Cyclones ahead - Be prepared

by K. R. Abhayasingha, Former Director of Meteorology

It is not too long after the second inter-monsoon, 2006 which recorded tremendous amount of weather-related natural hazards in Sri Lanka. With the beginning of the second inter monsoon season in the second week of October, 2006 the country experienced the typical hazardous weather conditions.

Torrential rain and lightning associated with thunderstorms ended up with a calamity; death and property damage.

Weather-related natural hazards are recurrent yearly as the seasonal climate patterns repeat every year.

We are reaching the last quarter of the year 2007. The rains fell so far (May-Mid August) during the Southwest Monsoon season seems to be lower than the average for the relevant period. But even with such weather situation natural hazards were reported from a number of places.

Evolution of the earth has been undergoing long processes through billions of years and there is no reliable proof yet to witness the completion of the evolution. As it happened yesterday, is happening today the evolution will continue in future.

This is common to any location or any country on the globe and as a result, many parameters including those related to weather and weather systems are continuously changing and fluctuating.

In addition to the natural changes, the influences of the cruel human activities have added significant changes to the global temperature and the climate. Global warming has already resulted in changes of climate and increase of intensity and frequency of extreme weather events like cyclones, Warm climate conditions, snowstorms, thunderstorms, tornadoes and El Nino.

The large number of cyclones developed in 2005 in the Pacific and severe cyclones which caused significant hazards in a number of parts of the world in 2006 and 2007 signals us about the bad results of the global warming.

Meteorologists have already warned the world of development of severe cyclones in the Pacific Ocean in coming cyclone season. Unfortunately no one has so far disclosed the weather in the Bay of Bengal in coming months. But we are to revise our own understanding of the weather systems that influence weather in Sri Lanka during the second inter monsoon season and early part of the North east monsoon.

Statistics has shown us that this is the period with high probability of cyclones in the Bay of Bengal.

Changes of weather parameters and the extreme events were there from the beginning of our atmosphere and they are not new. Droughts, floods, warm climate episodes, cold episodes, cyclones, snowstorms, tornadoes and lightning have been common and natural events on the globe in different scales in different parts of the world in different seasons throughout the history.

Fluctuations of weather, climate and extreme weather events have also affected the globe during the history.

As there are clear evidences of global warming and climate change during last few decades, the environmental scientists and meteorologists are organizing all types of awareness programs to bring the message of the rising trend of frequency and the intensity of hazardous weather systems as a result of unusual warming of the globe.

It is the right of all nations to understand the real situation and also the normal climate and weather conditions in climate seasons leading to natural hazards. Such understanding is required in order to mitigate those natural hazards.

Climate change is certainly not responsible for all observed developments of extreme weather systems and their fluctuations. There are many occasions with extreme weather situations occurring under normal environmental circumstances. Significant changes of climatic parameters in all time scales are normal and natural for any place or any country on our earth.

Weather conditions expected during the coming second Inter monsoon season and the early part of the North East Monsoon include thunderstorms, tornadoes, low level disturbances, depressions and cyclones.

Therefore we should be prepared for all the effects, preferably the bad effects, of them. There are a number of precautionary steps that help to, reduce or mitigate the possible Natural Disasters.

Cyclones are hazardous and they have been responsible for considerable damage to property and life in the world and our country as well. The severe cyclones that swept many parts of Sri Lanka in November 1978 and December 2000 are good examples.

These systems have enormous energy, more powerful than an atomic bomb, and hazards are caused in a number of ways by strong winds, heavy rains, storm surges and lightning.

The paths of the cyclones also show peculiar characteristics. The cyclonic systems developing in the Northern Hemisphere move initially in a westerly to northwesterly direction while aging and tend to re-curve towards northeast.

For this reason, meteorologists in the region, particularly those in India and Sri Lanka, show a special interest to watch the cyclones that develop in the Bay of Bengal because they move towards us while intensification. Many parts of the Indian ocean have high probability of giving birth to the low-pressure areas but only those develop in the Bay of Bengal considerably influence (direct or indirect) on weather over Sri Lanka.

Diameter of a well intensified cyclone is in the order of 1000 kilometres (km) but the dimensions of the area affected by such a system may be very much larger than 1000 km. Cloudy skies with fairly strong winds, gusty at times, and continuous rain or thundershowers are the normal weather conditions that prevail over many parts of the country when we are under the influence of a cyclones centred over, or in the vicinity of, Sri Lanka.

Coastal areas are affected by the storm surges, which are caused by the interaction of the winds associated with a cyclone and the surface water of the ocean. This interaction will increase the wave heights to values of about 5 - 6 meters and such waves cross the coast into the land. It is obvious that such waves will wash the property on the coastal regions away to the sea on their way back.

When a cyclone is close to the island, say about 500km from eastern coast, it may show significant influence on weather parameters like wind and rain over the island and on waves over the adjoining sea area causing surges.

Under such situations, fishermen are warned to refrain from going to the seawaters for fishing. With the movement of such a system towards the island the intensity of the hazardous effects will definitely increase and all under the threat have to take all possible protection and precaution in order to reduce hazards.

The eastern parts of the island are the most vulnerable to cyclones that cross over or pass close our island because the strongest winds and storm surges influence directly the eastern coastal areas. But depending on the intensity of a cyclone and its position, other coastal areas also may have effects of storm surges.

Many low-lying areas are directly affected by strong winds, heavy rains and lightning and indirectly by floods. Those living in hilly areas have to face the hazards caused by small-scale or large-scale landslides and damages caused by fallen and uprooted huge trees. Therefore, we should launch the precautionary steps to minimize the loss of life and damage to property well in time.

It is our duty to take all precautionary measures that can be taken before such an event in order to reduce and/or minimize hazards. Also we have to be ready for cyclones and get organised to launch all necessary steps to reduce hazards during and after a cyclone.

Since natural weather events cannot be stopped or avoided, we have nothing other than considering and practising precautionary steps to mitigate the hazards.

Winds, particularly strong and gusty wind streams, are associated with low level disturbance, depressions, cyclones, thunderstorms and tornadoes. Winds are capable in lifting and blowing off the roots of buildings and braking and uprooting trees.

Fallen trees and their branches are responsible for most of the tornado damages. Simple remedy is cutting the branches of vulnerable trees and cutting or trimming the inclined and old trees to make them resistive to strong blowing.

This is important matter to be thought seriously as the trees around and close by buildings (preferably houses) are concerned. It is important to note that such precautions should be and can be successfully launched in fair weather days.

Sheet-roofs (asbestos and aluminium) have to be protected. This can be done by clipping the sheets, bonding them properly and/or tying them tightly with strong and heavy parts of buildings.

Hazards caused by rains

Rain has direct and indirect effects. Soil erosion, collapse of low-grade buildings and damage to crops, particularly those in agricultural sites, and mild earthslips are common direct effects of heavy rains. Improper irrigation systems and blocking of canals in both rural and urban areas have been already understood as main reasons for this. Therefore the precautionary steps are obvious, and the remedial steps have to be thought of during the fair weather periods.

Floods, landslides, epidemics are indirect or after effects of the heavy and intermittent rains. Individuals and the relevant authorities are aware of the types of precautionary steps of which majority of them should be performed during the fair weather periods.

Hazards caused by tornadoes

Tornadoes, also products of Cumulonimbus clouds, are responsible for a bigger percentage of the physical damages resulted by thunderstorms in cyclones.

Thunderstorms with vigorous up draft and spinning winds are capable of giving birth to tornadoes. The ultimate stage of concentration of both cyclonic spin and energy of atmospheric motion is reached in the tornado.

If the air is particularly humid, water vapour may condense in the core and a funnel cloud then projects down from the main cloud base.

Fresh energy is released by this condensation and the cloud may then extend to ground level to form the tornado; the cloud column is usually twisted hence the name 'twister' sometimes given to the phenomenon. The intense twisters suck up small objects like dust, leaves and debris and therefore, the twister or the funnel is seen from distant places like a dark column stretching towards the ground.

Tornadoes average about 100 metres across. Their destructive power is caused both by their tremendous winds, which may exceed 200kt (400 kmph), and by the great radial gradient of pressure, which causes explosive destruction of buildings etc., in their path. Their duration is very variable, about 10 to 15 min on average.

The life of a tornado is as short as 10-15 min. During this time it moves very fast, does the damage and dissipates. Therefore those who have a close threat of a tornado should have to take precautions very quickly in order to minimize the tornado-caused hazards. Tornadoes are common during the inter-monsoon periods (March - April and October - November). But their development under any circumstances with unstable atmosphere during any season cannot be ruled out.

A number of tornadoes may be embedded within a cyclonic system too. We have had enough natural hazards in the past and causes of such hazards are well understood. Therefore it is not genius thing to spend money and time unnecessarily to analyze the causes of the natural hazards and write research papers and lengthy articles to media after each event.

We have enough experience of fatal hazards of extreme weather events experienced in the past. And it is dead sure that the events will develop and affect our country in future too. What we have to do is taking all precautionary steps in time to get prepared for the disasters.