The systems in Bay of Bengal along with Monsoon Trough are main drivers of the advancement of Monsoon, also being major contributors of core Monsoon rains.
There are depressions that form in the Bay of Bengal, Arabian Sea and in land, known as insitu. Bay of Bengal has more frequent systems that the Arabian Sea with the ratio being 4:1. As the Monsoon months progress, systems increase with maximum systems forming in September, and lowest in June.
The insitu systems also intensify on land under the influence of a westerly trough or Western Disturbance with their ratio in terms of Bay being 1:6.
Monsoon depressions have a typical characteristic in terms of weather distribution. Southern half sees more rains as compared to the northern with the most amount of weather being in the southwest region.
June depressions which are responsible for advancement and progress of Monsoon, are different than the systems that develop during the thick of Monsoon. Withdrawal month systems are also different from typical Monsoon systems.
The systems in the Bay form in the Northern parts or as we can call it, the head Bay in the beginning, and as the season progresses, shift slightly south over the northern parts of Central Bay of Bengal.
June systems in Bay have coastline on either side, and do not have much pace due to which these systems do not intensify much. The systems that develop later in the core Monsoon months get more oceanic area making them more significant and helping them in gaining strength.
The tracks of the systems also varies, and with the Northern Limit of Monsoon being dictated by the track and movement of the Monsoon system developing in June. Similarly, the withdrawal line is dictated by the systems’ track forming in September.
Every month, on an average at least two systems are seen in the Bay of Bengal and anything less than two systems were deficit in terms of Monsoon systems for Bay.
However, this year, the first Circulation has come up in the Bay of Bengal which is taking shape now. The system is now likely to form a Low Pressure Area on June 20. While this system will remain feeble but will be responsible for carrying Monsoon further into central, eastern as well as southern parts.
Image Credit: India Today
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