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The southwest monsoon has progressed further northwards into the Bay of Bengal, covering the whole of Andaman and Nicobar Islands and advancing towards Myanmar, said The India Meteorological Department (IMD) on May 30, 2023.
The progress comes after a significant delay. On May 19, the IMD had initially declared that the southwest monsoon would pass over the northernmost tip of the Andaman and Nicobar Islands and move towards Myanmar (the trajectory shown in the graphic below) by May 22. But the actual onset has been delayed by at least eight days.
Even though IMD had predicted the onset of monsoon in Kerala by June 4, with an error margin of four days, a 12-day stalling looks significant.
The climate experts Down To Earth spoke to suspect the stalling is connected with Typhoon Mawar, which has rapidly intensified in the Pacific Ocean and is moving towards Taiwan and China in the South China Sea.
The experts agreed that the typhoon — which started forming around May 20 — has played a role in the slow progress. But its exact role remains a point of contention.
Raghu Murtugudde, professor of atmospheric and oceanic science at the University of Maryland, cited two reasons for the stalling of the monsoon.
“There was a cyclone spinning just to the south of the equator and that was disrupting the cross-equatorial winds till about a week ago,” Murtugudde said.
Now the massive typhoon in the Pacific is sucking the winds right into the Pacific across the Bay of Bengal and the South China Sea. This has blocked the monsoon trough from moving northwestwards over to the Bay and India. In fact, the trough arrived over Andaman and Nicobar on time around mid-May and then got stuck, he added.
A trough is “an elongated area of relatively low atmospheric pressure,” according to the National Oceanic and Atmospheric Administration.
Once the typhoon makes landfall and slows down, the winds over the North Indian Ocean “will be free to get back to their monsoon business”, Murtugudde said.
However, according to Akshay Deoras, a climate scientist at the University of Reading, UK, the hiatus is common. “This is a common feature after a tropical cyclone propagates (Cyclone Mocha) over the Bay of Bengal,” Deoras said.
While both experts are of the view that the typhoon has sucked the winds out of the Indian Ocean and propelled it towards the Pacific Ocean, it is at this point that their views diverge.
Murtugudde said the typhoon sucking the wind had created a blockage or a barrier for the trough to move northwestwards into the Bay of Bengal and India.
On the other hand, Deoras said the typhoon has played a role in the strengthening of monsoon winds over the Bay of Bengal by sucking the wind in its direction.