Why Monsoon Surge Is Weak Over Kerala, Rainfall Deficit Becoming Large

Kerala is one of the rainiest states during the southwest monsoon. June contributes nearly 1/3^rd of the season’s rainfall with an average of 648.3mm during the month. The month is at par with July and together, they contribute 2/3^rd of seasonal rainfall. Any growing deficiency in the month of June becomes difficult to catch up, at later dates. Though, these are still early days there are a few factors to start with for the sluggish start.

-No monsoon system has formed over the Bay of Bengal after the onset of monsoon. There is a cyclonic circulation over the Gulf of Martaban and the Northeast Bay of Bengal. However, it may not lead to the formation of any low pressure. It is likely to keep its distance from the Indian Coast and may not strengthen the surge along the West Coast. The system will push the rains over Northeast India, later next week. To accentuate monsoon activity over Kerala, the formation of low/depression at the earliest is considered essential. 

-The cross-equatorial flow over the tropical Indian Ocean and South Arabian Sea remains weak.  Accordingly, the westerly stream of monsoon along the Kerala-Karnataka coastline is not strong enough to speed up equitable monsoon bursts over the region.

-Weak cross-equatorial flow has led to the absence of a ‘low-level westerly jet’ off Sri Lanka, Maldives and the Southeast Arabian Sea. The Strength of the jet is the decisive factor for intensifying rainfall, all along the coast and interiors of Kerala.

-No offshore vortex has formed in the Arabian Sea, in the proximity of Lakshadweep Islands and the extreme southeast Arabian Sea. Even a small-scale vortex, off Kerala, moving northward along the coast can fetch decent rains. Though, such incidents are not very frequent but can fill the gaps over scanty rainfall pockets.

Last year, the state of Kerala had recorded a shortfall of nearly 60 % rainfall in the month of June.   Rainfall became further scanty in August and it was near drought for the state with a large deficit of 87% rainfall. Despite some recovery in September, which registered a surplus of 53% rainfall, the season as a whole, ended with a huge deficiency of 34%.

Monsoon surge is likely to go weak for the state and neighbourhood, during next week. There is no likelihood of any strong system coming up over the Bay of Bengal. The Favourable situation may not develop even in the Arabian Sea. Accordingly, the shortfall over the state may grow further.

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