Keralam braces for northeast monsoon after 28% southwest monsoon deficit

After a deficient southwest monsoon season, which was 28% deficient in Keralam, the stage is set for the onset of the northeast monsoon over the State and the southern peninsula, with mixed prospects for rainfall. A marked shift in wind direction from westerlies to easterlies has already occurred, and the India Meteorological Department (IMD) is expected to announce the onset within the next 24 hours, with the prescribed criteria having almost been met.

Speaking to The Hindu, Neetha K. Gopal, Director, IMD, Thiruvananthapuram, said the withdrawal criteria for the southwest monsoon are expected to be fulfilled by October 15, paving the way for the simultaneous onset of the northeast monsoon. Persistent surface easterlies have been established, triggering rainfall over the southernmost parts of Tamil Nadu. By Thursday (October 15, 2026), the rain is expected to spread to other parts of Tamil Nadu, including the entire coast, as well as adjoining areas of Andhra Pradesh, marking the onset of the two-and-a-half-month northeast monsoon season over southern India, including Keralam, she said.

The onset is expected to bring a decent opening spell of rainfall to Keralam, aided by circulations over north Keralam and neighbouring Karnataka as well as the systems in the Bay of Bengal.

The IMD has issued an orange alert for Pathanamthitta, Kottayam, Idukki and Ernakulam on Thursday, warning of intense heavy rainfall and a yellow alert for the remaining districts, except Kannur and Kasaragod, for isolated heavy rain. Rainfall activity is expected to be more pronounced during the afternoon and night, with light to moderate showers likely during the rest of the day.

Although a decent spell of rain is expected in October, the formation of cyclones over the Bay of Bengal towards the end of October and in November remains uncertain. Climatologically, more weather systems tend to develop over the Bay in November, boosting the rainfall activity chiefly in southern and central Keralam.

However, the intensifying El Niño over the Pacific is also expected to influence rainfall patterns over the Indian subcontinent. Rising atmospheric and sea-surface temperatures is expected to increase the moisture-holding capacity of the atmosphere. According to the Clausius-Clapeyron relation, every 1°C rise in air temperature increases the atmosphere’s moisture-holding capacity by about 7%.

Additional heat

The additional heat can contribute to intense rainfall and stronger cyclonic systems, interspersed with prolonged dry spells, climate scientists said. However, the transfer of energy through the atmosphere-ocean system is not instantaneous, and the effects could sometimes extend into the following monsoon season. Theoretically, therefore, an increase in cyclonic activity could be seen this year or the next.

At the same time, El Niño can suppress the vertical movement of air, disturbing the ascent of warm, moisture-laden air and thereby suppressing rainfall. The end result could be a pattern of short, intense wet spells triggered by Bay of Bengal systems, followed by prolonged dry periods, scientists said.

Keralam has recorded a normal northeast monsoon in 66 of the 125 years from 1901 to 2025. The season was deficient in only 29 years and in excess in 30 years, meaning rainfall was normal or above normal in 96 years. The highest northeast monsoon rainfall was recorded in 2021, when Kerala received 1,026.3 mm against the normal 478.1 mm. The lowest was recorded in 2016, when the State received only 185 mm, and a strong El Niño also marked 2016.