Hurricanes, a destructive force

We call them by their names, this summer: Charley, Frances, Ivan, Jeanne, yet hurricanes are devastating phenomena. Some unleash an equivalent power to several Hiroshima atomic bombs per second. Large-scale natural disasters in worrying succession, hurricanes are causing considerable damage.

The worldwide volume of annual economic loss caused by mind storms has grown from 2 billion USD in the 1960s to 3.4 billion USD in the 1980s, and to 20.2 billion USD in the first three years of the 1990s.
Global warming and climatic disturbances are not the only elements to blame for the rising frequency of these phenomena.


The word cyclone stems from the Greek word kuklos, which means circle. It refers to an atmospheric disturbance originating from the converging and ascending gyratory movement of the wind around a low-pressure area where it has violently been driven from a high-pressure area.

Depression : the source of the hurricane

A big depression caught between two anti-cyclones reinforces wind movements blowing in opposite directions. These winds converge towards the center of the depression. They blow clockwise in the northern hemisphere and otherwise in the southern hemisphere. It is the Coriolis force, triggered by the earth rotation, which is the source of this whirlwind. This force is nil on the equator, hence, the absence cyclonal events in this area.

The cyclone evolution

Initially, a cyclone starts out as a cloudy and rainy mass associated to a low-pressure area. It builds up in high-sea zones where temperatures are above 27°C in depths exceeding 60 meters.
Under the effect of hot humidity (moist), stemming from intensive evaporation, the phenomenon picks up as it sweeps along an unpredictable path. It loses strength in a progressive way as it penetrates inland or when it flies over cold waters.


  • The word cyclone was first used in 1845 by Paddington of the Calcutta observatory. It refers to what used to be called whirlwind or hurricane.
  • The word hurricane is a transliteration of the Hispano-Caribbean word Huracon, and ouragan is nothing else than the frenchfried form of the word.
  • Cyclones in Southern East Asia are called typhoon.


 Photo credit: NASA / Jeff Schmaltz (modified picture) The central ring of the hurricane: the most active zone with torrential rain and violent whirlwinds.
The eye of the cyclone: a forty to a hundred kilometer diameter, lull area with clear sky and light wind.
Eye wall: doline surrounded by 14 000 to 18 000-metre-high cloud ring. It marks the belt of the strongest winds and the heaviest downpours.

Their Christian names

Hurricanes used to have female names. But women lib movements protested and deemed the tradition discriminatory.
Since 1979, hurricanes have had male names in pair years and female names in impair years using six alphabetical lists that are periodically reconducted; a purely formal decision that can in no case change either the lethal power of hurricanes or their itinerary.


Tropical disturbances occur only during the year's hot season when conditions are the most favourable, especially hot moisture which accounts for the cyclone's force. In Australia and Madagascar, the cyclonic season starts from November to April. In the Caribbean and in Florida, the official season of hurricanes extends from June 1 to November 30. Ten to eleven hurricanes have been reported, but since 1995, their frequency has risen to 12 and 14 cyclones per year. Last August, four hurricanes have been registered on the American coasts.

Intensity of tropical disturbances

The evolution of the initial disturbance depends on the regional atmospheric conditions. It can rise from the status of a tropical depression (with wind gusts between 37 and 60 km per hour), to a tropical storm (with wind gusts between 63 to 117 km per hour). Beyond the already-mentioned scales, the initial disturbance builds up to become an intense or very intense tropical cyclone.

The reference used to measure the intensity of disturbances is the Saffir Simpson scale which comprises five grades.

The Saffir Simpson scale
CategoryLabelWind speedEffects
Tropical cyclone118 to 153 km/h (violent wind)
Minor damages: dwellings, trees and some crops
Tropical cyclone154 to 177 km/h (destructive wind)
Significant damages: dwellings, trees. Heavy damages to certain crops, power failure risks.
Intense tropical cyclone178 to 209 km/h (very destructive wind)
Heavy damages to dwellings. Power failures.
Very intense tropical cyclone210 àto249 km/h (very destructive wind)
Considerable damages to infrastructures, destruction of dwellings and crops. Hazardous debris from airlifted objects. Several power stoppages.
Very intense tropical cyclone> 250 km/h (very destructive wind)
Massive destructions of dwellings, infrastructures and crops. Extreme danger from flying debris.

Range and damage

The hurricane's intensity peaks in the eyewall area on a radius of 100 km. Its effects slow down while remaining direct on a 200 km radius. Starting from 400 km, no dangerous effects can be observed.

The damage caused by the passage of a hurricane is of three levels:
  • Violent gusts likely to destroy infrastructures, buildings, vegetations and crops.
  • Heavy downpours resulting in land slide paralysing road and railroad traffic.
  • Successive storms followed by sea water floods resulting from high waves.

Cyclonal areas

Hurricanes grow and pick up in warm oceanic areas where Coriolis force is high. The latter provides the hurricane with its spiral form while maintaining the atmospheric low pressures of the disturbance.

Photo credit: Atlas Magazine
List of the most expensive and murderous hurricanes since 1975
in millions USD
CountryDateEventInsured damages1Victims2
19/04/1976Tropical Cyclone Gorky3138 000
20/11/1977Cyclone in Bengali gulf_10 000
29/08/1979Hurricane Frederic1 899_
25/05/1985Bengal_10 000
Porto Rico, USA
15/09/1989Hurricane Hugo6 20371
05/11/1991Typhoons Thelma and Uring_5 300
27/09/1991Typhoon Mireille7 59851
Bahamas, USA
23/08/1992Hurricane Andrew20 90043
USA , North Pacific
11/09/1992Hurricane Iniki2 0904
03/09/1995Hurricane Luis1 804116
Mexico, USA
01/10/1995Hurricane Opal2 52659
05/09/1996Hurricane Fran1 87039
01/11/1997Typhon Linda63 840
22/10/1998Hurricane Mitch in Central America5629 000
Caraïbes, USA
20/09/1998Hurricane Georges3 969600
10/09/1998Hurricane Gilbert1 694350
India, Bangladesh
29/10/1999Cyclone 05B devastates Orissa State11015 000
22/09/1999Typhoon Bart (south of the country)4 44526
Bahamas, USA
10/09/1999Hurricane Floyd, rains and flood2 59770
USA , Canada
18/09/2003Hurricane Isabel1 68530
02/05/2003Storms, tornado and hail3 20545
South Korea
07/09/2003Typhoon Maemi, gusty wind504131
Florida, USA
13/08/2004Hurricane Charley10 000*117*
Florida, USA
05/09/2004Hurricane Frances5 000*ND
Florida, Alabama
16/09/2004Hurricane Ivan10 000*108*
Haiti, Floride
18/09/2004Hurricane JeanneND2 413*
Table source : Sigma N°1/2004 1 Insured damages: property damages and business interruption, third party damages nor life damages not included 2 Victims: dead and vanished * Provisional estimates NA: not available
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