In the Atlantic, hurricane intensity is often classified based on maximum surface wind speed using the five categories of the Saffir-Simpson Hurricane Wind Scale, where categories 3-5 are considered major hurricanes:
Category: 1 Wind (km/h): 119-153 Wind (mph): 75-95
Description: 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..
Category: 2 Wind (km/h): 154-177 Wind (mph): 96-110
Description: 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.
Category: 3 Wind (km/h): 178-208 Wind (mph): 111-129
Description: 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.
Category: 4 Wind (km/h): 209-251 Wind (mph): 130-156
Description: 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.
Category: 5 Wind (km/h): 252+ Wind (mph): 157+
Description: 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 general, damage from landfalling hurricanes increases roughly 4 times for each category they intensify. However, lower category storms (and tropical storms) can cause substantial damage depending on their size, the other weather features with which they interact, where they strike, and the speed with which they propagate. In addition to wind, damage from hurricanes also depends on storm surge (which can cause coastal flooding) and rainfall-induced inland flooding. Storm surge is as much a function of storm size (hurricane force wind radii) as it is the peak winds of a hurricane.