Context: The northeast, or winter, monsoon has ended on a high, with an overall surplus rainfall being recorded for the season.

The year that just went by witnessed the rare meteorological coincidence of the northeast (winter) monsoon making its onset on the same day as the southwest monsoon withdrew officially.

What is the northeast (winter) monsoon?

Though much less heard of, especially in the north of the country, the northeast monsoon is as permanent a feature of the Indian subcontinent’s climate system as the summer monsoon.

The India Meteorological Department (IMD) recognises October to December as the time for the northeast monsoon.

During this period, rainfall is experienced over Tamil Nadu, Kerala, and Andhra Pradesh, along with some parts of Telangana and Karnataka.

 Difference between Northeast and Southwest monsoons?

The Northeast monsoon derives its name from the direction in which it travels — from the northeast to the southwest.

Similarly, the summer monsoon moves in exactly the opposite direction — from the southwest to the northeast. That is why it is called the southwest monsoon.

When does the northeast monsoon set in?

Although October, November, and December are supposed to comprise the northeast monsoon season, the rains normally set in only around October 20.

The southern peninsular region receives rain in the first half of October as well, but that is attributable to the retreating summer monsoon.

• The summer monsoon season ends on September 30 but the withdrawal does not happen overnight.
• The southward withdrawal takes place over a period of three to four weeks. It usually starts around the second week of September and continues till about the second week of October, bringing rain as it retreats.

Where does it rain during the northeast monsoon season?

The northeast monsoon brings rain to just five of the 36 meteorological divisions in the country — Tamil Nadu (which includes Puducherry), Kerala, Coastal Andhra Pradesh, Rayalaseema and South Interior Karnataka.

As such, this season contributes only 11 per cent to India’s annual rainfall of 1,187 mm, compared to about 75 per cent in the summer monsoon season (the remaining rain comes in other non-monsoon months).

Impact on northern states:

Many other parts of the country, like the Gangetic plains and northern states, also receive some rain in November and December but this is not due to the northeast monsoon.

It is caused mainly by the Western Disturbances, an eastward-moving rain-bearing wind system that originates beyond Afghanistan and Iran, picking up moisture from as far as the Mediterranean Sea, even the Atlantic Ocean.

In the higher reaches of Jammu and Kashmir, Himachal Pradesh, and Uttarakhand, the precipitation is often in the form of snow.