The Saffir-Simpson Hurricane Wind Scale rates hurricanes based on their sustained wind speed. On this scale, hurricanes range from Category 1, for sustained wind speeds of 74-95 mph, to Category 5, for sustained wind speeds of 157 mph and higher. This scale is used only in the Atlantic and Eastern Pacific hurricane basins.
The scale was developed by Herbert Saffir and Bob Simpson in 1971. Its original use was to assess the effects of a hurricane on low-cost housing as part of a United Nations commission. At that time, there were no scales which could assess a hurricane's effects.
This early scale ranked hurricanes from 1 to 5, depending on their maximum sustained wind speed, storm surge, and likely flooding. Barometric pressure in the eye was also one of the criteria for ranking.
The Saffir-Simpson scale was unveiled to the public in 1973. It came into widespread public use a year later, after Neil Frank took over from Simpson as Director of the U.S. National Hurricane Center.
Storm surge, flooding, and wind speeds do not always match well with barometric pressure. For example, a large storm with low hurricane-force winds can cause a higher storm surge than a compact storm with high hurricane-force winds.
For this reason, the NHC eliminated pressure, flooding, and storm surge from the Saffir-Simpson scale in 2009. The revised scale was tested for a year before being formally adopted as a pure wind scale on May 15, 2010.
Another small change to the Saffir-Simpson Hurricane Wind Scale took place on May 15, 2012. This change, which expanded the windspeed range for Category 4 hurricanes by 1 mph in both directions, was necessary because the NHC measures hurricane wind speeds in 5-knot increments.
Previously, when knots were converted to mph, the rounding off at either end of the Category 4 range caused those hurricanes to be classified incorrectly as either Category 3 or Category 5. The scale adjustment means that rounding off still keeps hurricanes in their correct categories.
= Category 1 =
Maximum sustained winds are at 74-95 mph. Wind will cause minor damage to roofs and gutters in well-constructed frame houses, with more serious damage in mobile homes and other light housing. These winds can topple electrical poles and uproot shallow-rooted trees. The resulting power outages could last for several days in hard-hit areas.
= Category 2 =
Maximum sustained winds are at 96-110 mph. Wind will cause extensive damage to roofs and siding in well-constructed frame houses, and may completely destroy mobile homes and other light housing. These winds will snap or uproot most shallow-rooted trees. All of the hardest-hit area is likely to lose power for up to several weeks.
= Category 3 =
Maximum sustained winds are at 111-129 mph. Wind will cause major damage to roofs, gables, and siding in well-constructed frame houses, and will completely destroy light structures. Most trees in the hardest-hit areas will be snapped or uprooted. All of the hardest-hit area is likely to lose power. It will be extremely hard to restore electricity and clean water supplies to the hardest-hit areas because of all the other damage. All above-ground utilities could take weeks to restore fully.
= Category 4 =
Maximum sustained winds are at 130-156 mph. Wind will destroy most of the roof structure and some exterior walls in well-constructed frame houses. Lighter structures will be completely destroyed. Most trees in the hardest-hit areas will be snapped or uprooted. All of the hardest-hit area is likely to lose power and clean water. It could take weeks to months before these regions are inhabitable again.
= Category 5 =
Maximum sustained winds are in excess of 157 mph. Many well-constructed frame houses will be completely destroyed, while the rest will have total roof failure and collapsed walls. All of the hardest-hit area will lose power and clean water, possibly for months. It will take at least that long before these regions are inhabitable again.