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.

Tropical Cyclones & IMD Warning

1. Tropical cyclone and its annual frequency

The tropical cyclones develop over the warm waters of the Bay of Bengal and the Arabian Sea during the months of May-June and October-November with severe intensity.

The average annual frequency of tropical cyclones in the north Indian Ocean (Bay of Bengal and Arabian Sea) is about 5. The frequency is more in the Bay of Bengal than in the Arabian Sea, the ratio being is 4:1.

The terms “hurricane” and “typhoon” are region specific names for a strong “tropical cyclone”. Tropical cyclones are called “Hurricanes” over the Atlantic Ocean and “Typhoons” over the Pacific Ocean.

A tropical cyclone (TC) is a rotational low-pressure system in tropics when the central pressure falls by 5 to 6 hPa from the surrounding and maximum sustained wind speed reaches 34 knots (about 62 kmph). It is a vast violent whirl of 150 to 800 km, spiraling around a centre and progressing along the surface of the sea at a rate of 300 to 500 km a day.

2. What is the energy potential of a Tropical Cyclone?

Tropical Cyclone can be compared to a heat engine. The energy input is from warm water and humid air over tropical oceans. Release of heat is through condensation of water vapour to water droplets/rain. Only a small percentage (3%) of this released energy is converted into Kinetic energy to maintain cyclone circulation (wind field). A mature cyclone releases energy equivalent to that of 100 hydrogen bombs.

  • Wind speed criteria for different rain bearing systems form over the ocean
SystemAssociated wind speed Knots (Kmph)
Low pressure area<17(<31)
Depression17-27 (31-49)
Deep Depression (DD)28-33 (50-61)
Cyclonic Storm (CS)34-47 (62-88)
Severe        Cyclonic       Storm (SCS)48-63 (89-117)
Very       Severe         Cyclonic Storm (VSCS)64-89 (118-166)
Extremely Severe Cyclonic Storm (ESCS)90-119 (167-221)
Super Cyclonic Storm≥ 120 (≥ 222)
Wind speed criteria for different rain bearing systems form over the ocean

3. How do the cyclones form and intensify?

In the tropics, weak pressure waves move from east to west. These are  called easterly waves. Under favourable situation, a low pressure area forms over the area of an easterly trough. This gives rise to low level convergence. If the sea is warm (sea surface temperature ≥ 26.50 C) and there is sufficient upper level divergence i.e air is blown off at higher levels from the area of low pressure, the pressure gradually falls. Low level convergence coupled with upper level divergence gives rise to vertical motion taking moist air upwards. These moistures condense at higher levels (middle troposphere) and give out latent heat of condensation. Due to release of heat of condensation the area warms up resulting into further fall in pressure. This process continues and a low pressure system gradually intensifies into a cyclonic storm.

4. What is the size of a tropical cyclone over the north Indian Ocean?

The size of a Tropical Cyclone over Indian seas varies from 50-100 km radius to 2000 km with an average of 300 –600 km.

5. What is the life period of cyclones?

Life period of a tropical cyclone over the north Indian Ocean is 5-6 days. It will have hurricane intensity for 2-4 days as against 6 days of global average.

6. What is the normal movement of a Tropical Cyclone?

Tropical cyclones move as a whole. They casually move west- northwestwards or northwestwards in the northern hemisphere. The average speed is 15-20 kmph (360-480 km per day). They may change their direction of movement towards north. During this change their speed of movement decreases to 10 kmph or even less. A larger fraction of such storms later turn towards northeast and move northeastwards very fast at a speed of 25 kmph or more.

7. How are Tropical Cyclones monitored by IMD?

IMD has a well-established and time-tested organization for monitoring and forecasting tropical cyclones. A good network of meteorological observatories (both surface and upper air) is operated by IMD, covering the entire coastline and islands. The conventional observations are supplemented by observational data from automatic weather stations (AWS), radar and satellite systems. INSAT imagery obtained at hourly intervals during cyclone situations has proved to be immensely useful in monitoring the development and movement of cyclones.

8. How track prediction is done in IMD?

IMD has one of the best forecasting system for predicting tropical cyclones, using high resolution weather prediction models including global, regional and cyclone specific models.

The ensemble forecast systems introduced in the recent past provides probabilistic guidance for track and intensity of cyclones and depressions. Regional models like Hurricane Weather Research Forecast (HWRF) have also been implemented to generate forecasts at very high resolution of 2km. IMD is also planning to make the ocean atmosphere coupled Hurricane Weather Research & Forecast model operational which has the potential to predict intensity more accurately.

9. What is our accuracy of landfall prediction?

Probability of correct forecast decreases with increasing forecast validity period. Mean forecast errors for 12, 24, 48 and 72 hours are about 49, 81,129 and 165 km respectively, which are comparable to corresponding figures of other centres like National Hurricane Centre, Miami, which monitor Atlantic Hurricanes; Typhoon Warning Centre, Tokyo, which monitors Typhoons of Northwest Pacific etc.

10. What is the organizational set up in IMD for Cyclone forecasting and Warning?

The Cyclone Warning Organization in India has a 3-tier system to cater to the needs of the maritime States. These are: Cyclone Warning Division set up at IMD Head Quarters to co-ordinate and supervise cyclone warning operations in the country and to advise the Govt. at the apex level; Area Cyclone Warning Centres at Chennai, Mumbai and Kolkata and Cyclone Warning Centres at Visakhapatnam, Ahmedabad, Bhubaneswar and Thiruvanathapuram

11. What is 4-stage warning system for Tropical Cyclones?

Expectations of Disaster Managers are longer lead time and improved accuracy of landfall forecast. But the present state of art has limitations to make the above requirements go hand in hand. Lead time depends on the formation and duration of cyclone itself which may vary considerably from one cyclone to another. However, since pre-monsoon cyclone season of 1999, IMD introduced a 4-Stage warning system to issue cyclone warnings to the disaster managers. They are as follows:

(1)    Pre-Cyclone Watch

Issued when a depression forms over the Bay of Bengal irrespective of its distance from the coast and is likely to affect Indian coast in future. The pre-cyclone watch is issued by the name of Director General of Meteorology and is issued at least 72 hours in advance of the commencement of adverse weather. It is issued at least once a day.

(2)    Cyclone Alert

Issued atleast 48 hours before the commencement of the bad weather when the cyclone is located beyond 500 Km from the coast. It is issued every three hours.

(3)    Cyclone Warning

Issued at least 24 hours before the commencement of the bad weather when the cyclone is located within 500 Km from the coast. Information about time /place of landfall are indicated in the bulletin. Confidence in estimation increases as the cyclone comes closer to the coast

(4)    Post landfall outlook

It is issued 12 hours before the cyclone landfall, when the cyclone is located within 200 Km from the coast. More accurate & specific information about time /place of landfall and associated bad weather indicated in the bulletin. In addition, the interior distraction is likely to be affected due to the cyclone are warned in this bulletin.

12.  Who are the recipients of Cyclone Warnings?

Warnings are issued for general public, fishermen, farmers and different categories of users such as central and state government officials responsible for disaster mitigation and relief, industrial and other establishments located in the coastal areas, ports, coastal shipping, railways, aviation, transport, communication and power authorities.

13.  How a common man gets information about a cyclonic storm?

Local AIR broadcast hourly (or more frequently) bulletins in local language as well as in Hindi and English. The bulletins give the location of the Cyclonic storm, its direction of movement, place and time of landfall and details of adverse weather expected over the areas likely to be affected by the storm. AIR, New Delhi issues bulletins thrice in a day giving similar information. Apart from that, the cyclone warning messages are sent to the collectors of the districts likely to be affected and the chief secretary of concerned state. The state Govt. takes necessary steps to inform the local population through their machinery such as police wireless etc. They make necessary arrangement for evacuation from coastal area and for removal of the population to other places.

14.  How does IMD keep liaison with State officials?

Area Cyclone Warning Centres (ACWCs) and Cyclone Warning Centres (CWCs) maintain liaison with the concerned state Governments in state and district levels on cyclone related activities. The cyclone warning bulletins are  communicated to the Chief Secretary, Revenue Secretary, Special Relief Commissioner, State control room, State Disaster Management Authority and concerned district collectors every three hourly. In addition, the Chief Secretary is personally briefed by Director, ACWC/CWC regularly. Before the cyclone season, ACWC/CWC organizes the precyclone preparedness meeting under the chairmanship of Chief Secretary where all the high state Govt. officials from various departments participate.

FAQ on Heat Wave

Q. What is heat wave?

Qualitatively, heat wave is a condition of air temperature which becomes fatal to human body when exposed. Quantitatively, it is defined based on the temperature thresholds over a region in terms of actual temperature or its departure from normal. In certain countries it is defined in term of the heat index based on temperature and humidity or based on extreme percentile of the temperatures. 

Q. What is criterion for declaring heat wave?

Heat wave is considered if maximum temperature of a station reaches at least 400C or more for Plains and at least 300C or more for Hilly regions.

  1. Based on Departure from Normal

Heat Wave:                           Departure from normal is   4.50C to 6.40C

Severe Heat Wave:               Departure from normal is >6.40C             

  • Based on Actual Maximum Temperature

Heat Wave:                   When actual maximum temperature ≥ 450C

Severe Heat Wave:    When actual maximum temperature ≥470C

If above criteria met at least in 2 stations in a Meteorological sub-division for at least two consecutive days and it declared on the second day.

Q. What is a criterion for describing Heat Wave for coastal stations?

When maximum temperature departure is 4.50C or more from normal, Heat Wave may be described provided actual maximum temperature is 370C or more.

Q. What is warm night?

It is considered only when maximum temperature remains 400C or more. It is defined based on departures or actual minimum temperatures as follows:

Warm night:                 minimum temperature departure is   4.50C to 6.40C

Very warm night:         minimum temperature departure is >6.40C

Q. What is the period of heat wave over India?

It is occurring mainly during March to June and in some rare cases even in July. The peak month of the heat wave over India is May.

Q. What are the heat wave prone states over India?

Heat wave generally occurs over plains of northwest India, Central, East & north Peninsular India during March to June. It covers Punjab, Haryana, Delhi, Uttar Pradesh, Bihar, Jharkhand, West Bengal, Odisha, Madhya Pradesh, Rajasthan, Gujarat, parts of Maharashtra & Karnataka, Andhra Pradesh and Telengana. Sometimes it occurs over Tamilnadu & Kerala also. Heat waves adversely affect human and animal lives. However, maximum temperatures more than 45°C observed mainly over Rajasthan and Vidarbha region in month of May.

Q. How India Meteorological Department (IMD) monitors the Heat wave?

IMD has a big network of surface observatories covering entire country to measure various metrological parameters like Temperature, Relative humidity, pressure, wind speed & direction etc. Based on daily maximum temperature station data, climatology of maximum temperature is prepared for the period 1981-2010 to find out normal maximum temperature of the day for particular station. Thereafter, IMD declared heat wave over the region as per its definition.     

Q. What is the temporal range of temperature forecast issued by IMD?

IMD issues temperature forecast & warning in following range:

  1. Short to medium range  (lead time/validity of 1 to 5 days)
  2. Extended range  (lead time/validity upto 4 weeks)
  3. Seasonal range  (lead time/validity upto 3 months)

Q. What is the spatial range of temperature forecast issued by IMD?

IMD issues location, District, Meteorological Sub-division and Homogeneous regions temperature forecast to its various users and keep in IMD Website (https://mausam.imd.gov.in/).

Q. How IMD predicts the Heat wave?

IMD predicts heat wave based on synoptic analysis of various meteorological parameters and from the consensus guidance from various regional & global numerical prediction models like, WRF, GFS, GEFS, NCUM, UMEPS, UM Regional etc. run in Ministry of Earth Sciences (MoES) and other international models available under bilateral multi-institutional arrangement   

Q. How common man may get IMD Heat wave information?

A common man may get heat wave information from, All India Weather Forecast Bulletin (https://mausam.imd.gov.in/imd_latest/contents/all_india_forcast_bulletin.php) and special heat wave guidance bulletins (http://internal.imd.gov.in/pages/heatwave_mausam.php) during 1 April to 30 June everyday. The heat wave information is shared with concerned State Government Authority, Media and other stakeholders like Indian Railway, Health departments, Power Sector etc. The general public is informed through Print & Electronics Media.  

Q. How frequently Heat wave bulletins are issued?

5 days Heat wave warnings are updated four times in day (based on 0530, 0830, 1430 & 1730 hours IST) in All India Weather Forecast Bulletin (https://mausam.imd.gov.in/imd_latest/contents/all_india_forcast_bulletin.php) by National Weather Forecasting Centre (NWFC), IMD, New Delhi. In the Morning and Evening (at 0800 & 1600 hours IST) special heat wave guidance bulletins (http://internal.imd.gov.in/pages/heatwave_mausam.php) are also issued by NWFC. The district wise heat wave warnings are issued by State level Meteorological Centre/Regional Meteorological Centres of IMD.

Q. How does IMD co-ordinate with central & state disaster managers for Heat wave?

IMD issues special heat wave warning guidance bulletins (at 0800 & 1600 hours IST) at meteorological sub-division & district levels to different users like, Ministry of Home Affairs, National Disaster Management Authority, State Disaster Management Authority,  Deputy Commissioner/District Magistrates of different districts of states, health department, Indian Railway, Road transport, Media etc.  IMD conducts the preseason exercise at state & national level. IMD also contributes in the preparation of heat wave guidelines and heat action plan. IMD provides the required past data for heat wave advisories and development.  

.

Q. What are favorable conditions for Heat wave?

  1. Transportation / Prevalence of hot dry air over a region (There should be a region of warm dry air and appropriate flow pattern for transporting hot air over the region).
  2. Absence of moisture in the upper atmosphere (As the presence of moisture restricts the temperature rise).
  3. The sky should be practically cloudless (To allow maximum insulation over the region).
  4. Large amplitude anti-cyclonic flow over the area.

Heat waves generally develop over Northwest India and spread gradually eastwards & southwards but not westwards (since the prevailing winds during the season are westerly to northwesterly). But on some occasions, heat wave may also develop over any region in situ under the favorable conditions.

Q. How heat discomfort is determined?

It is determined by a combination of meteorological (temperature, Relative Humidity, wind, direct sunshine), social/cultural (clothing, occupation, accommodation) and physiological (health, fitness, age, level of acclimatization) factors.

(source: https://www.ndma.gov.in/images/guidelines/heatwaveguidelines2017.pdf)

Q. What is heat index?

The heat index is the combination of air temperature and relative humidity, it measure of how hot it really feels when relative humidity is factored in with the actual air temperature.

Q. What is impact based heat wave warning issue by India Meteorological Department (IMD)?

India Meteorological Department issues following colour code impact based heat warning jointly with National Disaster Management Authority.  

NilAlertWarningImpactSuggested Actions
Green (No action)Normal DayMaximum temperatures are near normalMaximum temperatures are near normalNil
Yellow Alert (Be updated)Heat AlertHeat wave conditions at isolated pockets  persists on 2 daysModerate temperature. Heat is tolerable for general public but moderate health concern for vulnerable people e.g. infants, elderly, people with chronic diseasesModerate temperature. Heat is tolerable for general public but moderate health concern for vulnerable people e.g. infants, elderly, people with chronic diseases
Severe Heat Alert for the daySevere Heat Alert for the day(i) Severe heat wave conditions persists for 2 days (ii) Through not severe, but  heat wave  persists for 4 days or more(i) Severe heat wave conditions persists for 2 days (ii) Through not severe, but  heat wave  persists for 4 days or more(b) Avoid heat exposure– keep cool. Avoid dehydration. (b) Drink sufficient water- even if not thirsty. (c) Use ORS, homemade drinks like lassi, torani (rice water), lemon water, buttermilk, etc. to keep yourself hydrated
Red Alert (Take Action)Extreme Heat Alert for the day(i) Severe heat wave persists for more than 2 days. (ii) Total number of heat/severe heat wave days exceeding 6 days.Severe Heat Alert for the dayExtreme care needed for vulnerable people.

Q. Health Impacts of Heat Waves?

The health impacts of Heat Waves typically involve dehydration, heat cramps, heat exhaustion and/or heat stroke. The signs and symptoms are as follows:

  • Heat Cramps: Ederna (swelling) and Syncope (Fainting) generally accompanied by fever below 39*C i.e.102*F.
  • Heat Exhaustion: Fatigue, weakness, dizziness, headache, nausea, vomiting, muscle cramps and sweating.
  • Heat Stoke: Body temperatures of 40*C i.e. 104*F or more along with delirium, seizures or coma. This is a potential fatal condition

(source: https://ndma.gov.in/en/2013-05-03-08-06-02/disaster/natural-disaster/heat-wave.html)

Q. What are the measures one should take to minimise the impact during the heat wave?

  • Avoid going out in the sun, especially between 12.00 noon and 3.00 p.m.
  • Drink sufficient water and as often as possible, even if not thirsty
  • Wear lightweight, light-coloured, loose, and porous cotton clothes. Use protective goggles, umbrella/hat, shoes or chappals while going out in sun.
  • Avoid strenuous activities when the outside temperature is high. Avoid working outside between 12 noon and 3 p.m.
  • While travelling, carry water with you.
  • Avoid alcohol, tea, coffee and carbonated soft drinks, which dehydrates the body.
  • Avoid high-protein food and do not eat stale food.
  • If you work outside, use a hat or an umbrella and also use a damp cloth on your head, neck, face and limbs
  • Do not leave children or pets in parked vehicles
  • If you feel faint or ill, see a doctor immediately.
  • Use ORS, homemade drinks like lassi, torani (rice water), lemon water, buttermilk, etc. which helps to re-hydrate the body.
  • Keep animals in shade and give them plenty of water to drink.
  • Keep your home cool, use curtains, shutters or sunshade and open windows at night.
  • Use fans, damp clothing and take bath in cold water frequently.

(source: https://ndma.gov.in/en/heat-do-s-and-dont-s.html)

Q. What you should do, if you think someone is suffering from the heat?

  • Move the person to a cool place under the shade
  • Give water or a rehydrating drink (if the person is still conscious)
  • Fan the person
  • Consult a doctor if symptoms get worse or are long lasting or the person is unconscious
  • Do not give alcohol, caffeine or aerated drink
  • Cool the person by putting a cool wet cloth on his/her face/body
  • Loosen clothes for better ventilation

(source: https://ndma.gov.in/en/heat-recover-and-build.html)

Q. What are symptoms of Sunburn and its first aid?

Symptoms: Skin redness and pain, possible swelling, blisters, fever and headaches.

First Aid: Take a shower, using soap, to remove oils that may block pores preventing the body from cooling naturally. If blisters occur, apply dry, sterile dressings and get medical attention.

(source: https://ndma.gov.in/images/guidelines/guidelines-heat-wave.pdf)

Q. What are symptoms of Heat Cramps and its first aid?

Symptoms: Painful spasms usually in leg and abdominal muscles or extremities. Heavy sweating.

First Aid: Move to cool or shaded place. Apply firm pressure on cramping muscles or gentle massage to relieve spasm. Give sips of water. If nausea occurs, discontinue.

(source: https://ndma.gov.in/images/guidelines/guidelines-heat-wave.pdf)

Q. What are symptoms of Heat Exhaustion and its first aid?

Symptoms: Heavy sweating, weakness, skin cold, pale, headache and clammy. Weak pulse. Normal temperature possible. Fainting, vomiting.

First Aid: Get victim to lie down in a cool place. Loosen clothing. Apply cool, wet cloth. Fan or move victim to air-conditioned place. Give sips of water slowly and If nausea occurs, discontinue. If vomiting occurs, seek immediate medical attention. Or call 108 and 102 for Ambulance.

(source: https://ndma.gov.in/images/guidelines/guidelines-heat-wave.pdf)

Q. What are symptoms of Heat Stroke (Sun Stroke) and its first aid?

Symptoms: High body temperature (106+F). Hot, dry skin. Rapid, strong pulse. Possible unconsciousness. Victim will likely not sweat.

First Aid: Heat stroke is a severe medical emergency. Call 108 and 102 for Ambulance for emergency medical services or take the victim to a hospital immediately. Delay can be fatal. Move victim to a cooler environment. Try a cool bath or sponging to reduce body temperature. Use extreme caution. Remove clothing. Use fans and/or air conditioners. DO NOT GIVE FLUIDS.

 (source: https://ndma.gov.in/images/guidelines/guidelines-heat-wave.pdf)

Q. What are the measures one should do to minimize the impact during heat wave?

  • Listen to Radio, watch TV, read News paper for local weather forecast to know if a heat wave is on the way
    • Drink sufficient water and as often as possible, even if not thirsty
  • Wear lightweight, light-coloured, loose, and porous cotton clothes. Use protective goggles, umbrella/hat, shoes or chappals while going out in sun.
    • While travelling, carry water with you.
  • If you work outside, use a hat or an umbrella and also use a damp cloth on your head, neck, face and limbs.
  • Use ORS, homemade drinks like lassi, torani (rice water), lemon water, buttermilk, etc. which help to re-hydrate the body.
  • Recognize the signs of heat stroke, heat rash or heat cramps such as weakness, dizziness, headache, nausea, sweating and seizures. If you feel faint or ill, see a doctor immediately.
    • Keep animals in shade and give them plenty of water to drink.
    • Keep your home cool, use curtains, shutters or sunshade and open windows at night.
    • Use fans, damp clothing and take bath in cold water frequently.
    • Provide cool drinking water near work place.
    • Caution workers to avoid direct sunlight.
    • Schedule strenuous jobs to cooler times of the day.
    • Increasing the frequency and length of rest breaks for outdoor activities.
    • Pregnant workers and workers with a medical condition should be given additional attention.

(source: https://ndma.gov.in/images/guidelines/guidelines-heat-wave.pdf)

Q. What one should not do to minimize the impact during heat wave?

  • Listen Do not leave children or pets in parked vehicles.
  • Avoid going out in the sun, especially between 12.00 noon and 3.00 p.m.
  • Avoid wearing dark, heavy or tight clothing.
  • Avoid strenuous activities when the outside temperature is high. Avoid working outside between 12 noon and 3 p.m.
  • Avoid cooking during peak hours. Open doors and windows to ventilate cooking area adequately.
  • Avoid alcohol, tea, coffee and carbonated soft drinks, which dehydrates the body.
  • Avoid high-protein food and do not eat stale food..

(source: https://ndma.gov.in/images/guidelines/guidelines-heat-wave.pdf)

Q. What is the accuracy of heat wave warning?

Heat wave skill (Probability of Detection (PoD) and Missing Rate (MR)) during 2014 to 2019 is as follow:

There is significant improvement in Day 1 (D1) to Day 5 (D5) forecast warning in the recent years specifically for Day 3 (D3) to Day 5 (D5) warning. The accuracy of warning in term of PoD is more than 80% for D1 & D2. 

Q. Who can be contacted for heat wave information & warning in IMD?

Round the clock duty officer is available in National Weather Forecasting Centre, IMD,

New Delhi. The contact address is given below:

National Weather Forecasting Centre,

India Metrological Department,

Lodi Road, New Delhi

Phone: 011-24631913, 42964160

Meteorological Centre Ranchi, Jharkhand

Meteorological Centre Ranchi was established on 27 May 2002 after formation of the state Jharkhand
on 15 November 2000. It is the National Meteorological Service of the state and the principal
government agency in all matters relating to meteorology to provide weather forecast services to all
users like general public of Jharkhand and concerned Government agencies.


Major responsibilities of Meteorological Centre Ranchi are:
 To take meteorological observations and to provide current and forecast of meteorological
information for weather-sensitive activities like agriculture, irrigation, aviation, road transport,
etc.
 To warn against severe weather phenomena like thunderstorms, lightning, squall, heavy rains,
cold and heat waves, etc., which cause destruction of life and property.
 To provide meteorological statistics required for agriculture, water resource management,
disaster management to state Governments and non-Government agencies and general public for
assessment of damages and insurances.
 Archival of data.
 Research and development.


Jharkhand is a state in the eastern part of India. The main seasons are summer, rainy and winter. The summer is characterized by mean maximum temperature around 35°C. The southwest monsoon brings nearly all the state’s annual rainfall which is about 1054.7 mm. Nearly half of the annual precipitation falls in July and August. The winter season is characterized by mean minimum temperature around 11°C. Agriculture is important sector in the economy of Jharkhand. Farmers produce several crops such as rice, wheat, maize, pulses, potatoes, and vegetables such as tomato, carrots, cabbage, brinjal, pumpkin, and papaya.
Observational Network in Jharkhand:
 Surface observatory: 3 (Ranchi, Daltonganj, Jamshedpur)
 Part time Surface observatory: 2 (Chaibasa, Bokaro)
 Rain gauge stations: 81(at least one in each district)
 Upper air observatory: 1 (GPS based RSRW)
 Automatic weather stations (AWS): 13
 Agro AWS: 3
 Automatic rain gauge (ARG) stations: 28
 Athalometer (black carbon monitoring equipment): 1
 Radiation monitoring equipment: 1
 Sunshine recorder: 1


Meteorological services provided by M. C. Ranchi:
 Daily weather forecast and severe weather warning for five days with two days outlook.
 Nowcast for thunderstorm and lightning for 3 hours.
 Extended range forecast services for two weeks.
 Round the clock aviation meteorological services at B.M.Airport Ranchi and Sonari Airport, Jamshedpur.
 Agro Advisory Services for all 263 blocks of Jharkhand for five days.


Meteorological Services for Civil Aviation: M. C. Ranchi provides round the clock service to the civil aviation sector as per requirements prescribed by the ICAO and the DGCA. The web based information dissemination system known as On-line Briefing System (OLBS) of IMD is being used to generate meteorological briefing for pilots. The briefing and documentation to the operators is provided through automated means and email.


Agro meteorological advisory services:
 Agro Advisory Services (AAS) provided for farmers in collaboration with Birsa Agriculture University Ranchi and Agriculture Department, Government of Jharkhand.
 Block wise quantitative value added forecast up to five days is issued to the Agro-meteorological field units (AMFUs) (Ranchi, Darisai and Dumka), Krishi Vigyan Kendra (KVK), and Gramin Krishi Mausam Seva (GKMS) Kendra.

Major achievements:
 Agro meteorological advisory services are augmented from district level to block level (24 districts to 263 blocks) from 1 June 2019. An Excel based program is developed to make it user friendly for real time use.
 A location specific SMS based Nowcast and dissemination system is developed and
implemented for thunderstorm and lightning warning over Jharkhand from 1 March 2020 by joint collaboration of Meteorological Centre Ranchi, Jharkhand space application Centre(Govt. of Jharkhand), and state disaster management authority of Jharkhand.
 Implementation of Extended range forecast services for two weeks.


Dissemination of weather forecast and warning:
Weather forecasts and warnings are disseminated to general public of Jharkhand, state Government officials, Disaster management authorities, Media, Railways, Road transport department, Power sector, Water resource management authorities, Civil work department, Defence authorities, Public work department, GKMS, KVKs, AMFUs, Academic institutes, Agriculture departments and Universities through website, email, WhatsApp, SMS, Facebook, Twitter, Telephone.


Future plan for augmentation of Observational network:
 Installation of AWS at Tourism places.
 Installation of AWS at Krishi Vigyan Kendra, and Gramin Krishi Mausam Seva Kendra.
 Installation of AWS at Kendriya Vidyalaya.
 Installation of Doppler weather radar at Ranchi.

Analysis of Appreciably above normal maximum temperatures across west and southern parts of India during 13-19 February, 2020

  1.  Introduction

 In this report an attempt is made to analyze the above normal temperatures across west and southern parts of India during 13-19 February, 2020. Middle February is a transition period from winter to summer in southern parts of India. During this period temperatures rises gradually over southern parts of the country. This pattern varies from year to year. This year appreciably above normal maximum temperatures reported over west and southern parts of the country during 13-19 February. Media also reported the same. On 17th February, Santacruz (Mumbai) reported highest maximum temperature in the country that was 38.1°C. 

2.  Observed temperature over West and southern parts of India 13-19 February

Refer table 1 and 2

Table 1:    Report on above normal temperatures over South and West India During 13 to 19 February 2020.

          DateMaximum Temperature Departures (Places)Highest Maximum Temperature in °C
Markedly above normal (5.1°C or more)Appreciably above normal (3.1°C to 5.0°C)Above normal (1.6°C to 3.0°C)
13-02-2020   Many places- Konkan & Goa. Few places- Saurashtra & Kutch.  Most places- Coastal Karnataka. Many places- Gujarat Region, Vidarbha, Kerala & Mahe, Lakshadweep. Isolated places- North Interior Karnataka and Tamilnadu, Puducherry & Karikal.38.4Gulbarga (North Interior Karnataka).  
14-02-2020 Most places- Konkan & Goa. Few places- Saurashtra & Kutch and Coastal Andhra Pradesh & Yanam.Most places- Lakshadweep. Many places- Vidarbha, Odisha, Coastal Karnataka and Tamil Nadu, Puducherry & Karaikal. Few places- Gujarat Region Isolated places- Telangana, South Interior Karnataka.37.7-Vengurla (Konkan & Goa).  
15-02-2020 Isolated places-  Saurashtra & KutchMost places- Coastal Karnataka. Many places- Konkan & Goa, South Interior Karnataka, Kerala & Mahe and Tamil Nadu, Puducherry & Karaikal. Few places- Gujarat Region Isolated places- Madhya Maharashtra, Vidarbha, Coastal Andhra Pradesh & Yanam and Lakshadweep.  37.1-Palakkad (Kerala & Mahe).
16.02.2020 Many places– Saurashtra & Kutch.Most places- East Rajasthan and Gujarat region. Many places- Konkan & Goa, Coastal & North Interior Karnataka and Lakshadweep. Few places- South Interior Karnataka. Isolated places- Telangana, Coastal Andhra Pradesh & Yanam.36.6- Gulbarga (North Interior Karnataka).
17.02.2020Few places- Saurashtra & Kutch and Konkan & Goa.Many places– Gujarat region; Few places– Kerala & Mahe.Few places– Vidarbha, Madhya Maharashtra and Coastal Karnataka. Isolated places– Interior Karnataka and Coastal Andhra Pradesh. 38.1- Santacruz (Mumbai).                               
18.02.2020Many places-Saurashtra & Kutch and Konkan & Goa.Most places- Gujarat Region. Isolated places– Madhya Maharashtra, Vidarbha, Kerala & Mahe.Few places-Coastal & South Interior Karnataka and Tamil Nadu, Puducherry & Karaikal. Isolated places– Lakshadweep.  37.5- Vengurla (Konkan & Goa).
19.02.2020Few places- Saurashtra & Kutch.Many places- Gujarat Region and Konkan & Goa. Isolated places– Vidarbha, Madhya Maharashtra.Many places– Marathawada and Kerala & Mahe. Few places- Coastal Karnataka and Tamil Nadu, Puducherry & Karaikal. Isolated places-North Interior Karnataka.36.6 – Amreli (Saurashtra & Kutch) and Gulbarga (North Interior Karnataka).

Table 2: Stations exceeding 35 °C Maximum Temperature

DateSub-divisionsMaximum Temperature (Stations) in °C
14.02.2020Konkan & Goa Coastal Karnataka North Interior Karnataka Kerala TamilnaduMumbai- 35.1, Ratnagiri-36.6 & Vengurla- 37.7, Karwar -36.5, Gulbarga-35.4, Cannur-35.2, Pallakad-36.4, Thrissur-36.3, Cochin-35.4, Kottyam-36.4, Punalur-37.5, Selem-35.1, K. Paramarthy-35.5, Madurai-35.4
15.02.2020Madhya Maharashtra,  Marathbada Coastal Karnataka, North Interior Karnataka,  Kerala,  TamilnaduAhmednagar-35.4, Solapur-35.2, Karwar-35.4, Gulbarga-36.9,  Cannur-35.4, Pallakad-37.1, Thrissur-36.5, Kottyam-35.5, Punalur-35.5, Selem-36.2, K. Paramarthy-35.8, Madurai-35.6, Tiruchchirapalli-35.2
16.02.2020Saurashtra & Kutch,  Gujarat, Madhya Maharashtra, Coastal Karnataka, North Interior Karnataka, KeralaBhuj-35.1, Surat-35.9, Sanghi-35.2, Shirli-35.1, Manglore-35.7, Gulbarga-36.6, Cannur-36.2, Thrissur-36.5, Kottyam-35.7, Punalur-36.6, Kozhocode-36.0
17.02.2020Saurashtra & Kutch, Gujarat, Madhya Maharashtra, Vidharbha,   Konkan & Goa Coastal Karnataka, North Interior Karnataka, KeralaBhuj-35.8, Nalia-35.4, Kandla-35.2, Rajkot-35.8, Porbandar-36.2, Amerli-36.2, Mahua-35.4, Surat-36.4, Dessa-35.9, Sanghi-35.3, Solapur-36.0, Ahmednagar-35.0, Akola-35.2, Mumbai/Santacuuz-38.1, Ratnagiri-36.8, Vengurla-36.4, Goa-36.5, Karwar-35.3, Manglore-36.8, Gulbarga-36.7 Cannur-37.2, Thrissur-35.7, Kottyam-37.8, Punnalur-36.6, Cochin-36.7
18.02.2020Saurashtra & Kutch, Gujarat Madhya Maharashtra, Vidarbha, Konkan & Goa, Coastal Karnataka, North Interior Karnataka, Kerala.Bhuj-36.8, Nalia-36.0, Kandla-35.4, Rajkot-36.8, Porbandar-36.0, Amerli-36.8, Mahua-36.0, Dwarka-35.3, Sundernagar-35.8, Keshod-36.6),Surat-36.9, Baroda-36.1, Ahmedabad-35.3, Sanghi-35.4, Solapur-35.6, Akola-35.9 Ahmednagar-36.2, Jeur-35.2, Mumbai/Santacuuz-36.5, Ratnagiri-37.0, Vengurla-37.5, Goa-36.3, Kolaba-35.6, Karwar-36.2, Manglore-35.2, Gulbarga-36.2, Cannur-37.2, Thrissur-35.3, Kottyam-35.5, Punnalur-35.5, Cochin-36.0), Tamilnadu (Madurai-36.8
19.02.2020Saurashtra & Kutch, Gujarat, Madhya Maharashtra, Vidarbha, Konkan & Goa, Marathbada, Coastal Karnataka, North Interior Karnataka, Kerala, TamilnaduRajkot-35.3, Amreli-36.6, Sundernagar-35.7, Baroda-35.0,  Jalgaon-35.4, Malegaon-36.0, Sanghi-35.5, Jeur-35.0, Akola-36.2, Brahemapuri-36.0, Mumbai/Santacuuz-34.8, Parbhani-35.1, Solapur-36.4, Ratnagiri-35.1,  Manglore-35.1, Gulbarga-36.6, Cannur-35.4, Thrissur-35.7, Kottyam-35.2, Cochin-36.1, Madurai-36.4

From the above it is observed that about 5 stations in Kerala are reporting maximum temperatures above 35°C daily. It is also observed that   on 17.02.2020 & 18.02.2020 the number of stations more than 35°C increased in Saurashtra & Kutch, Gujarat, Konkan & Goa and Mumbai recorded the highest temperature in that day. Then on 19.02.2020 temperature reduced slightly and the number of stations with maximum temperature more than 35°C reduced. Madurai in Tamilnadu also reporting maximum temperature above 35°C.

3. Associated synoptic features and wind analysis

Figure 1 shows IMD: GFS Model (12 Km) 925 hPa Wind (kt) for 00 UTC of 13th to 19th February, 2020.  

Figure 1(a) shows that on 13th February, strong north-westerly winds were prevailing over north-west India, however south-westerly, easterly winds over south India on that day. Figure 1(b) & (c) show that on 14th & 15th February, strong north-westerly winds were prevailing over north India, however southerly, south-easterly winds were prevailing over west and south India on that day. Figure 1(d) shows that on 16th February, southerly, south-easterly winds were prevailing over west and south India on that day. Figure 1(e) shows that on 17th February, easterly, south-easterly & South-westerly winds were prevailing over west and south India on that day. Figure 1(f) shows that on 18th February, south-easterly & South-westerly winds were prevailing over west and south India on that day. Figure 1(g) shows that on 19th February, southerly & South-easterly winds were prevailing over west and south India on that day.

Table 3: Feb 2020 – List of Western Disturbances (WD)

1. Western Disturbance (30th January, 2020 -02nd February, 2020)
2.  Western Disturbance (02nd February, 2020 -06nd February, 2020)
3. Western Disturbance (05th February, 2020 -08th February, 2020)
4. Western Disturbance (10th February, 2020 – 13th February, 2020)
5. Western Disturbance (11th February, 2020 – 15th February, 2020)
6. Western Disturbance (15th February, 2020 – 17th February, 2020)

7. Western Disturbance (17th February, 2020 –     19th February, 2020)  

Table 3 shows the list of WD affected northern India during 1st fortnight of Feb 2020. It shows total 7 WDs (average is 2 WD) have affected.

Northwesterly winds could not penetrate up to North Tamil Nadu and North Karnataka and Kerala. These winds remained absent as successive Western Disturbances kept inducing cyclonic circulations over Rajasthan and central parts of the country, leading to the occasional formation of confluence that blocked cold northerly winds from reaching southern states. Interaction between easterly and westerly could get rain over eastern India but not over south and west India. Frequent WDs impacted North, Central, east and northeast India.

From the synops of different stations it is found that most of the time week winds up to 5 knots prevailed with no northerly components. Westerly, easterly or south-westerly winds prevailed and this helped for higher temperature over these areas.

Possible reasons for above normal temperature in South India including west coast and Saurashtra & Kutch and Gujarat may be;

1.During past six to seven days no major rainfall activity reported over these areas. Almost weather remained dry over these areas.

2. Transition phase from winter to summer.  Although February is a transition period for southern states from winter season, during this entire winter season, cold wave from the north had not reached the region.

  • Summary

In this report an attempt is made to find out the possible reasons of appreciably above normal maximum temperatures across west and southern part of India during 13-19 February, 2020. Details of the observed maximum temperatures are listed in this report.

During the month of February, 2020 Seven WDs observed and all of them affected North, Central and East and North-East India with good rainfall activities. But such frequent mid latitude WDs resulted westerly pattern to be dominate mode.  Resulting into, no major rainfall activities over the West and South India and mainly dry weather prevailed in most January and February including the period of 13th February to 19th February for these areas. Also, during 13th February to 19th February, no northerly winds prevailed over the region resulting into above normal maximum temperatures during 13th February to 19th February. 

Report Compiled by:

Shashi Kant, Surendra Pratap Singh, R. K. Jenamani

Heat Wave conditions over India

During hot weather period (March to July) surface temperatures over many parts of India abnormally shoot up, particularly over North and central India. Annual cycle of All-India daily maximum and minimum temperatures is as given in the below figure.

Figure 1: Annual cycle of All-India daily maximum and minimum temperatures.

As per the above figure, maximum temperatures are highest in pre-monsoon days and started decreasing in monsoon days.

As per India Meteorological Department’s criteria, Heat Wave conditions are defined as:

 Heat Wave:

It should be based on the actual maximum temperature of a station. Heat Wave is considered when maximum temperature of a station is 400C or more for plains and 30°C or less for Hilly regions. 

Based on Departure

Heat Wave:  Positive Departure from normal is 4.5°C to 6.4°C

Severe Heat Wave:  Positive Departure from normal is more than 6.4°C

Based on Actual Minimum Temperature    (For plain stations only)

Heat Wave:                                 When maximum temperature is ³45°C

Severe Heat Wave:                     When minimum temperature is ³47°C

Heat Wave conditions for coastal stations

When minimum temperature departure is +4.5°C or more over a station, “Heat Wave” may be described if the maximum temperature is 370C or more.

To declare heat wave, the following criteria should be met at least in 2 stations in a Meteorological sub-division for at least two consecutive days and it will be declared on the second day.  Forecasts of heat wave over a sub-division will be issued only if at least two stations in the sub-division are expected to experience such conditions.

  • Heat wave occurs mostly over an interior plain area when dry and warmer air is transported in a region with clear skies and hence maximum isolation during the summer season.
  • Bay islands, Lakshadweep, Tamil Nadu, Kerala, Coastal and South Interior Karnataka are not affected by heat waves due to the occurrence of maritime air over these regions.
  • Heat waves generally develop over Northwest India and spread gradually eastwards & southwards but not westwards (since the prevailing winds during the season are westerly to northwesterly). But on some occasions, heat wave may also develop over any region in situ under the favorable conditions.

Heat wave impacts rural and urban areas, natural habitats like forests, water resources, poultry and a range of sectors like agriculture, health, power etc, Though there is no universally acceptable or uniform definition for a heatwave, they are understood to be periods of abnormally high temperatures, more than the normal maximum temperature that occurs during the pre-monsoon (April to June) summer season. In India heat -waves typically occur between March to June, and in some rare cases even extend till July. Heat waves are more frequent over the Indo-Gangetic plains of India.

Health Impacts of Heat Waves

The health impacts of Heat Waves typically involve dehydration, heat cramps, heat exhaustion and/or heat stroke. The signs and symptoms are as follows:

  • Heat Cramps: Ederna (swelling) and Syncope (fainting) generally accompanied by fever below 39°C i.e.102°F.
  • Heat Exhaustion: fatigue, weakness, dizziness, headache, nausea, vomiting, muscle cramps and sweating.
  • Heat Stroke: body temperatures of 40°C i.e. 104°F or more along with delirium, seizures or coma. This is a potentially fatal condition.

What causes a heat wave?

  • A heat wave is formed when static high pressure generated in the upper atmosphere over a region for several days. This static high pressure generates a hot mass of air, which is stagnant for many days, which resulted the trapping of more heat that also reduce the convection currents. The high pressure acts as a barrier and forces the mass of air to sink to the surface of the land that prevents heat to rise.
  • This hot mass of air accumulates only heat and humidity without any trace of precipitation that causes abnormally high temperatures. It is very often during the summer season, from March to July in the Indian Region.
  • Seasonal climatology map of number of HW days and SHW days over India during the hot weather season (March – July) for the period 1961-2010 is as in Figure 2.
Figure 2: Seasonal climatology map of number of HW days and SHW days over India during the hot weather season (March – July) for the period 1961-2010.

Monitoring and forecasting process:

IMD utilizes all its resources to monitor heat wave round the clock. It issues forecast& warning with a lead period of 05 days against the heat wave to the general public, disaster managers, media and other stake holders using following Impact Based Forecast table as per requirement of Disaster Management.

Figure 3: Impact Based Warning Forecast table followed by India Meteorological Department.

Compiled By: Surendra Pratap Singh, Naresh Kumar.

Cold Wave & Cold Day conditions over North India

Introduction:

The plains of North India experience Cold Wave and Cold Day conditions during winter season (December-February) every year. It is a severe weather phenomenon which causes loss to life and public property. As per India Meteorological Department’s criteria, Cold Wave and Cold Day conditions are defined as:

(A)   Cold Wave:

It should be based on the actual minimum temperature of a station. Cold Wave is considered when minimum temperature of a station is 100C or less for plains and 0°C or less for Hilly regions. 

Based on Departure

        i)          Cold Wave:                           Negative Departure from normal is 4.5°C to 6.4°C

       ii)         Severe Cold Wave:                Negative Departure from normal is more than 6.4°C

Based on Actual Minimum Temperature    (For plain stations only)

  1. Cold Wave:                                 When minimum temperature is ≤ 04°C
  2. Severe Cold Wave:                     When minimum temperature is ≤ 02°C

Cold Wave conditions for coastal stations

When minimum temperature departure is -4.5°C or less over a station, “Cold Wave” may be described if the minimum temperature is 150C or less.

(B)   Cold Day:

It should be considered when minimum temperature is 100C or less for plains and 0°C or less for Hilly regions.

Cold day:                   Maximum Temperature Departure is -4.5°C to -6.4°C

Severe Cold day:       Maximum Temperature Departure is < -6.4°C   

Factors causing Cold Wave Conditions:

  • Cold Wave conditions are associated with fall in minimum temperatures during the Winter season. In this season prevailing winds over the Indo Gangetic Plains (IGP) are northwesterlies. As northwesterlies are the winds from colder regions of Central Asia/Hindukush region, they bring temperature fall over the IGP and hence the Cold Wave Conditions.
  • Whenever a Western Disturbance (WD) approaches clouding develops over IGP bringing fall in Maximum temperatures and rise in minimum temperatures. Thus, Cold Wave conditions over IGP get abated at the approach of a WD.
  • When a WD moves away from the Indian region, clear skies start appearing over the IGP leading to rise in maximum and fall in minimum temperatures.
  • Whenever a WD affects North India, winds in lower levels over the region are either from Arabian Sea or from both Bay of Bengal and Arabian Sea. Given that both types of winds are the moist ones, minimum temperatures rise. At the same time, clouding over the region leads to lesser penetration of solar insolation into the earth and hence fall in maximum temperatures.
  • Formation of an anticyclone in lower and mid tropospheric levels is also a driver of Cold Waves. Such an anti-cyclone gives rise to sinking motion over the IGP leading to fall in minimum temperatures.

Factors causing Cold Day Conditions:

  • Cold Day conditions are associated with fall in maximum temperatures during the Winter season. Cold Day conditions occur when there is persistent low clouding over North Indian plains/IGP in the winter season.
  •  Low clouds prevent solar insolation entering into earth’s surface which causes fall in maximum temperatures.
  • Left entrance and right exit of a Jet core belong to upper level convergence which in turn causes sinking motion over the surface hence causing Cold Wave and Cold Day conditions.
  • If an active WD affects North India in the winter season and causes widespread rain over the region along with isolated hailstorms it leaves behind abundant moisture over the IGP. Now if after the passage of the WD, lower level westerlies (cold and dry) are not strong enough to absorb this abundant moisture it will cause persistent low cloud cover and hence the Severe Cold Day conditions over the region. Similar phenomenon was witnessed during second half of December, 2019. (Figure below)
  • Development of anomalous high over the region causes low cloud cover which in turn leads to preventing the solar heating of the earth surface and hence the severe cold day conditions. (Figure below)
Figure: Ridge and trough lines being shown in 925 hPa mean geopotential height chart for 16-31 December, 2019.

Monitoring and forecasting process:

IMD utilizes all its resources to monitor round the clock forecast with a lead period of 05 days and warn against the adverse weather to the general public, disaster managers, media and other stake holders. For monitoring the weather systems, IMD uses all type of Synoptic charts, INSAT-3D Rapid half hourly imagery, every 10 minutes DWR products for Srinagar, Patiala, Delhi, Lucknow, Jaipur and Bhopal. Various Numerical Prediction Models like IMD GFS, WRF, ECMWF, NCMRWF NCUM, GEFS and various international models are utilized for this purpose. The digitized decision support system known as SYNERGIE was utilized for decision making and for development of consensus forecast.

Compiled by: Krishna Mishra & Naresh Kumar.