Southwest Monsoon is likely to withdraw completely around middle of next week. Simultaneously, the Northeast Monsoon shaping up presently over Andaman Sea and Bay of Bengal is likely to come along shore of Tamil Nadu. Though, this withdrawal and onset is an annual event, but simultaneous occurrence will just be a coincidence.
Also, this will be for 3rd consecutive year and nearly matching with 2020, when the withdrawal and onset harmonized on 28thOctober. In 2019, the withdrawal was achieved with military punctuality on 16thOctober against the normal date of 15thOctober and the onset of Northeast Monsoon the same day, a bit earlier than its normal date of 20thOctober.
Southwest monsoon commenced its withdrawal this year behind the scheduled timeline of 17thSeptember. It started on 06thOctober from West Rajasthan and vacated completely North India and few parts of Central region by 11thOctober. Subsequently, formation of series of weather systems over Bay of Bengal and Arabian Sea delayed the process.
In addition to few parts of South India, it still hangs around over some parts of Northeast India, West Bengal and Odisha. In view of clearance of weather activity, the retreat of monsoon from these parts is likely to be over in the next 2-3days.
The left over portions of Karnataka, Telangana, Andhra Pradesh, Bay of Bengal and Arabian Sea will follow suit in the subsequent 3days. Southwest monsoon is expected to wind up completely by 26thOctober, with a delay of about 11days. The process is considered complete when the withdrawal line reach 15°N over South Peninsula.
Northeast monsoon is not declared before 10thOctober even if the specified conditions prevail. Setting up of Easterly/ Southeasterly winds over South Bay of Bengal and coastline of Tamil Nadu is a pre requisite for onset of South India monsoon.
In view of likely establishment of easterly winds over Bay of Bengal and Southeast Peninsula in the lower levels of atmosphere, the Northeast monsoon is expected to open inning on 26th October, with a margin error of +/- one day. The normal date of onset of Northeast Monsoon is 20thOctober with a standard deviation of one week. Northeast monsoon is likely to make an explosive start for Tamil Nadu in general and the capital city Chennai in particular.