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Cloud parcels have started building along the West Coast, with the offshore trough marginally improving its reach from Kerala to South Maharashtra-Karnataka coasts by Monday evening.
Heavy convection was witnessed along the Karnataka and Goa coasts, even as some clouds drifted in a North-North-East direction towards East Madhya Pradesh, possibly bringing in some rain. The depth of the offshore trough, an elongated area of low-pressure and a receptacle for monsoon moisture mopped up over the Arabian Sea, is a proxy for the health and strength of the monsoon system.
It was far from being its healthiest self on Monday, best represented when it lies extended from the South Gujarat-Mumbai coast to the Kerala coast, signalling an active to vigorous monsoon.
Crucial Trough
The land-based trough, extending North-West to South-East from West Rajasthan to the Head Bay of Bengal determines the prospects for and performance of the monsoon over the northern half of India.
This crucial trough can form only after a proper low-pressure area materialises in the Bay of Bengal (ideally around the Head Bay) and crosses the coast and travels in a West-North-West direction.
Only after this can the northern limit of the monsoon get a move from where it is stuck currently - across Thane (including Mumbai), Ahmednagar, Buldhana, Amravati, Gondia, Titlagarh, Cuttack, Midnapore, Goalpara, and Baghdogra.
Delayed in the North
The monsoon is already three days behind schedule over a good part of the northern half of the country, including Gujarat, Madhya Pradesh, Odisha, Chhattisgarh, Jharkhand, Bihar and East Uttar Pradesh.
Formation of a helpful circulation in the Bay (whether deep enough to be a ‘low’ or not) is being indicated only after June 25, or better still, by June 27, when winds fall into a pattern off the Odisha-Bengal coast.
This in turn depends on the arrival of a Madden-Julian Oscillation (MJO) wave, whose next spell is shown to wield influence over the Arabian Sea and the Bay from June 27 to July 7.
The wave would return only by July 22, according to global model outlook, which would mean that a lull phase could be in the offing during July as well. But these are early model look-ins and would need to be verified in real-time.
When in the ‘normal’ position, the troughline in the North passes through Ganganagar (Rajasthan), Allahabad (Uttar Pradesh) and Kolkata (Bengal) before dipping into the ‘low’ over Head Bay. The ‘low’ will attract strong winds from the Arabian Sea which will be blocked by the Western Ghats, strengthening the offshore trough.
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