Unlike Southwest Monsoon, there is no official onset date for Northeast Monsoon as well as the Monsoon sets in one go over the region. The arrival of Monsoon is marked with the increase in rainfall intensity and spread beginning with Tamil Nadu and Andhra Pradesh.
Tamil Nadu has already started recording moderate to heavy rainfall, along with parts of Kerala. In fact, weathermen are of the view that prevailing weather situations are akin to what of the Northeast Monsoon.
However, onset of Northeast Monsoon is never attempted before the withdrawal of Southwest Monsoon from the entire country. Till now, Monsoon has only withdrawn from the parts of Central as well as few parts of South India. Normally, the season sets in around October 20, with an error margin of +/-5 days.
Northeast Monsoon that spans from October to December is major rainfall period for Southern Peninsula, particularly eastern half of the region. Tamil Nadu, Kerala, South Interior Karnataka, Rayalaseema and Coastal Andhra Pradesh are the main beneficiaries.
While Kerala and South Interior Karnataka record around 20% of its annual rainfall during the season, rest of the sub-divisions witness around 50% of its annual rainfall, with parts of coastal Tamil Nadu even recording 70% of rainfall.
Rainfall pattern would also undergo some changes as the rainfall that usually occurs during afternoon and late evening, would now be witnessed during night and early morning hours. However, if there is any system, we can expect rains all along the day.
Northeast Monson also coincides with the cyclone season for Arabian Sea and Bay of Bengal. In comparison between the two, Bay of Bengal is more active on account of series of systems forming in the ocean. All thanks to the active ITCZ (Inter Tropical Convergence Zone), which keeps on triggering disturbances in the sea. With Tamil Nadu and Andhra Pradesh having long coastlines, both the states remain more susceptible to rains during the entire Northeast Monsoon.
Meanwhile, frequency is less in Arabian Sea and until and unless a system forms closer to the West Coast, the likely region does not receive much rains. As per weathermen, wet spells during this season lasts for 3-4 days because weather systems are not very fast moving.
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