outages will last for weeks to possibly months. Most of the area will be uninhabitable for weeks or months. |
In addition to maximum sustained wind speed, early iterations of the Saffir-Simpson hurricane scale also used the central atmospheric pressure of the storm and storm surge (which raise water levels at the shoreline and inland) to define each category. These measures were removed in 2009 after an internal review by the National Hurricane Center determined that their complexities produced confusion. Although the differences between the atmospheric pressure at the center of the storm and that of the surrounding environment is an important driver of the winds, it was shown that storms could be classified into multiple categories depending upon whether central pressure or wind speed was emphasized. Similarly, storm surge was also removed because its height varied by the depth of the water at the shoreline, surrounding topography, and other geographic factors that the scale could not account for.
As tropical cyclones grew more intense due to the influence of global warming during the 21st century, some meteorologists noticed the limitations of the five-category scale. The category 5 rank does not have an upper limit, and by the 2020s meteorologists had tracked several tropical cyclones whose wind speeds had intensified far beyond the category 5 threshold of 252 km (157 miles) per hour. Such a development has led some scientists to call for an update of the scale, namely to set the upper wind speed limit of a category 5 storm at 307 km (191 miles) per hour and place storms with higher wind speeds into a sixth category.