The Saffir-Simpson Hurricane Scale is a 1—5 rating based on the hurricane’s present intensity. This is used to give an estimate of the potential property damage and flooding expected along the coast from a hurricane landfall. Wind speed is the determining factor in the scale, as storm surge values are highly dependent on the slope of the continental shelf and the shape of the coastline, in the landfall region. Note that all winds are using the U.S. 1-minute average.
Category One Hurricane: Winds 74–95 mph (64–82 kt or 119—153 km/hr). Storm surge generally 4—5 ft above normal. No real damage to building structures. Damage primarily to unanchored mobile homes, shrubbery, and trees. Some damage to poorly constructed signs. Also, some coastal road flooding and minor pier damage.
Category Two Hurricane: Winds 96–110 mph (83–95 kt or 154–177 km/hr). Storm surge generally 6–8 feet above normal. Some roofing material, door, and window damage of buildings. Considerable damage to shrubbery and trees with some trees blown down. Considerable damage to mobile homes, poorly constructed signs, and piers. Coastal and low-lying escape routes flood 2–4 hours before arrival of the hurricane center. Small craft in unprotected anchorages break moorings.
Category Three Hurricane: Winds 111–130 mph (96–113 kt or 178–209 km/hr). Storm surge generally 9–12 ft above normal. Some structural damage to small residences and utility buildings with a minor amount of curtainwall failures. Damage to shrubbery and trees with foliage blown off trees and large trees blown down. Mobile homes and poorly constructed signs are destroyed. Low-lying escape routes are cut by rising water 3–5 hours before arrival of the center of the hurricane. Flooding near the coast destroys smaller structures with larger structures damaged by battering from floating debris. Terrain continuously lower than 5 ft above mean sea level may be flooded inland 8 miles (13 km) or more. Evacuation of low-lying residences with several blocks of the shoreline may be required.
Category Four Hurricane: Winds 131–155 mph (114–135 kt or 210–249 km/hr). Storm surge generally 13–18 ft above normal. More extensive curtainwall failures with some complete roof structure failures on small residences. Shrubs, trees, and all signs are blown down. Complete destruction of mobile homes. Extensive damage to doors and windows. Low-lying escape routes may be cut by rising water 3–5 hours before arrival of the center of the hurricane. Major damage to lower floors of structures near the shore. Terrain lower than 10 ft above sea level may be flooded requiring massive evacuation of residential areas as far inland as 6 miles (10 km).
Category Five Hurricane: Winds greater than 155 mph (135 kt or 249 km/hr). Storm surge generally greater than 18 ft above normal. Complete roof failure on many residences and industrial buildings. Some complete building failures with small utility buildings blown over or away. All shrubs, trees, and signs blown down. Complete destruction of mobile homes. Severe and extensive window and door damage. Low-lying escape routes are cut by rising water 3–5 hours before arrival of the center of the hurricane. Major damage to lower floors of all structures located less than 15 ft above sea level and within 500 yards of the shoreline. Massive evacuation of residential areas on low ground within 5–10 miles (8–16 km) of the shoreline may be required.
Source: National Hurricane Center; Shortened Version.
Note on Units of Measurement: In addition to the wind-speed measurements that are so critical to determining a hurricane’s Saffir-Simpson rating—and which in this book are expressed in the familiar “miles per hour”—several other units of measurement are also employed throughout this text and merit some further explication here.
I have often found the need to discuss atmospheric pressure, or, more specifically, minimum central pressure (or minimum sea-level pressure) estimates in hurricanes. Atmospheric pressure is simply the force exerted by the weight of air molecules over a particular area. To express pressure, I have followed the practice of U.S. National Hurricane Center public advisories and used “millibars” (mb) as well as “inches” (in), the latter being short for “inches of mercury.” A conversion from millibars to inches of mercury can be achieved by multiplying millibars by .02953. Thus, a hurricane whose minimum central pressure in millibars is 902 would have a minimum central pressure in inches of mercury of 26.64, rounded to two decimal places (902 × .02953 = 26.64).
I have also often found the need to discuss temperatures, most frequently at the sea surface. Here, following the United Nations’ Intergovernmental Panel on Climate Change (and for general convenience and simplicity), I have used degrees Celsius rather than degrees Fahrenheit or some other unit of measurement (although I have occasionally provided a Fahrenheit conversion in the text as well). A conversion from Celsius to Fahrenheit can be achieved by multiplying a Celsius measurement by 1.8 and then adding 32. Thus, if sea-surface temperatures are 30 degrees C, they are 86 degrees Fahrenheit; [(30 × 1.8) + 32] = 86.