Classification

Tropical cyclones are classified in different ways in different basins. The Saffir-Simpson Hurricane Wind Scale is the primary classification method for TCs, developed by Herbert Saffir and Robert Simpson in 1971. It was introduced to the public 2 years later and has been in place ever since for basins in the NHC and CPHC areas of responsibility. Some basins use their own scales, specifically the Western Pacific, North Indian, and all Southern Hemisphere basins, but they are generally similar to the Saffir-Simpson scale.

How does the SSHWS Work?

The SSHWS rates TCs based on their 1-minute maximum sustained wind speed. Categorization begins once a TC becomes a hurricane, or a hurricane-equivalent storm. It rates hurricanes from category 1 to 5, with category 5 being the highest and rarest classification. Below category 1, tropical depression and tropical storm classifications are used. Any storm of category 3 status or greater is classified as a major hurricane. These classifications give a general idea of what damage is to be expected from the TC. However, the scale only incorporates wind speeds, and not rainfall or storm surge, factors that are responsible for the majority of hurricane-related damages and deaths. As a result, damage levels indicated below are based solely on wind and not rainfall or storm surge.

Categories

Below, you will find designation of a tropical cyclone with an image of a typical storm of that category, the wind speeds, and the typical damage found with them. Note that tropical depressions and storms are not officially classified under the SSHWS.

Tropical Depression 08L moving ashore north of Tampico, Mexico, on Sept. 6, 2013. (MODIS)

Tropical Depression:
Winds: <33kts (<38mph)
Typical Damage: Minimal
Tropical Depressions are designated when an invest acquires a closed circulation and characteristics associated with tropical systems; therefore, they are barely tropical cyclones, so the wind threat associated with them is minimal. However, isolated tree damage is not unheard of with these systems. Rainfall is by far the biggest threat with tropical depressions, and depending on movement, they can drop extreme rains over a short period of time, which can result in significant flash flooding.

Tropical Storm Edouard south of Louisiana on Aug. 6, 2008. (MODIS)

Tropical Storm:
Winds: 34-63kts (39-73mph)
Typical Damage: Light
Tropical Storms impacting land contain higher winds than depressions, as they are generally better developed. Winds are still not the main threat with tropical storms, but they can be damaging. Scattered damage to trees and even power-lines are possible with these winds, which can result in some structural damage or loss of electricity for a period of time, most likely no longer than day. Coastal flooding from storm surge also becomes a danger with tropical storms, although overall impacts from it is relatively minor. Rainfall remains the most hazardous threat with tropical storms, as they can dump high amounts of rain over short periods of time in some areas, which, similarly with tropical depressions, can cause flash flooding.

Hurricane Hermine approaching the Big Bend region of Florida on Sep. 1, 2016. (Suomi NPP)

Category 1 Hurricane:
Winds: 64-82kts (74-95mph)
Typical Damage: Moderate
Even though they are the least intense type of hurricane, category 1 hurricanes can still produce widespread and life-threatening impacts. They usually cause little structural damage to most well-constructed permanent structures, but they can topple unanchored mobile homes. They can uproot or snap weak trees, and roof shingles or tiles may even blow off towards the upper end of the wind range. Power outages are typically widespread and can last a couple of days. Coastal flooding from storm surge may cause pier and marina damage as well as minor beach erosion. Rainfall totals are heavily dependent on forward motion from here on out, so a slow-moving storm would drop more rain than one moving more quickly.

Hurricane Isabel approaching landfall in North Carolina on Sept. 18, 2003. (MODIS)

Category 2 Hurricane:
Winds: 83-95kts
Typical Damage: Considerable
Category 2 hurricanes often damage roofing material and inflict damage upon poorly constructed door frames and windows. Badly supported signs can receive considerable damage, and many trees are uprooted or snapped, depending on the strength of the tree. Mobile homes are either severely damaged or destroyed, and many manufactured homes also suffer some form of structural damage. Most, if not nearly all, customers are left without power, which may not be restored for up to a week following the hurricane. Storm surge may cause small craft in unprotected anchorages to break from their moorings and cause major damage to piers and marinas. Structures further inland may experience severe damage from storm surge.

Hurricane Otto approaching landfall in southern Nicaragua on Nov. 24, 2016 (MODIS)

Category 3 Hurricane:
Winds: 96-112kts (111-129mph)
Damage: Extensive
For the Atlantic or Eastern Pacific basins, storms of category 3 strength or greater are classified as major hurricanes. Category 3s can cause severe structural damage to small residences and utility buildings, especially to those of wood frame or weaker manufactured materials. Manufactured homes usually sustain high damage, which can sometimes cause it to become irreparable. Buildings that lack a solid foundation, such as mobile homes, are destroyed, and parts of roofs are peeled off. Large, deep-rooted trees can be snapped or uprooted, which can block roads and isolate many areas. Near-total power loss is expected for up to several weeks and water will likely also be contaminated for a short time. Storm surge flooding near the coast can destroy smaller structures, while larger structures may be struck by floating debris. Marinas and docks may be destroyed by storm surge flooding, and many boats may be washed inland or taken out to sea.

Hurricane Wilma lumbering towards Cozumel on Oct. 21, 2005. (MODIS)

Category 4 Hurricane:
Winds: 113-136kts (130-156mph)
Damage: Catastrophic
Category 4 hurricanes produce more extensive structural failures, with complete failure on smaller buildings. Roof damage is rampant and sometimes complete, and some exterior walls are destroyed. Heavy, often irreparable, damage and near complete destruction of gas station canopies and other overhanging structures are common. Mobile and manufactured homes are completely leveled. Most trees, except for the sturdiest, are uprooted, snapped or even debarked, blocking roads and isolating many areas. Extensive beach erosion is to be expected and the terrain may be flooded far inland from storm surge. Coastal structures either suffer severe damage or are destroyed. Total and long-lived electrical and water losses are to be expected. Most of the area impacted will be uninhabitable for weeks.

Hurricane Irma barreling towards the northern Leeward Islands on Sep. 5, 2017 (Suomi NPP)

Category 5 Hurricane:
Winds: >137kts (>157mph)
Damage: Cataclysmic
Category 5s produce the most extreme damage from hurricanes, consisting of near-total and complete destruction. These storms cause complete roof failure on many residences and industrial buildings, and most buildings suffer complete structural failure. Smaller utility buildings are blown away off their foundations. Collapse of many wide-span roofs and walls, especially those with no interior supports, is almost guaranteed. Wood frame structures suffer extreme and likely irreparable damage. Only a few types of structures are capable of surviving intact, but likely only if located at least 4mi inland, depending on terrain. These include any building with a solid concrete or steel frame construction or those with a brick or concrete/cement blocks that have little slope to their roofs. If the windows are made of hurricane-resistant safety glass or are covered with sturdy shutters, then the structure will have a better chance of survival. If the building does not meet these requirements, then complete destruction of a structure is certain. Storm surge inundation reshapes the coastline and floods inland for multiple miles. Power loss is complete and the water supply will likely be contaminated for several months to possibly as much as a year. The region will remain uninhabitable for months following the storm.

Why no “Category 6”?

After the series of devastating and powerful hurricanes in the 2005 and 2017 Atlantic hurricane seasons, some were calling for an additional category, the alleged “Category 6”, to be added to the SSHWS. The scale is based of damage potential, and past the total damage that category 5s bring, there is not much more that can be done, except perhaps extending the area of complete damage over a wider area. The reason that the scale stops at category 5 is that once winds exceed 140kts, it’s likely that there will be total damage throughout the impact zone. Any building, regardless of how well it’s engineered, will sustain some form of structural damage after just six seconds of exposure to winds of category 5 strength. If every structure maintained some form of structural damage, then the damage can be qualified as “total”.

Below is a visualization of damage typical with its associated SSHWS category on a beachfront property. Note that these storm surge values are not always the same with every storm in a certain category, as storm surge heights are also dependent on other factors, such as storm size and movement.

Visualization of typical damage associated with each SSHWS category on a beachfront home. (Press Association)