Tropical cyclones are classified through the Saffir-Simpson Hurricane Wind Scale, which separates hurricane-equivalent storms (tropical cyclones with wind speeds of 64kts or greater) into five separate categories based on wind speed. Anything classified at category 3 or higher is entitled a “major” cyclone.
Note that all damage descriptions listed below do not factor in rainfall, storm surge, tornadoes, and other hazards that tropical cyclones bring, only wind, unless otherwise stated.
Damage: Little to None
A tropical depression is the weakest rating for a tropical cyclone, and most barely qualify as one. Most tropical depressions are strengthening towards tropical storms when they are designated as such. Tropical Depressions do not gain names from official RSMCs. The primary threats with tropical depressions are not winds, but rather heavy rainfall and flooding.
A system becomes a tropical storm once it acquires 1-minute sustained gale force winds. The storm gains a name from the local RSMC once they believe this stage is reached. The wind and storm surge threat increase at this stage, but rainfall remains the biggest threat. Damage is more noticeable, with broken trees and removed roof shingles being the most abundant form of damage with tropical storms. Isolated weak, short-lived tornadoes possible. Power outages are spotty depending on water-related impacts.
“Very dangerous winds will produce some damage”
The storm will now be categorized numerically and be called a hurricane in the North Atlantic and Eastern and Central Pacific, a typhoon in the Western Pacific, and a Cyclone in the Indian Ocean and South Pacific. Weaker trees become uprooted and snapped, but well-built structures usually suffer only minor damage, such as broken windows and scattered roof damage. Coastal erosion from storm surge becomes more severe. Power outages become more widespread and can last days after the storm passes.
“Extremely dangerous winds will cause extensive damage”
Larger and stronger trees may be snapped or uprooted. Sections of roofs may be peeled off of structures. Mobile homes suffer considerable damage, anchored or not. Piers and marinas suffer extensive damage, and boats may be removed from their docks. Power outages become extremely likely and may last for up to a week following the storm. Tap water may be contaminated for days.
“Devastating damage will occur”
The storm is now designated as a “major” cyclone from here on out. Sturdy trees uprooted or snapped, blocking roads. Severe damage to wood-framed structures and buildings without a solid foundation. Whole roofs may be removed from a structure. Storm surge adds to the severe damage along the coast, flooding coastal structures. Power outages are total and may last for weeks. Tap water likely to be contaminated.
“Catastrophic damage will occur”
Mobile homes and smaller, poor foundation buildings are completely destroyed. Potentially irreparable damage to coastal structures and wood-frame homes. Roofs likely to be completely stripped off of well-built structures. Storm surge flooding extends even farther inland, adding to the wind damage. Electricity loss is complete and may last for a month or two. Tap water is undrinkable. The impact zone may be deemed uninhabitable for weeks following the storm.
“Catastrophic damage will occur”
This is the rarest and most significant categorization of the SSHWS. All buildings within 2nmi of the shoreline that are not up to building codes will face almost certain destruction, but all structures will receive some form of damage regardless of how well it is engineered. Complete collapse of the outer parts of well-built structures. Virtually all trees uprooted, some debarked. Storm surge flooding may result in the loss of the lowest level of some structures. Communities deemed unrecognizable. Electricity is completely gone and likely will not return for several months. Tap water is undrinkable. The impact zone may be deemed uninhabitable for months following the storm.
There does not exist a “Category 6” because, once winds approach category 5 strength, the damage to man-made structures becomes complete. After a period as short as 15 seconds of sustained category 5 force winds, then the affected structure will receive some form of damage no matter how well its engineered. Any rating above this would be useless because the structural damage cannot become worse than total, except potentially over a wider area.
For a scale that factors in the other threats that a tropical cyclone brings, please see the “CDPS” section on the website.