Northeast Monsoon

The period October to December is referred to as Northeast Monsoon season over peninsular India. Earlier this period was also referred to as "Post-Monsoon Season" or "Retreating southwest Monsoon Season".

Northeast Monsoon season is the major period of rainfall activity over south peninsula, particularly in the eastern half comprising of the meteorological subdivisions of Coastal Andhra Pradesh, Rayalaseema and Tamilnadu-Pondicherry. For Tamilnadu this is the main rainy season accounting for about 48% of the annual rainfall. Coastal districts of the State get nearly 60% of the annual rainfall and the interior districts get about 40-50% of the annual rainfall.

Though the principal rainy season for Interior Karnataka, Kerala and Lakshadweep is the Southwest Monsoon season, rainfall continues till December in these sub-divisions, the period October-December (Northeast Monsoon ) contributing about 20 % of the annual total.

The increase in rainfall activity over Andhra-Tamilnadu coasts which takes place sometime around middle of October is generally considered as the "setting in of Northeast Monsoon". Normal date of onset of the northeast monsoon is around 20 October with a deviation of about a week on either side.

The rainfall over south peninsula towards the end of southwest monsoon season is mainly in the interior districts and it generally occurs in the afternoon , evening or early part of the night. As the season advances the rainfall is mainly in the coastal districts with the interior districts getting less rain. It generally occurs during night and early morning hours . Maximum rainfall mostly occurs between 2100 and 0300 hrs IST. Along the east coast rainfall during late night and morning hours (2400 to 0900 hrs) is an usual feature of northeast monsoon. When there is a low, depression or cyclone close by the rainfall occurs throughout the day.

Northeast monsoon rains occur in spells of about 3 to 4 days duration. Spells exceeding 4 days are much less (20%). There are at times long spells of dry weather with little or no rain.

http://www.imdchennai.gov.in/northeast_monsoon.htm

NORTHEAST MONSOON RAINFALL OVER CHENNAI
YEAR NUNGAMBAKKAM (NORMAL 75 CM) MINAMBAKKAM (NORMAL 77CM)
1990 97 77
1991 79 75
1992 73 75
1993 90 104
1994 118 115
1995 53 44
1996 126 113
1997 157 144
1998 72 80
1999 53 52
2000 40 50
2001 108 97
2002 99 83
2003 31 38
2004 57 62
2005 211 186
2006 89 96





NORTHEAST MONSOON RAINFALL OVER TAMILNADU
YEAR DATE OF ONSET SEASONAL RAINFALL (MM) ACTUAL SEASONAL RAINFALL (MM) NORMAL PERCENTAGE DEPARTURE (%)
1990 19 October 468 483 - 3
1991 20 October 488 477 + 2
1992 2 November 514 470 + 9
1993 21 October 784 479 + 64
1994 18 October 534 418 + 12
1995 23 October 260 479 - 46
1996 11 October 592 477 + 24
1997 13 October 810 478 + 70
1998 28 October 619 478 + 30
1999 21 October 517 483 + 7
2000 2 November 346 483 -28
2001 16 October 382 483 -21
2002 25 October 395 483 -14
2003 19 October 435 469 -7
2004 18 October 435 432 1
2005 12 October 773 432 79
2006 19 October 497 432 15