OCTOBER STORM

1. Context

2. Why Storms in October 

• October-November and May-June see storms in the North Indian Ocean comprising the Bay of Bengal and the Arabian Sea with an average of five deploying in a year. 
•  In the past 131 years, October saw 61 storms in the Bay of Bengal, as per the Regional Specialised Metrological Centre (RSMC).
• The east coast notably Odisha has faced many of its severest storms in October including the Super Cyclone of 1999.

3. Ocean-atmospheric factors 

• After the withdrawal of the Southwest monsoon, there is a rise in ocean heating, which leads to a rise in sea surface temperatures over the Bay of Bengal. The atmospheric moisture availability over the ocean is higher.
• So, when remnant systems from the south china sea reach the Bay of Bengal, they get conducive conditions aiding the formation and intensification of Cyclones in October.
• In recent years ocean-atmospheric factors hinder this phenomenon.
• For instance, in 2020, weak La Nina along the equatorial Pacific ocean prevented a cyclonic formation near India's coast.

4. Cyclone Sitrang 

• On Thursday IMD officials said the cyclonic storm will reach close to the coasts of the West Bengal-Bangladesh by October 25.
• The name Sitrang will be given by Thailand and feature in the list of Tropical cyclone names prepared by the RSMC been followed since April 2020.

5. States like to be affected 

• The IMD is yet to release the probable cyclone track, but as per the latest updates, the Prevailing low-pressure system will strengthen and move towards India's east coast in the coming four days.
• Gale winds and enhanced rainfall are expected mainly over Andaman and Nicobar islands, Odisha, West Bengal and Bangladesh, particularly the Coastal Districts.

6. Weather models

• Weather models on Thursday suggested that the low-pressure system (Wind speed of 31 km/hr) will strengthen into a depression (Wind speed of 31 to 50km/hr) by October 22 and further into a deep depression (Wind speed of 51-61km/hr) by October 23.
• Thereafter, it will most likely re-curve northeastwards, thus skirting past the Odisha coast.
• As it progresses, it will intensify into a cyclonic storm (windspeed of 62-87 km/hr) by October 25.
• The storm is expected to reach close to the West Bengal and Bangladesh coasts in the north Bay of Bengal on October 25.
• Winds with speeds ranging between 40-45km/hr gusting to 55 km/hr are likely over the Andaman Sea and Andaman and Nicobar islands on Friday.
• Here, light to moderate rainfall (15.6 to 64.4 mm in 24 hours) will continue till Saturday.
• As the storm is expected to come close to Odisha shores, heavy to very heavy rains (64.5 to 204.4 mm in 24 hours) Would lash over Puri, Jagatsinghpur and Kendraparha districts during October 22-25.
• The IMD has issued a "yellow" for these coastal districts. Districts along the Gangetic West Bengal, too, will experience moderate rainfall accompanied by lightning on October 24 and 25.

• In comparison with the Bay of Bengal, only 32 storms have developed in the Arabian Sea in October since 1891.
• Climatologically too, the IMD states that of the five storms formed in the North Indian Ocean in a calendar year, four are in the Bay of Bengal and one in the Arabian Sea.