Back-to-back weather systems are not uncommon in the Northeast Monsoon

Back-to-back weather systems have formed over the Bay of Bengal during the Northeast Monsoon like this year. But these systems mostly formed in October and November. A cluster of 15 cyclones occurred between 1961 and 2010. Similar incidents have occurred since 2011 as well, said a report published by the India Meteorological Department (IMD).

Citing his analysis on clusters of cyclonic storms forming in the Bay of Bengal and Arabian Sea regions, YEA Raj, former Deputy Director General of Meteorology, Chennai, said it was not an unusual occurrence during the northeast monsoon. However, the frequency of weather systems decreases in December, and they are less likely to intensify into cyclones at the end of the monsoon.

Sometimes, tropical cyclones form in the same basin in quick succession. Two cyclones or depressions forming eight days apart are called clusters, he pointed out.

This December, a low pressure area formed over the Bay of Bengal on December 7, a few days after Cyclone Fengal moved inland. After that, the current well-marked low pressure area formed over the Bay of Bengal. Between 1999 and 2010 there was a break from such events.

Mr. Raj recalled that in 1966 there were two separate tropical cyclones along with four tropical cyclones in the Bay of Bengal. Two of them intensified into cyclonic storms in the first week of November 1966, the other two cyclones gained strength between November 19 and November 27 and formed a cluster.

Recalling another cluster, he said that in the first fortnight of November 1992, there were three consecutive tropical cyclones in the Bay of Bengal, but there was no cluster of cyclones in the Arabian Sea. It is mentioned in the report that there are favorable conditions for the formation of cyclone clusters only in the Bay of Bengal. “There were four cluster events in 2013, 2016, 2020 and November 2021 in 13 years from 2011. It also includes depression and cyclonic conditions,” Mr. Raj added.

The life cycle of a weather system spans five days — from low pressure areas to cyclonic storms. Similar instances may occur in low pressure areas, as the IMD has documented tracks from depressions and cyclonic phases. The center of a weather system cannot be defined in a low pressure area as in a dense system, he added. The analysis was conducted as part of IMD’s Meteorological Monograph on ‘Meteorologically Based Forecasting of Tropical Cyclones in the Indian Ocean’.