Monsoon Express is running on time

So far, the monsoon has progressed on expected lines, she says. But its advance over central India and the regions of Jharkhand, Bihar, Chhattisgarh, Orissa, Rajasthan, Madhya Pradesh and the adjoining states is entirely dependent on a couple of critical factors.

First, there has to be a formation of a low pressure monsoon trough oriented in a west, north-westerly direction and moving from Kolkata to Ganganagar — in addition to the formation of a depression over Bay of Bengal.

Secondly, the intensity of the ‘‘heat-low formation’’ (caused by a fall in pressure due to intense heating of the landmass during summer) over north-west India, including Rajasthan and parts of adjoining Pakistan, is critical and necessary.

‘‘We are monitoring a few weather models and hope things turn out as expected,’’ says Jayanthi. Unlike this year when the monsoon arrived over the mainlands almost 15 days early, the normal onset is expected around June 1 when it hits Kerala, parts of Tamil Nadu and the north-eastern states of Meghalaya, Tripura and Manipur.

This advances further to Karnataka, Andhra Pradesh and Assam on June 5 and Maharashtra, parts of Chhatisgarh, Orissa, West Bengal, Bihar and Jharkhand on June 10. It then moves to Gujarat, Madhya Pradesh and Uttar Pradesh on June 15 and finally to the north-western states of Punjab, Haryana and Rajasthan around July 1.

This year though, the early onset is attributed to a cyclonic storm over the Bay of Bengal, triggering the monsoon circulation pattern. ‘‘Such a phenomenon is rare. Going by the past, we were initially sceptical and hence called it a temporary advance,’’ says Jayanthi.

India saw early monsoon twice — in 1960 and 1969 — and on both occasions, it was associated with a cyclonic storm over the Bay of Bengal.

‘‘However, the circulation was not sustained unlike this year when it has been behaving properly,’’ she adds.

While in 1960, the arrival of the monsoon was recorded on May 18, in 1969, it was on May 16 — though it was actually logged around June 15 for both years.

This year, ever since it reached the mainlands over Kerala and parts of Tamil Nadu on May 18, the monsoon has kept advancing steadily. It reached coastal Konkan and south Maharashtra two days ago—in between, covering Nagaland, Manipur, Mizoram, Tripura, parts of Assam, Meghalaya and Arunachal Pradesh around May 21. ‘‘This too, was two weeks ahead of schedule,’’ says Jayanthi.

On May 23, the monsoon advanced to coastal south interior Karnataka and parts of Tamil Nadu, entire Assam and Meghalaya and steadied for the following one week. By June 1, it had advanced to interior Karnataka, Rayalseema and the entire south sub-Himalayan West Bengal.

Finally, it reached Maharashtra, i.e., coastal Konkan, and Telangana on June 5-6, which is ‘‘almost on normal time’’.