Read It's Raining Fish and Spiders Online
Authors: Bill Evans
Hurricane Katrina
NASA
The Saffir-Simpson Hurricane Scale
I'm sure you've heard of hurricanes being rated on some sort of scale. You hear people say, “That storm is a 1,” or “That one is a Category 2,” and so on. Those numbers are from the Saffir-Simpson Scale. This scale was formulated in 1969, after Hurricane Camille slaughtered the Mississippi Gulf Coast. The damage from that hurricane was quite shocking, at least in part because there was, at that time, no way to predict a storm's potential impact. The population had no sense of what to expect from a hurricane of Camille's mammoth strength and size.
National Hurricane Center, National Weather Service, National Oceanic and Atmospheric Administration/Department of Commerce
Dr. Robert Simpson, who at the time was director of the National Hurricane Center in Miami, realized the need to help disaster agencies better understand how much damage a particular storm might cause. So he called on Herbert Saffir, a consulting engineer who, Simpson says, was “well known as the father of the Miami building code.” Simpson handled the meteorology part, and Saffir the engineering part, of developing a new hurricane damage assessment tool.
The two came up with the Saffir-Simpson Damage-Potential Scale, which assigns each hurricane a rating, from 1 to 5, based on the storm's intensity. This scale is used to estimate the potential property damage and flooding expected along the coast from a hurricane landfall. Wind speed is the only determining factor in the scale; after all, projecting storm surge heights are difficult due to the varied slope of the continental shelf and the shape of the coastline in the area where the hurricane makes landfall.
CATEGORY 1 HURRICANE
Winds 74 to 95 mph (64 to 83 kt). This is a minimal hurricane that brings a small storm surge, generally 4 to 5 feet above normal. However, this relatively small surge should not be taken lightly, as the time of the storm's arrival and the shape of the coastline are major factors. For example, if the storm arrives at high tide, then the surge will be higher.
There's little chance of serious damage to buildings in a storm this size. However, there will be some damage to various sorts of structures, especially unanchored mobile homes, and shrubbery and trees, which take a beating. Signs will be blown down as well as some power lines. At the beach or along the coast there will be some flooding of roads and minor damage to piers.
CATEGORY 2 HURRICANE
Winds 96 to 110 mph (83 to 96 kt). This is where you begin to see significant damage to the roofs, doors, and windows of buildings. There's also considerable damage to mobile homes, piers, and to poorly constructed signs on buildings and along roads. The storm surge can be as high as 5 to 10 feet at the normal high tide. Coastal roads and escape routes flood 2 to 4 hours before the arrival of the hurricane's center. Small boats in unprotected anchorages break their moorings and go flying.
CATEGORY 3 HURRICANE
Winds 111 to 130 mph (96 to 113 kt). Once a storm becomes a Category 3, it is considered major. The storm surge is generally 9 to 12 feet above normal with structural damage to residences and other buildings. Mobile homes and most signs are destroyed. Many plants are stripped of their foliage and even large trees are blown down.
Low-lying roads and evacuation routes are cut by rising water 3 to 5 hours before arrival of the center of the hurricane. Flooding near the coast destroys smaller homes and buildings; larger structures are damaged, battered by floating debris. Areas where the land is lower than 5 feet above mean sea level may be flooded for 8 miles or more inland. Residents in these areas will have to be evacuated, especially those within several blocks of the shoreline.
A flooded forest after a storm
Mike Irwin; used by permission.
CATEGORY 4 HURRICANE
Winds 131 to 155 mph (114 to 135 kt). At this point, the storm surge is generally 13 to 18 feet above normal! There's more extensive destruction with some complete roof structure failures on small residences. There's complete destruction of mobile homes and extensive damage to doors and windows of permanent structures. Major damage occurs to lower floors of structures near the shore. Shrubs, trees, and all signs are blown down.
Low-lying escape routes may be cut by rising water 3 to 5 hours before the arrival of the center of the hurricane. Any area of land lower than 10 feet above sea level may be flooded, requiring massive evacuation of residential areas as far inland as 6 miles!
Category 5 Hurricane
Winds greater than 155 mph (135 kt). Whoa! This is the top of the scale! The storm surge is generally greater than 18 feet above normal. Roofs on nearly all residences and industrial buildings will be completely destroyed. Larger structures will be shattered while smaller ones will be blown away. Your mobile home is gone!
There will be severe and extensive window and door damage to inland homes and buildings. There's also major damage to the lower floors of all buildings located less than 15 feet above sea level and within 500 yards of the shoreline. All shrubs, trees, and signs will be blown down.
Low-lying escape routes are cut by rising water 3 to 5 hours before the arrival of the center of the hurricane. There will be massive evacuation of residential areas on low ground within 5 to 10 miles of the shoreline.
Only three Category 5 hurricanes have made landfall in the United States since records began: the Labor Day Hurricane of 1935 (remember, the naming of hurricanes did not begin until the 1940s), Hurricane Camille in 1969, and Hurricane Andrew in August 1992. The 1935 Labor Day Hurricane struck the Florida Keys with a minimum barometric pressure of 892 millibars (mb)âthe lowest pressure of a hurricane at landfall ever observed in the United States. The lower the pressure, the stronger and nastier the storm will be.
When Hurricane Camille struck the Mississippi Gulf Coast, it caused a 25-foot storm surge, which inundated Pass Christian. Hurricane Katrina, a Category 5 storm over the Gulf of Mexico, was responsible for at least 81 billion dollars of property damage when it struck the Gulf Coast as a Category 3. Katrina is by far the costliest hurricane to ever strike the United States.
Hurricane Wilma of 2005 was a Category 5 hurricane at its peak intensity. Wilma is the strongest Atlantic tropical cyclone on record, with a minimum pressure of 882 mb. Fortunately, it did not make landfall at peak intensity! Wilma was a Category 3 as the time of her landfall.
Hurricane Katrina
NASA
Deadliest Tropical Storms in U.S. History, Resulting in Fifty or More Deaths
DEATHS | LOCATION | DATE |
8,000+ | Galveston, T X | September 1900 |
2,500+ | Lake Okeechobee, FL | September 1928 |
1,000â2,500 | SC, GA | August 1893 |
1,800â2,000 | Coastal LA and MS | October 1896 |
1,836 | (Hurricane Katrina) LA, MS | August 2005 |
700+ | GA, SC | August 1881 |
638 | New England | September 1938 |
600+ | Florida (marine) | September 1919 |
500+ | GA, SC | September 1804 |
450+ | Corpus Christi, T X | September 1919 |
424 | NC Capes (marine) | September 1857 |
408 | Florida Keys | September 1935 |
400 | Ãle Dernière, LA | August 1856 |
390 | New England | September 1944 |
390 | (Hurricane Audrey) west LA | June 1957 |
350+ | Grand Isle, LA | September 1909 |
300 | South Carolina | September 1922 |
275 | New Orleans, LA | September 1915 |
275 | Upper coast of Texas | August 1925 |
256 | (Hurricane Camille) MS, V A | August 1 |
243 | Florida | September 1926 |
184 | (Hurricane Diane) NC to ME | September 1955 |
179 | Georgia coast | October 1898 |
176 | Indianola, T X | September 1875 |
164 | Southeast Florida | October 1906 |
134 | FL, AL, and MS | September 1906 |
122 | (Tropical Storm Agnes) PA, NY | June 1972 |
100+ | Sabine, T X | October 1886 |
100 | Florida | September 1896 |
95 | (Hurricane Hazel) NY, NJ | October 1954 |
90+ | SC, NC (marine) | October 1837 |
75 | Hurricane Betsy (FL, LA) | September 1965 |
70 | Brownsville, T X | August 1844 |
68 | Florida | October 1896 |
60 | (Hurricane Carol) MA, ME | August 1954 |
57 | (Hurricane Hugo) SC, NC | September 1989 |
53 | (Hurricane Floyd) NC to NJ | September 1999 |
52 | (Hurricane Ivan) AL, FL | September 2004 |
51 | San Antonio, T X | September 1921 |
51 | Southeast Florida, LA, MS | September 1947 |
50 | South Florida | November 1925 |