The Saffir-Simpson Hurricane Scale
Category 1 – 74-95 mph (64-82 knots; 119-153 km/hr). Damage is limited to foliage, signage, unanchored boats and mobile homes. There is no significant damage to buildings. The main threat to life and property may be flooding from heavy rains.
Category 2 – 96-110 mph (83-95 knots; 154-177 km/hr). Roof damage to buildings. Doors and windows damaged. Mobile homes severely damaged. Piers damaged by storm surge. Some trees blown down, more extensive limb damage.
Category 3 – 111-130 mph (96-113 knots; 178-209 km/hr). This is the first step of Major Hurricane. Landfalling major hurricanes have their names retired from the list of available hurricane names. For example, after Hurricane Charley made landfall in Florida as a Category 4 hurricane, its name was retired. In the future, when someone says “Hurricane Charley”, there will be no doubt which storm is meant. Category 3 storms cause structural damage to some buildings. Mobile homes are completely destroyed. Roof damage is common. Storm surge begins to cause significant damage in beaches and harbors, with small buildings destroyed.
Category 4 – 131-155 mph (114-135 knots; 210-249 km/hr). Structural failure of some buildings. Complete roof failures on many buildings. Extreme storm surge damage and flooding. Severe coastal erosion, with permanent changes to the coastal landscape not unheard of. Hurricane force winds extend well inland.
Category 5 – Greater than 155 mph (135 knots; 249 km/hr). Complete roof failure on most buildings. Many buildings destroyed, or structurally damaged beyond repair. Catastrophic storm surge damage. All Category 5 hurricanes’ names are retired, regardless whether they ever make landfall. In the Northwest Pacific, a typhoon that reaches 150 mph (241 km/hr) is called a Super Typhoon. The damage caused by a super typhoon is equivalent to a strong Category 4 or Category 5 hurricane, depending on how strong the typhoon is. Because conditions in the Northwest Pacific favor storm formation throughout most of the year, super typhoons are much more common than Category 5 hurricanes. Every year the Northwest Pacific sees several super typhoons, while the Atlantic might see one Category 5 every few years.
A note on storm surge: Historically, storm surge is the primary killer in hurricanes. The Saffir-Simpson scale above gives an approximation of storm surge height; however, the exact storm surge in any given area will be determined by how quickly the water depth increases offshore. In deep-water enviroments, such as the Hawaiian islands, storm surge will be enhanced by the rapidly decreasing ocean depth as the wind-driven surge approaches the coast. The storm surge is on the right-front quadrant (left-front in the Southern Hemisphere) of the eyewall at landfall, where on-shore winds are the strongest. Contrary to a popular myth, the storm surge is entirely wind-driven water—it is not caused by the low pressure of the eye. Another factor in the severity of the storm surge is tide. Obviously, an 18-foot storm surge at high tide is that much worse than an 18-foot surge at low tide.
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