Northeast Monsoon Waits in the Wings: Onset Pending Withdrawal Of Southwest Monsoon

Key Takeaways:

• Southwest Monsoon withdrawal is likely to be completed across India by October 15, 2026.
• Northeast Monsoon onset follows the retreat of Southwest Monsoon, with October 20 considered the normal onset date.
• Persistent southeasterly winds, deep easterly flow and widespread coastal rainfall are key indicators of Northeast Monsoon onset.
• Tamil Nadu receives nearly 48% of its annual rainfall during October–December, making Northeast Monsoon its principal rainy season.
• Forecast Validity: October 8–20, 2026.

Southwest Monsoon is in retreat mode and has already withdrawn from the northern, western and most central parts of the country. It is likely to vacate the remaining southern and central parts during the next 2–3 days. The monsoon stream may extend its stay over the eastern and northeastern parts till 14th October, and complete withdrawal from the country is likely by 15th October. This will clear the way for the onset of Northeast Monsoon over the South Peninsula.

The two individual monsoon streams do not coexist over the Indian subcontinent. At best, the withdrawal of Southwest Monsoon and the onset of Northeast Monsoon could be simultaneous. This has happened in the past on a few occasions. The onset of Northeast Monsoon is not declared before 10th October, even if conditions become favourable. The criteria for the arrival of the winter monsoon include the following:

- The withdrawal line of Southwest Monsoon reaches 15°N over the South Peninsula, with complete withdrawal from other parts of the country.

- Onset of persistent southeasterly winds over the Tamil Nadu coast.

- Depth of easterly winds up to 5,000 feet or more.

- Fairly widespread rainfall over Coastal Tamil Nadu and South Coastal Andhra Pradesh.

As per statistical records, the normal date for the onset of easterly/southeasterly winds is 14th October. Based on the long-term average, the normal date of Northeast Monsoon onset is 20th October. However, there have been occasions when the onset was delayed until November, such as in 2018 (1st November), 2000, 1992 and 1988 (2nd November). In 40 out of the last 50 years, the onset has occurred on or after 15th October. On half of these occasions, the onset was delayed until 25th October or later.

For record purposes, the Northeast Monsoon is confined to only five subdivisions, namely Kerala, Tamil Nadu, Coastal Andhra Pradesh, Rayalaseema and South Interior Karnataka. However, rainfall activity may even extend to most other parts of the South Peninsula. Northeast Monsoon is the chief rainy season for the state of Tamil Nadu. Nearly 48% of the state's annual rainfall occurs during the October–November–December quarter. Kerala and Tamil Nadu are the rainiest pockets during the winter monsoon, with each state having normal seasonal rainfall of 450 mm to 500 mm. Occasionally, Northeast Monsoon activity extends beyond the stipulated October–November–December period, but the seasonal rainfall count remains between 1st October and 31st December for record purposes.