No. IV-18.4 - (IMD), Pune

1. Introduction
1.1 October to December is the major period of rainfall in south Peninsula,
particularly the eastern half, comprising of the meteorological sub-divisions of.
Coastal Andhra Pradesh, Rayalaseema and Tamil Nadu. In Tamil Nadu, this is the
main rainy season accounting for nearly 60% of the annual rainfall in the
coastal districts, and about 40% to 50% in the interior districts of the state.
Though the principal rainy season for South Interior Mysore, Kerala and Arabian
Sea Islands is the southwest monsoon, still rainfall continues till almost
December in these sub-divisions, the period October to December contributing
about 20% of the annual total. In Rayalaseema, September and October are the
rainiest months, contributing 36% of the annual total.
1.2 The term "Northeast Monsoon" is often used to describe the period
October to December. However, according to the departmental classification of
the year into seasons, these three months constitute the "Post-Monsoon season";
it is also known as "the Retreating Southwest Monsoon Season". As early as 1886,
Blandford, in his Memoirs on "Rainfall of India", has raised the question about
the term, 'Northeast Monsoon Rains'. He says "........it is hardly correct to
speak of the Carnatic rains as those of the Northeast Monsoon, in as much as the
rainfall ceases as soon as the monsoon is established down to Ceylon. It falls
only so long as the region in question is within or on the borders of the barometric
depression towards which the winds blow, not from the north only, but
also from east, southeast, and other quarters
". Though the term
'Northeast Monsoon' has been in use for a long time to describe the rainfall
season of the southeast Peninsula, the appropriateness of the term has often
been discussed. As recently as 1972, the topic came up for discussion in the
Seventh Conference of Forecasting Officers, which was in favour of the retention
of the term and recommended*that "the term Northeast Monsoon should continue to
be used for rainfall season over south Peninsula during middle October to
December".
* This recommendation is under examination.