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Season of Cyclones

Published: 16th Nov, 2023

Context:

Low pressure area forming mid-November expected to intensify into a depression & undergo rapid intensification.

Cyclones in Bay of Bengal

  • Two back-to-back low-pressure areas may be forming in the Bay of Bengal, both of which could further intensify into cyclones. One of them could also become a severe cyclone.
    • South Andaman Sea: The first low pressure area, induced by an upper air cyclonic circulation over the South Andaman Sea, the India Meteorological Department (IMD) shared. This system may gain strength to become a depression by mid-November.
    • Bay of Bengal: Another upper air cyclonic circulation has formed over the south-western parts of the Bay of Bengal. This may also induce a low-pressure area.
  • Fujiwhara Effect: The simultaneous formation of the second low-pressure area could lead to its interaction with the earlier system. Such an interaction is known as the Fujiwhara effect.

About Fujiwhara Effect:

  • When two ocean storms (storms, cyclones, hurricanes or typhoons) have formed in the same region, are spinning in the same direction and pass close enough to each other, “they begin an intense dance around their common centre”, according to the National Weather Service (NWS) of the National Oceanic and Atmospheric Administration, United States.
  • If one of the storms is a lot stronger and bigger than the other, the smaller one will revolve around the bigger one and “come crashing into its vortex to be absorbed”.
  • Two storms closer in strength can gravitate towards each other until they reach a common point and merge, or merely spin each other around for a while before shooting off on their own paths. In rare occasions, the effect is additive when the hurricanes come together, resulting in one larger storm instead of two smaller ones,” according to NWS.

The Storm situation in India:

  • Unlikely of Fujiwhara Effect: The second low-pressure area will likely form after the dissipation of the first system so the possibility of them interacting under the Fujiwhara effect is not much.
  • According to Down to Earth, both the low pressure areas could intensify into cyclones with the earlier system also possibly intensifying into a severe cyclone.
  • The low pressure area forming today earlier would intensify into a depression and undergo rapid intensification (RI).
    • Rapid intensification: RI occurs when a tropical cyclone gains wind speeds of 56 kilometres per hour or more in a span of 24 hours. RI generally makes it difficult for weather agencies to predict the track and intensity of tropical cyclones.
  • Recent cyclone studies: Many recent tropical cyclones have undergone RI, which is mainly due to warmer-than-usual sea surface and subsurface temperatures. For instance, cyclone Freddy in February-March 2023 became the first tropical cyclone ever to experience seven phases of rapid intensification over its lifetime.
  • Cyclone Freddy: The cyclone had its genesis near Australia and moved all across the southern Indian Ocean to devastate Madagascar, Malawi and Mozambique.
  • Cyclone Biparjoy: Cyclone Biparjoy in the Arabian Sea in June 2023 also showed RI.

Threat of cyclones on Indian Coasts:

  • While the threat of the Fujiwhara effect is far off, back-to-back cyclones with RI in tow could create considerable impacts along the Indian coasts.

Verifying, please be patient.

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