Low Pressure in Bay of Bengal, the first step towards Northeast Monsoon

A Low Pressure in Bay of Bengal has formed near Andaman Islands yesterday.  It is expected to intensify into a Well Marked Low over the next 24 – 48 hours.  As we had mentioned a couple of days back in our post one of the key triggers for the change of winds from Westerlies to Easterlies or vice versa is the forming of a tropical disturbance in Bay of Bengal.

The overall macro mechanisms of the monsoons are driven by the Power houses present a few thousand kms away Mascarene High near Australia for Southwest Monsoon & Siberian High over Eurasia for Northeast Monsoon.  But the change of wind directions is an important trigger which is done at the local level at North Indian Ocean.  This important climatology event during the Summer months in the form of a Pre Monsoon disturbance to set things on course for the Southwest Monsoon over the Indian Sub Continent. Similarly post monsoon disturbance changes the wind regime from Westerlies to Easterlies paving way for the onset of Northeast Monsoon.


As one can observe from the chart it is a David vs Goliath battle between Haima, the typhoon in West Pacific and the Low Pressure in Bay of Bengal.  On the face of it looks an uneven battle with the Low Pressure in Bay of Bengal standing no chance against the Goliath in West Pacific.  But over the next couple of days with the Typhoon nearing the China conditions become more favorable for the Low Pressure in Bay of Bengal to develop its own steam and reduce the cross equatorial flow to its bigger cousin. We could see this disturbance develop into possibly a Depression or possibly with some quick change in dynamics into a marginal cyclone as well which can never be ruled out with post monsoon disturbances.

It would make sense to take 48 hours at a time and see how this Low Pressure in Bay of Bengal evolves but one thing which we could be assured is the trigger for Northeast Monsoon onset has been put in action.