NLM is directly related to the onset and advance of Monsoon. The term NLM starts flowing right from the onset to the withdrawal of Monsoon.
Southwest Monsoon normally sets in over Kerala around June 1. It advances northwards, usually in surges, and covers the entire country by July 15.
The western arm of the Monsoon line generally makes a quick advancement in the initial phase. After its onset, the NLM crosses Mumbai and reaches Dahanu by June 10. During this time the eastern arm covers only Northeast India. The slowest advancement is over west Rajasthan. It normally takes about 12 days for the Monsoon current to reach west Rajasthan, after its onset over Delhi on June 29.
Monsoon 2015
The NLM has already advanced into southern parts of south Arabian Sea, Maldives-Comorin areas and some more parts of southwest Bay of Bengal. This year the onset of Monsoon over Mumbai and Kolkata is likely to be delayed by one week. The NLM will reach Delhi around July 2-4.
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Though the Monsoon current does not appear strong enough, existing cloud pattern and pre-Monsoon activity in Peninsular India suggest that Southwest Monsoon will arrive shortly over Kerala, around the scheduled date.
Featured image courtesy- no-mad.in