Hurricanes are a major threat to both life and property for those living in coastal areas. However, to understand just how threatening a storm is, you must understand the scale on which they are rated.
In the Atlantic and Eastern Pacific Oceans, hurricanes are rated on what is known as the Saffir-Simpson Hurricane Scale, developed by civil engineer Herbert Saffir and meteorologist Bob Simpson in the early 1970s. Different tropical storms are rated on this scale by meteorologists at the National Hurricane Center in Miami, Florida.
This scale is relatively simple, and it is used to gauge the overall intensity of a hurricane based on sustained wind speed. The Saffir-Simpson scale defines sustained wind speed as winds persisting at a certain speed or greater for at least one continuous minute.
So for example, if a hurricane has 100 mph sustained winds, that means that the surface wind speed in the strongest portion of the storm reaches 100 mph or greater for at least one minute. There could also be some lulls or some stronger gusts.
That being said, the scale begins with the weakest tropical system: the tropical depression. A depression is a relatively unorganized area of disturbed weather in the tropics with sustained winds below 39 mph. It is generally not a big threat for any area that it impacts, and any damage will be extremely minor.
However, once the winds exceed 39 mph, the storm will be upgraded to a tropical storm. Tropical storms are slightly more organized, and they can bring a small amount of storm surge.
Storm surge is caused by strong winds pushing water onto the shore, raising the overall sea level and causing flooding. In a tropical storm, this surge can reach up to 3 feet over the regular tidal level, enough to cause minor coastal flooding.
The more destructive surge will arrive in more powerful tropical cyclones with winds greater than 74 mph, what we know as hurricanes. The Saffir-Simpson scale divides hurricanes into 5 different levels of intensity, known as categories.
The lowest level, Category 1, brings sustained winds ranging from 74 to 95 mph and storm surge of 4 to 5 feet. This can be enough to cause some minor structural damage to mobile homes and poorly constructed buildings. Trees may also be uprooted and toppled.
Next up is a Category 2 storm with winds between 96 and 110 mph. Surge can reach from six to eight feet. This can cause more significant damage to mobile homes, as well as blow out some windows and doors. Boats may also break loose from their moorings due to the surge and heavy waves.
At Category 3, a hurricane is officially termed a “Major Hurricane” by the Saffir-Simpson scale. Sustained winds in these storms can be anywhere between 111 and 130 mph. Storm surge will average around 9 to 12 feet. The strength of this storm is enough to damage well-built structures, but it can almost completely destroy poorly-built ones. Mobile homes will be obliterated, and flooding will be severe.
Stronger than a Category 3 storm is the Category 4 hurricane. In one of these storms, winds range from 131 to 155 mph. Storm surge can be between 13 and 18 feet above normal levels. Damage in these storms is usually severe, with major structural damage to most buildings. Weaker structures may be totally wiped out.
The strongest type of hurricane on the Saffir-Simpson scale is a Category 5 storm. These monster hurricanes pack winds greater than 156 mph and surge exceeding 18 feet. If one of these makes landfall, the damage will be catastrophic, with only the strongest of all structures surviving. All others will likely be completely leveled. Some buildings may be completely washed away by the surge.
Fortunately however, Category 5 hurricane landfalls are exceedingly rare. The only three recorded in United States history were the Labor Day Hurricane of 1935, which hit the Florida Keys, Hurricane Camille in 1969, which made landfall in Louisiana, and Hurricane Andrew in 1992, which hit near Miami, Florida. All three of those storms caused severe and lasting damage.
It is important to note however that a storm does not need to be a Category 5 to cause death and destruction, so it is crucial that you heed any and all evacuation warnings for your area in the event of a tropical storm or hurricane.