Tamil Nadu is bracing for a wet and vigorous phase of the Northeast monsoon as two weather systems in the region are expected to strengthen and trigger heavy rainfall, particularly across the southern districts. Northern parts of the State, including Chennai, may also come under intense rain spells on November 29 and 30.

The Regional Meteorological Centre (RMC), Chennai, is closely tracking the evolving systems to assess how they may alter the rainfall pattern in the coming days.

Currently, a well-marked low-pressure area persists over Malaysia and the adjoining Strait of Malacca, accompanied by an associated cyclonic circulation. Meteorologists expect it to intensify into a depression over the South Andaman Sea by Tuesday and further strengthen into a cyclonic storm in the South Bay of Bengal by Thursday.

If upgraded to a cyclonic storm, it will be named ‘Senyaar’, as proposed by the United Arab Emirates.

Meanwhile, another weather player-a prevailing upper-air cyclonic circulation over the Comorin region—is likely to develop into a low-pressure area by Tuesday and intensify subsequently.

This system has already been influencing widespread rainfall across Tamil Nadu. The State, which was facing a seasonal rain deficit until recently, has now swung into surplus territory by 5% as of Monday, following incessant downpours over the last two days. Since October 1, Tamil Nadu has recorded 34 cm of rain, surpassing the seasonal norm of 32.3 cm. However, a few districts, including Chennai, Chengalpattu, and Dindigul, continue to trail behind.

Rainfall activity remained vigorous during the 24 hours ending 8.30 a.m. on Monday, with several locations witnessing heavy to very heavy rain.

Oothu in Tirunelveli district recorded the highest at 23 cm. While the wet spell is expected to extend till the end of November, the RMC has forecast heavy rain over Tirunelveli, Ramanathapuram, and two other districts on Tuesday.

As both weather systems gain strength, intense rainfall is likely to expand across the southern and delta districts. The department has issued orange and yellow alerts for multiple districts from November 28 to 30.

From midweek, northern districts, including Chennai and Chengalpattu, are expected to see very heavy rain on November 29. An orange alert has been issued for Tiruvallur district for November 30.

According to B. Amudha, Head (Additional in-charge), RMC Chennai, the interaction of three weather systems—including another cyclonic circulation over the southeast Arabian Sea—is contributing to dynamic changes in rainfall behaviour.

She noted that such interactions, especially in the equatorial trough, are typical during the Northeast monsoon, with systems feeding moisture to one another.

“We are monitoring the possibility of the system near the Strait of Malacca merging with the one over the Comorin area and moving as a combined disturbance. We will have more clarity in the next two to three days,” she said.

Commenting on the intense downpours in the southern districts, Ms. Amudha explained that localised weather patterns along the ghats can amplify rainfall.

She added that November is likely to record normal rainfall, with system-driven rains expected to offset earlier deficits.