Tropical Cyclones & IMD Warning (Part-2)

1. What are the pre-cyclone/during the cyclone/post cyclone responsibilities of a common man?

  • Steps to be taken before the cyclone:
  1. Check houses, secure loose tiles by cementing wherever necessary, repair doors and windows.
  2. Check the area around the house -remove dead or dying trees, anchor removable objects like lumber piles, loose bricks, garbage cans, sign-boards, loose zinc sheets etc.
  3. Keep some wooden boards ready so that glass windows can be boarded.
  4. Keep a hurricane Lantern filled with kerosene, flash light and enough dry cells.
  5. Promptly demolish condemned buildings.
  6. Those who have radio sets should ensure that the radio is fully serviceable in the case of transistors an extra set of batteries should be kept handy.

Steps to be taken during the cyclone:

  1. Keep your radio on and listen to latest weather warnings and advisories from the nearest All India Radio station. Pass the information to others.
  2. Avoid being misled by rumors. Pass only the. Official information you have got from the radio to others.
  3. Get away from low lying beaches or other locations which may be swept by high tides or storm waves. Leave sufficiently early before your way to high ground gets flooded. Do not delay and run the risk of being marooned.
  4. If your house is out of danger from high tides and flooding from the river, and it is well built, it is then probably the best place during weather and storm. However, please act promptly if asked to evacuate.
  • Be alert for high water in areas where streams of rivers may flood due to heavy rains.
  • Board up glass windows or put storm shutters in place. Use good wooden planks Securely fastened. Make-shift boarding may do more damage than none at all. Provide strong suitable support for outside doors.
  • If you do not have wooden boards handy paste paper strips on glasses to prevent splinters flying into the, house.
  • Get extra food, specially things which can be eaten without cooking or with very little preparation. Store extra drinking water in suitable covered vessel.
  • If you are in one of the evacuation areas, move your valuable articles to upper floors to minimise flood damage.
  • Have hurricane lantern, flash lights and/or other emergency light in working condition and keep them handy.
  • Check on everything that might blow away or be torn loose. Kerosene tins, cans, agricultural implements, garden tools, road signs and other objects become weapon of destruction in strong winds. Remove them and store them in a  covered room.
  • Be Sure that a window or door can be opened on the lee side of the house i.e. the side opposite the one facing the wind.
  • Make provisions for children and adults requiring special diets.
  • If the centre of’ ‘eye’ of the storm passes directly over your place, there will be a lull in the wind and rain, lasting for half an hour or more. During this period stay in safe place. Make emergency repairs during the lull period if necessary, but remember that strong wind will return suddenly from the opposite direction, frequently with even greater violence.
  • Be calm. Your ability to meet emergency will inspire and help others.

2. What are the causes of disaster during cyclone?

The dangers associated with cyclonic storms are generally three fold.

  • Very heavy rains causing floods
  • Strong wind
  • Storm surge

Let us discuss each separately:

  • The rainfall associated with a Cyclone vary from system to system even with the same intensity. Record rainfall in a cyclonic storm has been as low as trace to as high as 250 cms. It has been found that the intensity of rainfall is about 85 cms/day within a radius of 50 kms and about 35 cms/day between 50 to 100 kms from the centre of the storm. Precipitation of about 50 cm/day is quite common with a C.S. This phenomenal rain can cause flash flood.
    • The strong wind speed associated with a cyclonic storm. (62-88 kmph) can result into some damage to kutcha houses and tree branches likely to break off. Winds of a severe Cyclonic storm (89-117 kmph) can cause uprooting of trees, damage to pucca houses and disruption of communications. The wind associated with a very severe Cyclonic storm and super cyclonic storm can uproot big trees, cause wide spread damages to houses and installations and total disruption of communications. The maximum wind speed associated with a very severe Cyclonic storm that hit Indian coast in the past 100 years was 260 kmph in Oct, 1999 (Paradip Super cyclone).
    • The severest destructive feature of a tropical storm is the storm surge popularly called tidal waves. The coastal areas are subjected to storm surge and is accentuated if the landfall time coincides with that of high tides. This is again more if the sea bed is shallow. Storm surge as high as 15 to 20 ft. may occur when all the factors contributing to storm surge are maximum. This storm tide inundates low lying coastal areas which has far reaching consequences apart from flooding. The fertility of land is lost due to inundation by saline water for a few years to come.

3. When does a coastal station start experiencing bad weather associated with a Cyclone?

Coasts come under the influence of bad weather in the form of heavy rain, gale winds (exceeding 65 kmph) when the cyclone moves closer to the coast within 200km. Heavy rainfall generally commences about 9-12 hours before cyclone landfall. Gale force winds commence about 6-9 hours in advance of cyclone landfall. Maximum storm surge may appear at or near the landfall time.

4. What is a Storm Surge?

Storm Surge is an abnormal rise of sea level as the cyclone crosses the coast. Sea water inundates the coastal strip causing loss of life, large scale destruction to property & crop. Increased salinity in the soil over affected area makes the land unfit for agricultural use for two or three seasons.

Storm surge depends on intensity of the cyclone (Maximum winds and lowest pressure associated with it and Coastal bathymetry (shallower coastline generates surges of greater heights).

5. What is the vulnerability our coastline from the point of view of storm surge potential?

Entire Indian coast can be categorized into 4 zones

  • Very high risk zones (Surge height > 5m)
  • High risk Zone (Surge height between 3-5m)
  • Moderate risk zone (Surge height between 1.5 to 3m)
  • Minimal risk zone (Surge height < 1.5m)

Accordingly

  • The coastal areas and off-shore islands of Bengal and adjoining Bangladesh are the most storm-surge prone (~ 10-13m) – VHRZ
  • East coast of India between Paradip and Balasore in Orissa (~ 5-7m) – VHRZ
  • Andhra coast between Bapatla and Kakinada holding estuaries of two major rivers Krishna and Godavari (~ 5-7m) – VHRZ
  • Tamilnadu coast between Pamban and Nagapattinam (~ 3-5m) – HRZ
  • Gujarat along the west coast of India (~ 2-3m) –MRZ.

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