IMD: Heavy rain in Keralam, South Karnataka, TN, Puducherry for 4 days from Thursday

European Centre for Medium-Rane Weather Forecasts suspects a bulk of rain during the opening spell of north-east monsoon being directed into the seas away from Sri Lanka/Tamil Nadu coasts. | Photo Credit: www.tropicaltidbits.com

The north-east monsoon could set in over the South Peninsula within next two days, even as the India Meteorological Department (IMD) appeared on Monday to have dropped its watch for Tuesday for a low-pressure area that the south-east Bay of Bengal was thought to come up with.

The trigger for the emerging wet spell may instead be a trough linking cyclonic circulations over the south-west and central Bay off Sri Lanka coast with the parent circulation over the south Andaman Sea. This circulation has merged into this trough, which could help channel the easterlies and usher in the north-east monsoon.

The 2026 season is set to open with a six-day wet spell from Wednesday/Thursday, with isolated heavy rainfall forecast over several parts of the South Peninsula. Tamil Nadu, Puducherry and Karaikal are likely to bear the brunt of the initial spell, followed by Kerala and Mahe from Thursday, an IMD said on Monday.

The rain belt is expected to extend across coastal Andhra Pradesh, Yanam and South Interior Karnataka for four days from Thursday; Coastal Karnataka, North Interior Karnataka and Rayalaseema for three days from Friday; and Telangana on Saturday. Isolated to scattered, and at times fairly widespread to widespread overlapping rainfall is forecast at many places across these regions during these days, with pockets of heavy rain.

Historical performance of the north-east monsoon shows the meteorological subdivision of Tamil Nadu, Puducherry and Karaikal received its highest seasonal rainfall in 2015 (floods) and 2021. The absolute lowest point was 2016 (-62 per cent). It remains the only subdivision in India where rainfall during north-east (October to December) monsoon rainfall exceeds that during the south-west monsoon (June to September).

For Kerala and Mahe, 2011-2025 has delivered a highly volatile season marked by excesses and severe deficits in 2016 and 2023. The subdivision logged exceptionally high excess in 2021 and 2023 (+27 per cent) that contrasted heavily with dry spells during strong El Niño interludes where its interior catchments have routinely failed.

With the Bay of Bengal primed for the retreating monsoon nearing its final exit, the South Peninsula is entering a consequential wet phase of the seasonal calendar. The coming days will determine how quickly the easterlies take charge, and whether the expected onset of north-east monsoon brings a sustained spell of rain to the region after the south-west monsoon’s long retreat leaves behind a significant deficit.

The emerging weather pattern is already offering a foretaste of the transition, with rain, thunderstorms, lightning and gusty winds unfolding over several parts of southern India. These conditions could intensify on either side of October 15, around which the north-east monsoon is likely to set in over Tamil Nadu and adjoining areas.

The south-west monsoon must complete its retreat from the mainland before the seasonal transition is fully established, although the two processes can overlap in time. This year, its final retreat and the onset of north-east monsoon are expected to converge, making the coming days a crucial window for the South Peninsula.

Fairly widespread to widespread rainfall is expected over Kerala and Mahe for four days from Thursday; Coastal Andhra Pradesh and Yanam, Lakshadweep and South Interior Karnataka for three days from Friday; Coastal Karnataka and North Interior Karnataka over Saturday and Sunday; and Rayalaseema on Thursday and Friday.

Isolated to scattered rainfall may persist over Tamil Nadu, Puducherry and Karaikal for six more days. Kerala and Mahe are likely to receive such rainfall for two days, while Coastal Andhra Pradesh and Yanam, Lakshadweep and South Interior Karnataka could see it for three days. Coastal Karnataka and North Interior Karnataka are forecast to receive isolated to scattered rainfall on Thursday and Friday, with Rayalaseema likely to experience similar conditions over the weekend. Telangana, meanwhile, could see rain for four days from Thursday.