Context: According to the Indian Meteorological Department (IMD), Cyclone Michaung is expected to make landfall near Bapatla district of Andhra Pradesh at around 12 pm on December 5. 

Cyclone Michaung: Red Alert, Landfall Projections, and Devastating Impact in Chennai

• Warning: Meteorological officials have issued a red alert to parts of the states of Tamil Nadu and Andhra Pradesh, which come on the path of Cyclone Michaung.
• Affected Areas: The Cyclone Michaung is likely to make landfall on the coast of Andhra Pradesh state between Nellore and Machilipatnam, close to Bapatla.
  • Currently, Cyclone Michaung  is north of the city of Chennai. This has resulted in heavy rains and gusty winds in the city.
• Catastrophic Impact in Chennai:  
  • Many areas in the city have been submerged. There has been massive loss of property due to water logging in residential areas.
  • The Chennai airport has been shut down due to excessive rains.
  • About six people have lost their lives, with the causes of death being falling structures and electrocution. 

Cyclone Michaung – From Tropical Storm to Severe Cyclone – Threats of Heavy Rains, Surges, and Flooding

• About: Michaung is a tropical storm, which is currently centred around 80 km southeast of Nellore and 120 km north-northeast of Chennai, and moving along Andhra Pradesh coast.

• Features:
  • IMD had predicted that Michaung would remain a ‘tropical cyclone’ (wind speeds between 62 kph to 87 kph) until it crossed the coast of Andhra Pradesh.
  • However, IMD upgraded it to the intensity of a ‘severe’ storm (wind speeds between 88 kph to 166 kph).
• Reason for Intensification: It is believed that Michaung was strengthened due to above-normal value of the heat index off the southern Andhra Pradesh coast.
• Warning Issued by IMD:
  • Heavy Rains: Rains accompanying the storm are expected to cause widespread crop damage to standing crops that are nearing harvest, as a result of extremely heavy rainfall.
  • Storm Surges: Storm surges and tidal waves are predicted as the cyclone approaches the coast. Strong winds with speeds of 90 kph to 110 kph may be experienced.
  • Flooding: The rains can also cause flash floods in low lying areas of the state of Andhra Pradesh.

Conditions and Occurrence of Tropical Storms in the Indian Ocean Region

• About: Also known as cyclonic storm or cyclone, tropical storm is a rapidly rotating low pressure system, which originates over tropical areas.
  • It is characterized by a closed low-pressure center, strong winds, and a spiral arrangement of thunderstorms that bring heavy rainfall along its edges.
• Conditions for formation:
  • Sea Temperature: A sea surface temperature must be higher than 27° C for formation of tropical cyclones.
  • Location: Tropical cyclones usually form between Tropic of Cancer and Tropic of Capricorn where the temperature is optimum.
  • Coriolis force: The cyclonic conditions require presence of the Coriolis force. Hence cyclones are formed away from the equator.
  • Vertical wind speed: The vertical wind speed must have small variations.
  • Upper divergence: A well developed divergence in the upper layers of the atmosphere will help in the rising of air currents within the cyclone, allowing low pressure to be maintained at the center.
  • High humidity: High humidity (around 50 to 60 per cent) is needed in the mid-troposphere for the formation of cumulonimbus cloud.
• Occurrence: On an average, about five cyclones develop in the North Indian Ocean region (the Bay of Bengal and the Arabian Sea) every year.
  • On an average, four cyclones develop over the Bay of Bengal and one over the Arabian Sea. However, Arabian Sea cyclones often reach higher intensities and can cause widespread damage.
• Most Suitable Time: The region is prone to cyclone development during the pre-monsoon (April-June) and post-monsoon (October-December) months.
  • Cyclones that form in May and November have the potential to reach higher intensities than storms that form at other times due to favourable conditions.
• Changing Situation: Storms that develop over the North Indian Ocean in December don’t usually attain destructive intensities due to unfavourable ocean conditions.
  • Hence, high-intensity cyclones such as Michaung are not common at this time of the year.

Factors Driving Tropical Storm Intensification: The Crucial Role of Ocean Heat and Beyond

• Role of Heat: Tropical cyclones are fueled by ocean heat, with temperatures of 26 degrees Celsius or more, prevailing at depths between 50 metres and 100 metres, being conducive for cyclogenesis.
  • Warm oceans contribute to a cyclone’s rapid intensification at sea. In this regard, Tropical Cyclone Heat Potential (TCHP) is considered an important factor in cyclone genesis, intensification, and propagation.
• Other factors: Apart from ocean heat, other factors such as boundary layers (the fluid layer adjacent to a bounding surface), wind shear (changes in wind direction and/or speed over a vertical or horizontal distance), convection (transfer of heat within a fluid), Rossby waves (which occur in rotating fluids), upper ocean circulation, and air-sea interaction have a major role in cyclone intensification.

Conclusion:

In recent times, Cyclonic storms do not follow a fixed pattern in terms of occurrence or intensity. This is due to events of climate change that are affecting global climatic conditions over both land and oceans.