Akash.RM-Tech(I.C.Z.M)

K.U.F.O.S

"Cyclone" is an intense whirl in the atmosphere with very strong winds circulating around it in anti-clockwise direction in the Northern Hemisphere and in clockwise direction in the Southern Hemisphere.

Word "Cyclone" is derived from the Greek, word "Cyclos" meaning the coils of a snake.

To Henri Peddington, the tropical storms in the Bay of Bengal and in the Arabian Sea appeared like the coiled serpents of the sea and he named these storms as "Cyclones".

known as Hurricane in the Atlantic and Eastem Pacific, Typhoon in Western Pacific, Willy-Willies in Australian sea, Baguis in the Philippines.

Cyclones are intense low pressure areas - from the centre of which pressure increases outwards- The amount of the pressure drop in the centre and the rate at which it increases outwards gives the intensity of the cyclones and the strength of winds. 

As adopted by Meteorological Department of India

S.No. Disturbance Wind Speed (Knots)

1. Low Less than 17.

2. Depression 17-27(32-50 km/h)

3. Deep Depression 28-33 (51-62 km/h)

4. Cyclonic storm 34-47 (63-88 km/h)

5.Severe cyclonic storm with

a core of Hurricane winds

48-63-(89-118 km/h)

1 knot - 1.85 km per hour

A full-grown cyclone is a violent whirl in the atmosphere 150 to 1000 km across, 10 to 15 km high.

The central calm region of the storm is called the "Eye". The diameter of the eye varies between 30 and 50 km and is a region free of clouds and has light winds.

Around this calm and clear eye, there is the "Wall Cloud Region" of the storm about 5O km in extent, where the gale winds, thick clouds with torrential rain, thunder and lightning prevail.

Away from the "Wall Cloud Region", the wind speed gradually decreases.

The gales give rise to a confused sea with waves as high as 20 metres, swells that travel a thousand miles. Torrential rains, occasional thunder and lightning flashes - join these

Through these churned chaotic sea and atmosphere, the cyclone moves 300 to 500 km, in a day to hit or skirt along a coast, bringing with it strome surges

Once the cyclones reach higher latitudes they often change their direction and move north and then north-east (south and south east hemisphere). The process is known as recurreature.

Before it recurves, the speed decreases and the system remains stationary for a day or so.

When two cyclones exist near to each other, they inter-act and move anti-clockwise with respect to each other.

In the Atlantic, tracks often execute a parabola. In India, when cyclones recur they get broken up over the

Himalayas and their further eastward movement ceases.

Cyclones derive their names through a systematic procedure laid down by the World Meteorological Organisation (WMO) and the United Nations Economic and Social Commission for Asia and the Pacific (ESCAP).

naming of cyclones began in September 2004

Eight north Indian Ocean countries - Bangladesh, India, the Maldives, Myanmar, Oman, Pakistan, Sri Lanka and Thailand - have prepared a list of 64 names.

Since 2004, the eight countries have faced 20 cyclones.

The countries take turns in naming the cyclones. The last six were: Nargis (Pakistan), Rashmi (Sri Lanka), Khai-Muk (Thailand), Nisha (Bangladesh), Bijli (India) and Aila (Maldives).

Gales and strong winds damage installations, dwellings, communication systems,

trees., etc. resulting in loss of life and property. Torrential rain

may cause river floods Storm surges or high tidal waves

A storm surge is an abnormal rise of sea level near the coast caused by a severe tropical cyclone

as a result, sea water inundates low lying areas of coastal regions drowning human beings and live- stock, eroding beaches and embankments, destroying vegetation and reducing soil fertility.

Every cyclone that affects the coast produces a storm surge. But not all storm surges rise to dangerous levels. The height of the surge depends on: The intensity of the cyclone - as the winds increase, the sea water is

piled higher and the waves on top of the surge are taller. The forward speed of the cyclone - the faster the cyclone crosses the

coast, the more quickly the surge builds up and the more powerfully it strikes.

The angle at which the cyclone crosses the coast - local zones of enhanced surge in areas such as narrow inlets and bays.

The shape of the sea floor - the surge builds up more strongly if the slope of the sea bed at the coast is shallow.

Past history indicates that loss of life is significant when surge magnitude is 3 metres or more and catastrophic when 5 metres and above

Vulnerability to storm surges is not uniform along Indian coasts. east coast of India are most vulnerable to high surges

i) North Orissa, and West Bengal coasts. ii) Andhra Pradesh coast between Ongole and Machilipatnam. iii) Tamil Nadu coast, south of Nagapatnam.

The West coast of India is less vulnerable to storm surges i) Maharashtra coast, north of Harnai and adjoining south Gujarat

coast and the coastal belt around the Gulf   of  Bombay. ii) The coastal belt around the Gulf of Kutch.

Effective Cyclone Disaster Prevention and Mitigation Plan requires: A Cyclone Forecast - and Warning Service. Rapid dissemination of warnings to the Government

Agencies, Marine interests like the Ports, Fisheries and Shipping and to General Public.

Organisations to construct Cyclone Shelters in the cyclone-prone areas and ready machinery for evacuation of people to safer areas.

Community preparedness at all levels to meet the exigencies.

"Two Stage Warning Scheme“ The first stage warning known as the "Cyclone Alert" is issued

48 hours in advance of the expected commencement of the adverse weather over the coastal areas.

The second stage warning known as the "Cyclone Warning" is issued 24 hours in advance.

Both cyclone "Alert" and "Warning" messages are passed to the AIR stations for repeated broadcast.

Contrary to popular belief, few houses are blown over. Instead, they are pulled apart by winds moving swiftly around and over the building. This lowers the pressure on the outside and creates suction on the walls and roof, effectively causing the equivalent of an explosion.

Whether or not a building will be able to resist the effects of wind is dependent not so much upon the materials that are used but the manner in which they are used.

common belief: that heavier buildings, such as those made of concrete block, are safer.

Truth: well-built and properly-engineered masonry house offers a better margin of safety than other types of buildings

Due to the high wind pressure and improper connection of the house to the footings it can be blown away.

Roofing materials not anchored can be blown away

Light weight verandah roofs are more susceptible to damage due to high wind speed.

When cyclones are accompanied with heavy rain for a long duration, the buildings can be damaged due to flooding also.

Though cyclonic storms always approach from the direction of the sea towards the coast, the wind velocity and direction relative to a building remain random due to the rotating motion of the high velocity winds.

In non-cyclonic region where the predominant strong wind direction is well established, the area behind a mound or a hillock should be preferred

Similarly a row of trees planted upwind will act as a shield. The influence of such a shield will be over a limited distance, only for 8 – 10 times

the height of the trees. A tree broken close to the house may damage the house also hence distance of tree

from the house may be kept 1.5 times the height of the tree.

No shielding from high wind due to absence of barriers

Shielding from high wind by permeable barriers such as strong trees

In hilly regions, construction along ridges should be avoided since

they experience an increase of wind velocity whereas valley experiences lower speeds in general

In cyclonic regions close to the coast, a site above the likely inundation level should be chosen. In case of non availability of high level natural ground, construction should be done on stilts with no masonry or cross bracings up to maximum surge level, or on raised earthen mounds to avoid flooding/inundation but knee bracing may be used.

Shape is the most important single factor in determining the performance of buildings in cyclones.

Simple, compact, symmetrical shapes are best. The square plan is better than the rectangle since it allows high

winds to go around them. The rectangle is better than the L-shaped plan. This is not to say that all buildings must be square. But it is to say

that one must be aware of the implications of design decisions and take appropriate action to counter negative features.

The best shape to resist high winds is a square.

If other shapes are desired, efforts should be made to strengthen the corners.If longer shapes are used, they must be designed to withstand the forces of the wind. Most houses are rectangular and the best layout is when the length is not more than three (3) times the width.

In case of construction of group of buildings, a cluster arrangement can be followed in preference to row type.

Lightweight flat roofs are easily blown off in high winds.

In order to lessen the effect of the uplifting forces on the roof, the roof Pitch should not be less than 22º.

Hip roofs are best

General Design Considerations Avoid a low pitched roof, use a hip roof or a high

pitched gable roof. Avoid overhanging roofs. If overhangs or canopies

are desired, they should be braced by ties held to the main structures.

Avoid openings which cannot be securely closed during a cyclone

The foundation is the part of the house which transfers the weight of the building to the ground. It is essential to construct a suitable foundation for a house as the stability of a building depends primarily on its foundation.

It is desirable that information about soil type be obtained and estimates of safe bearing capacity

Effect of surge or flooding:- Invariably a cyclonic storm is accompanied by torrential rain and tidal

surge (in coastal areas) resulting into flooding of the low lying areas. Flooding causes saturation of soil and thus significantly affects the safe

bearing capacity of the soil. In flood prone areas, the safe bearing capacity should be taken as half

of that for the dry ground. Also the likelihood of any scour due to receding tidal surge needs to

be taken into account while deciding on the depth of foundation Buildings on stilts:-

Where a building is constructed on stilts it is necessary that stilts are properly braced in both the principal directions.

Knee bracings will be preferable to full diagonal bracing so as not to obstruct the passage of floating debris during storm surge.

Before the Cyclone season: Check the house; secure loose tiles, carry out repair works for

doors and windows Remove dead woods or dying trees close to the house; anchor

removable objects like lumber piles, loose tin sheds, loose bricks, garbage cans, sign-boards etc. which can fly in strong winds

Keep some wooden boards ready so that glass windows can be boarded if needed

Demolish condemned buildings Keep some dry non-perishable food always ready for

emergency use

When the Cyclone starts Listen to the radio about weather warnings Pass on the information to others. Believe in the official information Remember that a cyclone alert means that the danger is within 24 hours.

Stay alert. If your house is securely built on high ground take shelter in the safer part

of the house. However, if asked to evacuate do not hesitate to leave the place.

Provide strong suitable support for outside doors. Keep torches handy Be sure that a window and door can be opened only on the side opposite to

the one facing the wind. If the centre of the cyclone is passing directly over your house there will be

a lull in the wind and rain lasting for half and hour or so. During this time do not go out; because immediately after that very strong winds will blow from the opposite direction.

Switch off electrical mains in your house. Remain calm

When Evacuation is instructed Pack essentials for yourself and your family to last you a few

days, including medicines, special foods for babies and children or elders.

Head for the proper shelter or evacuation points indicated for your area.

Do not worry about your property At the shelter follow instructions of the person in charge. Remain in the shelter until you have been informed to leave

Post-cyclone measures You should remain in the shelter until informed that

you can return to your home. Strictly avoid any loose and dangling wires from the

lamp posts. Clear debris from your premises immediately. Report the correct loss to appropriate authorities

http://www.emergency.qld.gov.au/emq/css/cyclone.asp

http://www.ema.gov.au/www/ema/schools.nsf/Page/GetTheFacts_Cyclones_Cyclones?open&query=Cyclones

http://www.bom.gov.au/nsw/sevwx/facts/ecl.shtml