Monsoon onset over Kerala delayed : IMD

Monsoon onset over Kerala delayed : IMD

Subject : Geography

Context : Monsoon is likely to hit India’s southwestern coast around June 3 instead of the regular onset date of June 1, the India Meteorological Department (IMD) said on Sunday.

Concept :

• The southwest monsoon was earlier expected to hit Kerala on May 31, but the IMD said that a cyclonic circulation along the Karnataka coast is halting its progress.

Onset of Monsoon

• The normal date of onset of the southwest monsoon over Kerala i.e. the first place of entry in the mainland of India is 1st June.
• The monsoons advance quickly accompanied with a lot of thunder, lightning and heavy downpour. This sudden onset of rain is termed as monsoon burst.
• Sometimes monsoons are delayed or they come much earlier than normal.
• Normally the onset occurs between 29th May and 7th June.
• The earliest onset was on 11th May in 1918 and 1955, while the most delayed onset was on 18th June in 1972.

The criteria for Onset of monsoon are:

• Rain-bearing westerlies being at a minimum depth and speed.
• At least 60% of the available 14 stations in Kerala and coastal Karnataka reported rainfall of 2.5 mm or more for two consecutive days after May 10.
• A certain degree of clouding, indicated by a parameter called ‘outgoing longwave radiation’ (OLR), being below 200 W/square metre.
• Currently, IMD’s own data indicated that except for the OLR, the other criteria were met. Thus, there is an element of subjectivity in arrival.