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Cyclone Asna

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Cyclone Asna

Context:

According to the India Meteorological Department (IMD) the deep depression that has been unleashing heavy rains over Gujarat is expected to intensify into a tropical cyclone, named Cyclone Asna, over the Arabian Sea on August 30.

 

More on News:

  • The deep depression, located 60 km northwest of Bhuj and 80 km northeast of Naliya on August 29, has been causing significant rainfall and flooding in Gujarat.
  • It represents the first cyclone formation in August in the North Indian Ocean (NIO) region since 1981, and the first in the Arabian Sea since 1976.
  • Cyclone Asna, named by Pakistan, represents a rare meteorological event, as only three cyclonic storms have been recorded in the Arabian Sea during August between 1891 and 2023.

Historical Context

  • 1976: The cyclone originated over Odisha, moved west-northwestward into the Arabian Sea, followed a looping track, and weakened near the Oman coast.
  • 1944: The cyclone intensified after emerging into the Arabian Sea before weakening.
  • 1964: A short-lived cyclone developed near South Gujarat and weakened near the coast.
  • In contrast, the Bay of Bengal has seen 28 cyclonic systems develop in August over the last 132 years.

Key Highlights:

  • IMD predicts it will move west-southwestwards, emerging into the northeast Arabian Sea off the Kachchh and adjoining Saurashtra & Pakistan coasts, and will intensify into a cyclonic storm.
    • It will then continue west-southwestwards over the northeast Arabian Sea away from the Indian coast in the subsequent two days and heading towards Oman.
  • Windy weather platforms indicate a clear eye of the cyclone and cyclonic wind speeds, supported by ECMWF and GFS data.
  • The formation and intensification of the current deep depression may be attributed to an unusual monsoon wind system.
    • Typically, the monsoon trough curving at its eastern end provides the necessary conditions for cyclone formation in the Bay of Bengal
    • This season’s shift in wind patterns, with strong easterly winds over southern India, has contributed to the development of the deep depression.
  • A deep depression has wind speeds between 52 kmph and 61 kmph, while Cyclone Asna has wind speeds ranging from 63 kmph to 87 kmph.

Scientific Insights

  • Previous beliefs suggested that soil moisture was a prerequisite for land-based cyclones. However, recent observations indicate that large-scale wind configurations may play a more crucial role.
  • Boreal Summer Intraseasonal Oscillation (BSISO): Transfers heat from the Indian Ocean to the Western Pacific Ocean, has contributed to the formation of the low-pressure systems (LPS) that evolved into the deep depression.
    • Instability in the atmosphere likely fueled deep convective storms, supporting the depression’s growth.

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