Why did cyclones give October a miss?

Context

• This year, October passed without witnessing a cyclonic storm.

Key points

• October to December period is among the favourable months for the development of cyclones in the Bay of Bengal and the Arabian Sea.
• India’s east and west coasts are prone to cyclones with the maximum associated hazards such rain, heavy winds and storm surge.

Cyclonic disturbances

• Cyclonic disturbance occurs either in the form of a well-marked low pressure, depression or a deep depression.
• It is weather systems with varying wind intensities ranging from 31 – 61 km/hrformed either over sea or land, and are common in October.
• Ocean disturbances enter the Bay of Bengal from the South China sea side and head towards the Indian coast.

Reasons behind no cyclone in October

• IMD officials have attributed it to the weak La Nina conditions along the equatorial Pacific Ocean.
• Cooler than normal sea surface temperatures over this region, termed as La Nina, has been prevailing since August this year.
• Madden Julian Oscillation (MJO) was positioned in a favourable phase, the low-pressure systems intensified maximum up to a deep depression.
• There was the high wind shear noted between the different atmospheric levels, last month.
• The vertical wind shear created due to significant wind speed difference observed between higher and lower atmospheric levels prevented the low-pressure systems and depression from strengthening into a cyclone.
• MJO is kind of an eastward-moving cyclic weather event along the tropics that influences rainfall, winds, sea surface temperatures and cloud cover. They have a 30 to 60-day cycle.