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Severe Cyclonic Storm 'Hamoon' Gathers Strength in Northwest Bay of Bengal

  • 26 Oct 2023

On 24th October, 2023, the Indian Meteorological Department (IMD) confirmed that the cyclonic storm 'Hamoon' has intensified into a severe cyclonic storm over the Northwest Bay of Bengal.

Key Points

  • North-eastward Movement: 'Hamoon' has been moving northeastwards at a speed of 18 km per hour in the past 6 hours.
  • It has now developed into a severe cyclonic storm, with its center located approximately 210 km east-southeast of Paradip (Odisha), 270 km south-southeast of Digha (West Bengal), and 350 km south-southwest of Khepupara (Bangladesh).
  • Anticipated Path: The cyclonic storm is expected to continue its nearly north-northeastward trajectory and is likely to make landfall on the Bangladesh coast, crossing between Khepupara and Chittagong around noon on October 25.
  • It is projected to hit as a deep depression.
  • Pre-emptive Measures: The Odisha Municipal Administration had issued an alert to all Urban Local Bodies (ULB) in anticipation of the formation of cyclonic storm 'Hamoon' in the Bay of Bengal.
  • ULB Chiefs were briefed about the potential hazards, which include heavy rainfall, strong winds, and adverse weather conditions posed by the cyclonic storm.

Cyclones- Overview

  • Cyclones are rapid inward air circulation around a low-pressure area.
  • In the Northern hemisphere, air circulates anticlockwise; in the Southern hemisphere, it's clockwise.
  • Cyclones bring violent storms and bad weather.
  • The word "Cyclone" comes from the Greek "Cyclos," meaning the coils of a snake, due to their appearance.

Classification

  • Two types of cyclones:
    1. Tropical cyclones
    2. Extra-Tropical cyclones (also called Temperate cyclones or Frontal cyclones)
  • The World Meteorological Organisation uses the term 'Tropical Cyclone' for systems with winds exceeding 'Gale Force' (at least 63 km per hour).
  • Tropical cyclones form between the Tropics of Capricorn and Cancer over warm tropical or subtropical waters.
  • Extra tropical cyclones occur in temperate and high latitude regions, sometimes originating in the Polar Regions.

Tropical Cyclones

  • Violent storms originating over tropical oceans, causing large-scale destruction with violent winds, heavy rainfall, and storm surges.
  • Among the most devastating natural calamities worldwide.
  • They develop over warm tropical oceans with conditions favoring formation:
    1. Large sea surface over 27°C.
    2. Presence of Coriolis force.
    3. Small variations in vertical wind speed.
    4. Pre-existing weak low-pressure area or low-level-cyclonic circulation.
    5. Upper divergence above the sea level system.

Stages of Formation - Tropical Cyclones

Formation and Initial Development Stage

  • Depends on transferring water vapor and heat from the warm ocean to the air, mainly through sea surface evaporation.
  • Results in the formation of massive vertical cumulus clouds due to convection and condensation.

Mature Stage

  • Intensification leads to vigorous thunderstorms and air rising in thunderstorms, spreading horizontally at the tropopause level.
  • Positive pressure at high levels accelerates downward air motion due to convection.
  • This induces subsidence, warm air compression, and the formation of a warm 'Eye' (Low-pressure center).
  • Characterized by concentric patterns of turbulent cumulus thundercloud bands.

Modification and Decay

  • Begins weakening as its warm moist air source diminishes or gets cut off (e.g., landfall or passing over cold waters).
  • Central low pressure, internal warmth, and high speeds decline.

Tropical Cyclones in India

  • Originates over the Bay of Bengal, Arabian Sea, and Indian Ocean.
  • Hits Indian coastal states, particularly Tamil Nadu, Andhra Pradesh, West Bengal, Odisha, and Gujarat.
  • Destructive elements:
    1. Strong Winds/Squall: Damages buildings, communication, trees, and causes loss of life and property.
    2. Torrential Rains and Inland Flooding: Spreads over a wide area, causing soil erosion and embankment weakening.
    3. Storm Surge: Abnormal rise in sea level inundates coastal areas, leads to drowning, erosion, vegetation destruction, and reduced soil fertility.