Appendixes - Windswept: The Story of Wind and Weather - Marq de Villiers

Windswept: The Story of Wind and Weather - Marq de Villiers (2006)



The composition of the modern atmosphere

The atmosphere contains gases that are considered to be permanent (which remain essentially constant by percent) and gases considered to be variable (which have changing concentrations over a finite period of time).



The Saffir-Simpson hurricane scale

Category 1:

Sustained winds 74-95 mph (64-82 knots). Storm surge generally 4—5 feet 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 2:

Sustained winds of 96-110mph (83-95 knots). Storm surge generally 6-8 feet above normal. Some roofing material, door, and window damage. 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 3:

Sustained winds in-13omph (96-113 knots). Storm surge generally 9-12 feet 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 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 lower than 5 feet above sea level may be flooded inland 8 miles or more. Evacuation of low-lying residences within several blocks of the shoreline may be required.

Category 4:

Sustained winds of 131-155 mph (114-135 knots). Storm surge generally 13-18 feet above normal. More extensive curtainwall failures with some complete roof structure failures on small residences. Shrubs, trees, and all signs 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 feet above sea level may be flooded requiring massive evacuation of residential areas as far inland as 6 miles.

Category 5:

Sustained winds greater than 155 mph (135 knots). Storm surge generally greater than 18 feet 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 feet above sea level and within 500 yards of the shoreline. Massive evacuation of residential areas on low ground within 5-10 miles of the shoreline may be required.


Hurricane strikes in the U S.

U.S. hurricane strikes by decade

U.S. hurricane strikes by state, 1900 through 1996

Major hurricane direct hits on the mainland U.S. coastline from 1900 to 1996, by state and month


Canadian tropical cyclone statistics

Only two major hurricanes (Saffir-Simpson Category 3 or above) have ever made landfall in Canada: an unnamed Category 3 storm in 1893 that made landfall in St. Margaret's Bay, Nova Scotia; and Hurricane Luis, also a Category 3 storm, which made landfall on the Avalon Peninsula, Newfoundland, in 1995.

Hurricane Juan, which hit Nova Scotia and Prince Edward Isand in 2003, was first classified as a Category 1 storm, but it was on the margins of a Category 2, and has been so reclassified.

Note: TS = Tropical Storm; SSi= Saffir-Simpson Category 1 Hurricane; SS2 = Saffir-Simpson Category 2 Hurricane, etc.

* A dash (-) under Pressure means that it was not measured.

Key: NB = New Brunswick NF = Newfoundland NS = Nova Scotia ON = Ontario PEI = Prince Edward Island PQ = Quebec

Most active years of landfalling tropical cyclones in Canada

Year Number

1893 6

1996 5

1995 4

1937 4

1923 4

1891 4

1888 4

1988 3

1979 3

1954 3

Most common date for a landfalling hurricane in Canada

September 15th

Average number of tropical cyclones affecting Canada each year

From 1901 to 2000: 3.3

From 1951 to 2000: 4.2

From 1993 to 2002: 4.9

Source: Canadian Hurricane Centre


World's worst tropical cyclones (hurricanes and typhoons, by year, with casualties)


Wind speed variation within the hurricane eyewall, by elevation


Worst winter storms on record


The Fujita tornado scale

Fujita o, gale tornado:

Winds 40—72 mph. Such tornadoes cause some damage to chimneys, break branches off trees, and push over shallow-rooted trees.

Fujita 1, moderate tornado:

Winds ranging from 74 to 112 mph. The lower limit of a moderate tornado is the sustained wind speed that defines a Category 1 hurricane. Such tornadoes can peel off roofs, overturn mobile homes, and push cars off roads. Some poorly made buildings will be destroyed.

Fujita 2, significant tornado:

Winds ranging from 113 to 157 mph. Such winds will do considerable damage, tearing roofs off many houses, demolishing mobile homes, snapping large trees. "Light-object missiles" will be generated—debris picked up in the winds that become battering rams.

Fujita 3, severe tornado:

Winds from 158 to 206 mph. Roofs and walls torn off well-made buildings, trees uprooted, and even trains overturned.

Fujita 4, devastating tornado:

Winds ranging from 207 to 260 mph. In these conditions even well-made houses are leveled. Structures with weak foundations will be blown some distance. Cars are thrown about, and "large missiles" generated.

Fujita 5, incredible tornado:

Winds of 261 to 318 mph, Strong frame houses lifted off their moorings, car-sized missiles flying about, trees debarked, steel-reinforced concrete badly damaged.

Fujita 6, inconceivable tornado:

Sustained winds of 319 to 379 mph, but no one will ever know, because all measuring devices would be destroyed, along with pretty well everything else. (The Fujita scale recognizes that "the small area of damage they might produce would probably not be recognizable along with the mess produced by F4 and F5 winds that would surround the F6 winds. Missiles, such as cars and refrigerators would do serious secondary damage that could not be directly identified as F6 damage. If this level is ever achieved, evidence for it might only be found in some manner of ground swirl pattern, for it may never be identifiable through engineering studies.")

Source: and the National Severe Storms Laboratory


Worst tornadoes in the twentieth century by year


Wind force table

For a house whose face presents an area of 400 square feet, we can predict the following approximate lateral inertial forces as the wind speed increases:


Canadian wind chill index (in degrees Celsius and wind speeds in kilometers per hour)

Air Temperature

Air Temperature

From -25° to —340: Frostbite likely after prolonged skin exposure to wind

From —350 to —6o°: Frostbite possible in less than 10 minutes

Below -6o°: Frostbite possible in less than 2 minutes