Close to a fortnight after its onset, the progress of the monsoon has been on par over the South Peninsula and southern fringes of Central India. But there is a lag over East India, and it may end up fairly far away from Bengal, Jharkhand, Bihar and East Uttar Pradesh where it should ideally reach by today.

Slowing down

India Met Department (IMD) has gone on record saying that the progress of monsoon may slow down after current expansive phase loses steam over the next couple of days. The weak phase would extend until June 20 according to indications, beyond which forecasts are not available with respect to formation of sea-based systems to fuel the monsoon.

An ensemble model of the US National Centres for Environmental Prediction had pointed to the possibility of a fresh low-pressure area taking shape in the Head Bay of Bengal after June 20. But it is not persisting with it anymore, at least with respect to the strength of the system, though it points to possibility of rains persisting over East India during this phase.

The next monsoon-friendly Madden-Julian Oscillation (MJO) wave may not be in before June 29. So the seasonal rain activity may stay suppressed until then, according to indications.

Trough over North

The MJO wave helps with formation of low-pressure areas/depression leading to monsoon onset or revival. The next MJO phase would likely extend from June 29 to July 14. Meanwhile, an East-to-West trough across the plains from North-West to East India, essentially a pre-monsoon feature, has been bringing thundershowers and lightning to the region.

A 'low' with its base over the Head Bay would have fanned monsoon easterlies into the trough to bring seasonal rains into the region. But the location of the current one, over North-East Bay and adjoining Bangladesh coast, doesn't allow this process to happen to the full extent.

This is now forecast to become more 'marked' and intensify into a depression later today. Its location and bearing though may not bring in gains to Indian territory as was earlier thought. Instead, Myanmar, Bangladesh and, to some extent by turn, the North-Eastern States of India, are expected to benefit the most from the 'low' initially.

Pacific storms

The European Centre for Medium-Range Weather Forecasts suspects that a weakened 'low' may retrace its track to Indian territory, but die out soon after. It also indicates that storm activity in the North-West Pacific may pick up, with most of them heading way East or North-East, which doesn't help the Indian monsoon.

As of yesterday, the monsoon has covered Thane, Mumbai (early by a day) Ahmednagar, Parbhani, Yeotmal, Brahmapuri, Rajnandgaon, Bhavanipatna, Puri, Agartala, Lumding, and North Lakhimpur. It had entered most parts of Konkan, some more parts of Madhya Maharashtra, Marathawada, Vidarbha, Chhattisgarh and Odisha.

It should be able to enter more parts of Chhattisgarh and Odisha; parts of Bengal and the remaining parts of the North-Eastern States during next two days. The current pace of its progress should take it to some more parts of Bengal, Odisha and parts of Jharkhand and Bihar during the subsequent two days (by June 15).

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